So, what exactly is the difference between an Inductor and Inductance? Inductance is the characteristic of a conductor to oppose changes in current by producing an electromotive force.  An Inductor is an electronic device whose main purpose is to oppose changes in current in a circuit by utilising inductance. The inductance of an inductor can be altered by changing its physical properties which include the core material used for the inductor, increasing the cross sectional area of the magnetic core, and increasing the number of turns of the coil. 

What is inductance?

Conductors have many different properties which include electric resistivity, magnetic permeability, conductivity, malleability, ductility, thermal conductivity, etc. Another important property of a conductor is its Inductance, which defines the ability of the conductor to oppose changes in current in the form of an electromotive force or voltage. The units of the inductance are given in Henrys (named after Joseph Henry who first discovered inductance) denoted by H. However, you might also associate inductance with the letter L. One Henry causes a Voltage of one volt, when current is changing at a rate of one ampere per second.  The inductance of an inductor is largely influenced by the cross-sectional area of the conductor, as well as the magnetic permeability of nearby materials. 

Below is the formula for inductance for a coil of wire;

What is an inductor?

An Inductor is an electronic component whose main purpose is to provide inductance in electrical and electronic circuits. Inductors are constructed using an inner core material (with high magnetic permeability), and a coil of wire wrapped around this core (as seen in the image below).

An inductor is designed to have a certain amount of inductance which is controlled by manipulating the different variables in the equation for inductance;

• Number of turns of wire of the coil (the more turns, the higher the inductance).
• Coil area 
• Coil length
• Core material permeability (the greater the magnetic permeability of the core material, the greater the inductance). 
• Core material cross-sectional area

The ability of an inductor to provide inductance in circuits has many different applications which include;

• Tuning circuits,
• Choking, 
• Blocking,
• Attenuating and
• Filtering/Smoothing high frequency

Difference between an inductor and inductance

The electrical and electronic world is filled with a plethora of components, devices, terms, units, etc. So things can get confusing fast. One major confusion is the difference between an Inductor and Inductance. As we have just taken a look at inductance and inductors individually, we can look at the differences between them. Inductance defines the property that all conductors have, which is to oppose changes in current. Inductors are components designed to have higher levels of  inductance (compared to a straight piece of wire) and provide inductance in circuits. So, inductance is a property, and inductors are components with a set value of inductance. The amount of inductance that an inductor has can be controlled by varying the number of turns of coil, coil area, coil length, core material cross-sectional area, and core material magnetic permeability.

The post Difference between an inductor and inductance appeared first on Electronic Guidebook.

So, what is the main difference between a resistor, capacitor and inductor?

The main difference between a resistor, capacitor and inductor is what each does with energy. A resistor dissipates energy in the form of heat, a capacitor stores energy in the form of an electric field, and an inductor stores energy in the form of a magnetic field. Also, each of these components have different functions which play an essential role in electrical and electronic circuits. This article shall take a more in-depth look at each of these.

The resistor, capacitor and inductor

Before we take a look at the differences between these three components, let’s take a brief look at each component to see what they are all about.

What is a resistor?

Of the three components, the resistor is the most commonly used. The resistor plays a vital role in electrical and electronic circuits. Its main purpose is to limit the flow of current. It does this by providing a resistance to the flow of current. The greater the resistance, the less current can flow, and the lower the resistance, the more current can flow. Current is a form of electrical energy and when it flows through a resistor, this energy is converted into heat energy (which is dissipated into the surroundings). 

Other than just limiting current, a resistor can be used for many other purposes which include, voltage division, heat generation, matching and loading circuits, gain control and setting time constants. 

What is a capacitor?

Next up we have the capacitor. A capacitor is composed of two conducting plates that are separated by a dielectric (which is an insulating material). The main purpose of a capacitor is to store energy in the form of electrical energy. This stored energy can be released back into the circuit when required. The amount of electrical energy a capacitor is capable of storing is determined by its capacitance. The higher the capacitance, the more energy it can store, and vice versa. Capacitors allow Alternating Current (AC) to pass, but block Direct Current (DC).

Other than energy storage, capacitors are used for power conditioning, noise filtering, remote sensing, and signal coupling/decoupling. 

What is an inductor?

Last, but not least, is the Inductor. Inductors, also sometimes referred to as a coil or choke, are an electronic component that stores energy in a magnetic field when current flows through it. They are constructed using an insulated copper wire that is wound into a coil around a core (which is usually magnetic iron or ferrite). Inductors also have the ability to oppose changes in current which is determined by their Inductance. The higher the inductance the more effective an inductor is at opposing changes in current. Because of this fact, inductors block AC, but allow DC to pass. A wire with more coils (turns) is going to have a higher inductance. 

The applications of inductors include; choking, blocking, attenuating, filtering/smoothing high frequency noise, storing and transferring of energy. 

What is the difference between a resistor, capacitor and inductor?

The main difference between a resistor, capacitor and inductor, is what happens with current flowing through them. Energy is the common theme they share, however, what happens with energy in each of them varies. When current flows through a resistor, energy is dissipated in the form of heat. In a capacitor energy is stored in the form of an electric field when current flows through it. And when current flows through an inductor, energy is stored in a magnetic field. 

Other than that, the other major differences between these components include;

• Main functionality
• Construction

Main functionality

Other than what each does with energy, the other difference between a resistor, capacitor and inductor, is the main functionality and the applications they are used in. The main function of a resistor is to limit current, whereas the main function of a capacitor is to store charge for later use and the inductor’s primary purpose is to oppose any change in current. As there is a difference in their functionality, so too are the applications they will be used for.

Construction

How a resistor, capacitor and inductor is constructed is another difference. As we just saw, each has a different function. They get these unique functions due to the way that they are constructed (as well as the materials that they are constructed with). 

Difference between a capacitor and inductor

Of the three components, the capacitor and inductor are quite similar in that they both store energy. But, the way they store energy is their major differentiation. A capacitor stores energy in an electric field, while an inductor stores energy in a magnetic field. But, there is another difference between these two components. 

There are two types of current that can flow through an electrical/electronic circuit. The current can either be an Alternating Current (AC) or a Direct Current (DC). When it comes to a capacitor, it blocks Direct Current, but allows Alternating Current to pass. Inductors on the other hand allow Direct Current to pass, but block Alternating current.

Summary of the differences between a resistor, capacitor and inductor

Below is a table summarising the differences between a resistor, capacitor and inductor. 

The post What is the difference between a resistor, capacitor, and inductor? appeared first on Electronic Guidebook.

Resistors, Rheostats, and Potentiometers

Before we can take a look at the differences between these components, it will help to first learn a bit about them individually. So let’s take a quick look. 

What is a resistor?

A resistor is a crucial component used in almost every (if not all) electrical/electronic circuits. It is a two terminal passive component which has the main purpose of limiting the current flow. It does so by providing a known resistance. Higher resistances allow less current to flow, while lower resistances allow more current to flow. The resistor’s resistance comes down to the materials used as well as how it is constructed.  However, these materials need to be able to  allow current pass while still providing a resistance. 

While the resistor has the main function of limiting current, it has many other uses which include voltage division, heat generation, matching and loading circuits, gain control, as well as setting time constants. 

What is a rheostat?

Rheostats are components which have the ability to vary their resistance. By varying the resistance, rheostats can control the flow of current. Because of this unique ability rheostats are used in applications that include altering generator characteristics, light dimming, and motor speed control. 

Resistance of resistors, and rheostats come down to certain factors which are their length, cross-sectional area and material. The cross-sectional area, and material of a rheostat remain constant. So, to be able to vary its resistance, rheostats vary their physical length. 

A rheostat has the capability of varying its resistance because it has the ability to vary its length. While its cross-sectional area and what it’s made of remain constant, its length can be altered.

All rheostats come with three terminals. Two of the three terminals are fixed (in the above diagram its terminal 1 and 3). The middle terminal (terminal 2), is not fixed and can be moved backward and forward. By moving this terminal back and forth, we are changing its position on the resistive track (which is often a coil of wire as seen above) thus altering the rheostat’s length (and resistance in the process). 

While it has three terminals, only two terminals get connected to the circuit. This includes one of the fixed terminals, and the terminal that moves. 

What is a potentiometer?  

Finally, we have the Potentiometer. The potentiometer is very similar to the rheostat. It too has three terminals and the ability to vary resistance. However, the potentiometer has an additional capability which is to vary the voltage and act as a voltage divider.

The most commonly used potentiometer is the Rotary Potentiometer. This type of potentiometer has a knob which the user can rotate backwards and forwards to alter its characteristics. This knob is connected to a semi-circular resistive track via a contact. As the contact moves along the resistive track, the voltage is obtained between one fixed terminal and the middle sliding terminal.

Potentiometers also have three terminals as seen above. All three terminals are utilised to be able to use the potentiometer as a voltage divider. However, if you just want to vary resistance, only two of the end terminals are connected. 

What is the difference between a resistor and rheostat?

The main difference between a resistor and rheostat is that the resistance of a resistor is fixed, whereas the resistance of rheostat isn’t. The resistance of the rheostat can be varied by moving its middle terminal which changes the physical length of the rheostat, and thus changes its overall resistance. Resistors come with fixed values of resistance due to the fact that their length, cross-sectional area and materials used are all fixed and cannot be altered. 

What is the difference between a resistor and potentiometer?

The main difference between a resistor and potentiometer is that a resistor has a fixed resistance, while a potentiometer can vary its resistance. Just like the rheostat, the potentiometer has the ability to alter its physical length which results in its ability to alter its overall resistance as well. 

What is the difference between a rheostat and potentiometer?

The main difference between a rheostat and potentiometer is that the potentiometer can vary voltage and resistance, but a rheostat can only vary its resistance. A potentiometer has the ability to vary voltage because all three of its terminals are connected in a circuit. An input voltage is applied to the end terminals (the entire length of the potentiometer). This results in an output voltage between one of the fixed end terminals and the moving middle terminal. A rheostat is different because only two of its terminals are connected to a circuit so the input voltage cannot be divided. 

Also, a potentiometer can be used as a rheostat (and just vary resistance), but a rheostat cannot be used as a potentiometer and vary voltage. 

The post Difference between a resistor, rheostat and potentiometer?
appeared first on Electronic Guidebook.

Within the electrical and electrical world exists a myriad of different components each with their own unique capabilities.

One of these components is the Diode. 

But, there isn’t just one type of diode out there. It has a number of different variations, and the two commonly used in circuits and devices are the PN Junction and Zener Diodes.

So, what is the difference between a PN Junction and Zener diode? The main difference between a PN Junction diode and a zener diode, is that the PN junction only allows current to flow in one direction, whereas the zener diode allows current to flow in both directions.

Other notable differences include;

• Schematic Symbol
• Materials used
• Doping level and 
• Application

This article shall take a close look at these two types of diode, as well as a more in-depth look at the key differences. 

What are diodes?

Before we dive into looking at the differences between a PN Junction and Zener diode, it will first help to learn about the diode (however if you are well versed with diodes, you can skip this section). 

Resistors help limit current, capacitors store charge, switches turn circuits on and off, etc.

So what is a diode and what is its purpose?

A diode is a device which is constructed using semiconducting material and only allows current to flow in one direction. 

It acts like an open switch (no current flow) in one direction, and a closed switch (allows current to flow) in the other direction. 

Diodes are passive devices and have a polarity ( have a positive and negative terminal and need to be wired the right way in a circuit).

The positive terminal of the diode is known as the anode, and the negative terminal is known as the cathode. 

Below is an image of a conventional diode along with its schematic symbol highlighting the terminals. 

Different types of diodes

The diode has a number of different variations, each having unique characteristics that will set them apart from their peers.

These unique characteristics will also make each type of diode suitable for a certain type of application.

The different types of diode include;

• PN Junction Diode
• Zener Diode
• Tunnel Diode
• Schottky Diode
• Varactor Diode
• Diac
• Triac
• SCR
• Light Emitting Diode (LED)
• Photodiode

This article shall take a closer look at the PN Junction and Zener diode and the key differences between them.

What is a PN junction diode

Let’s start our journey with the PN Junction Diode.

So what exactly is this diode all about? 

They are aptly named PN Junction diodes because they are composed of a p-type and n-type semiconducting material which are fused together and form a junction.

The P-region and N-region are separated by a depletion region. 

These diodes are also often referred to as rectifier diodes because they are commonly utilized in applications where rectification is necessary (have the ability to convert an alternating current (AC) into a direct current (DC)). 

It is a two terminal device with positive (anode), and negative (cathode) terminals and has the same schematic symbol we saw earlier. 

How a PN junction diode works

PN junction diodes are the simplest of the semiconducting devices and have the ability to only allow current to pass through them in one direction.

This can only happen when they are forward biased.

So what exactly does it mean to be forward biased?

When we talk about diodes, there are three possible modes of operation, or biases;

• Zero Bias
• Forward Bias
• Reverse Bias

Zero bias occurs when there is no voltage applied across the diode.

Forward bias is when a voltage is applied to the diode. However this is when the positive and negative terminals match up with the positive and negative terminals of the voltage source respectively (positive to positive, and negative to negative).

Reverse bias is when a voltage is applied to the diode but in the reverse direction (positive to negative, and negative to positive). 

IV characteristics of diodes

Diodes do not have a linear relationship with voltage, but rather have an exponential  Current (I) – Voltage (V) relationship.

This IV relationship is known as the IV Characteristic and is given in the form of a graph as seen below.

The IV characteristic shows us how the diode performs under zero, forward and reverse bias conditions. 

How a PN junction operates in the forward bias

When discussing the operation of a PN junction diode, we are only concerned about the zero and forward bias conditions (as they can only allow current to flow in the forward direction).

So how does a PN Junction diode work?

To allow current to flow in the forward direction, the diode needs to first be forward biased.

But first, a sufficient amount of voltage needs to be applied in order for current to flow freely. The voltage level required is known as the knee or forward voltage.

For PN junction diodes this is usually 0.3V (Germanium), and 0.7V (Silicon).

When the supply voltage equals (or exceeds) the forward voltage, current starts to flow through the PN junction diode. 

A little increase in voltage after the forward voltage sees a large increase in current.

When a reverse voltage is applied to the PN junction diode making it reverse biased, its depletion layer increases thereby increasing its overall resistance and blocking current flow. 

What is a zener diode  

Next up we have the Zener Diode.

So what awesome powers does this type of diode hold?

Let’s take a look.

The zener diode is also constructed using semiconducting material like the PN Junction diode. However it has the ability to conduct current in the forward and reverse direction.

It has the ability to conduct in the reverse direction thanks to a special heavily doped p-n junction. 

Zener diodes are also two terminal devices with an anode (+) and cathode (-), however their schematic symbol is different. 

The zener diode was discovered by Clarence Zener who discovered its electrical properties and is how it got its name.  

How a zener diode operates

While the PN junction is only limited to allowing current to flow in the forward direction, the zener diode is capable of conducting current in both the forward and reverse direction.

When operating in the forward bias, the zener diode has the same operation as the PN junction diode. 

So it requires a sufficient voltage which equals the forward or knee voltage before it can allow current to start flowing in the forward direction. 

However, if a reverse voltage is now applied to the zener diode thus causing it to be reverse biased its operation changes. 

If we look at the IV characteristic graph from before (in the third quadrant), we can see what happens to current when a reverse voltage is applied.

Initially there is a small leakage current that flows through the zener diode. 

We know that in the forward bias there is a critical voltage known as the knee or forward voltage, which is the amount of voltage needed before current can flow.

In the reverse bias, this voltage is known as the breakdown voltage (Vz). 

When the reverse voltage equals, or is greater than the breakdown voltage, a large reverse current flows through the zener diode. 

Key differences between a PN junction diode and a zener diode

Now that we have had a close look at the PN Junction and Zener diode, we can delve into their key differences.

Difference #1 between a PN junction and zener diode: Direction of current flow

The first most obvious and main difference between these two diodes is direction of current flow.

A PN junction diode only has the ability to conduct current in the forward direction (when the voltage applied across its terminals is greater than the forward voltage of the diode).

Zener diodes on the other hand have the capability to conduct current in the forward and reverse direction. 

In the forward bias zener diodes operate the same as PN junction diodes. However, when reverse biased, a small leakage current flows until its breakdown voltage is matched or exceeded, which then sees a steep rise in current. 

PN junction diodes are always used in the forward bias, whereas zener diodes are commonly used in the reverse bias. 

Difference #2 between a PN junction and zener diode: Schematic symbol

There are many different types of components that exist in the electrical and electronic world. Each of them has its own unique purpose.

But, when designing circuits, or analyzing circuit diagrams we need a way of distinguishing between the different types of components (otherwise things would get confusing real fast).

This is where schematic symbols play a crucial role. 

They help us identify particular electrical/electronic components as each of them will have their own unique schematic symbol. 

Since the PN junction and Zener diode are two variations of the diode, and have separate functionalities, each gets its own schematic symbol.

This will help us distinguish between a PN junction and zener diode in circuit diagrams. 

Difference #3 between a PN junction and zener diode: Doping level

Diodes are semiconducting devices that are constructed using, well, semiconductors. 

But what exactly are semiconductors and doping?

Semiconductors are materials which have properties of both a conductor as well as an insulator. 

Doping of semiconductors is a process used to add or remove the number of electrons and holes in semiconductors.

This process alters the electrical, optical and structural properties of semiconductors. Increasing the doping level of a semiconductor makes it act more like a conductor. 

This is the next difference between a PN junction and Zener diode is their doping levels. 

A PN junction diode has lower doping levels compared to zener diodes which are heavily doped. 

Difference #4 between a PN junction and zener diode: Materials used

The next difference is the materials that each type of diode is composed of. 

Common materials used to construct diodes include Silicon, Germanium and Gallium Arsenide. 

However, PN junction diodes will only be constructed using a single material, while zener diodes will use a mix of these materials. 

Difference #5 between a PN junction and zener diode: Applications

As you have just seen, while they are both diodes, there are some key differences between the PN junction and zener diode. 

Each has their own unique abilities and is why they share separate applications (which is our next and final key difference).

The PN junction diode is mostly used in the applications seen below;

• Rectification
• Voltage-Controlled oscillator
• Mixing signals
• Lighting systems
• Detection of signals 
• Solar cells

Whereas zener diode can be seen in applications which include;

• Voltage Regulation
• Reference elements
• Surge Suppressors
• Clipping circuits

PN junction vs Zener; which is better?

So, you need a diode for your circuit. 

What do you choose, the PN Junction or Zener diode?

Which is the better option?

There is no right answer to this as one diode is not better than the other. Picking the right diode comes down to the needs of your application.

Each diode is used for different applications according to how its characteristics best help.

For example, you will not be able to use a PN junction diode for a voltage regulation application, as it will not be able to perform the job.

A zener diode is the best option here.

So, it really depends on the needs of your application when selecting the right diode.

The post Difference between a PN junction diode and a zener diode appeared first on Electronic Guidebook.

They are a semiconducting device used for either amplifying or switching electrical signals. 

Transistors come in a variety of forms. While their end goal remains the same (switching of signals), the way they go about doing so may differ. 

Materials used, as well as their construction are other factors that differ. 

The two most common types of transistor used are the BJT and JFET.

So what is the difference between a BJT and JFET? The major difference between a BJT and JFET is that a BJT is a current controlled device, and a JFET is a voltage controlled device. 

However, there are many other factors and differences between a BJT and JFET which this article shall take a closer look at. 

A brief look at the transistor

As we just saw above, transistors are a type of semiconducting device, which in essence have the function of the humble switch.

They can be used to either conduct  or insulate current or voltage. Another neat function of a transistor is the amplification of current or voltage. 

Construction of a transistor commonly consists of placing an oppositely doped semiconductor between two similarly doped semiconductors.

Transistors are usually three terminal devices and have three regions of operation;

• Cut-Off
• Saturation
• Linear/Ohmic

Cut-off region

When the MOSFET is in the cut-off region the device is considered to be in its ‘OFF’ state. When it is OFF, no current flows through it. 

Just like when a mechanical switch is open and stops the flow of current as well.

Saturation region

Saturation is when the current flow through the MOSFET is a constant value. In this region it behaves like a closed switch allowing current to flow freely. 

Linear/Ohmic region

Last but not least is the Linear/Ohmic region. 

In this region of operation, an increase of voltage across the drain and source sees an increase in current through the MOSFET as well.

A voltage or current is applied to one of the pins to activate (turn on) the transistor to allow current to flow. 

Closer look at the BJT and JFET

Before we dive into the differences between these two transistors, it will help to first learn a little bit more about each of them individually. 

So let’s take a look.

What is a BJT

Let’s start with the BJT.

A BJT, or Bipolar Junction Transistor is a bipolar device which has three terminals; Base (B), Emitter (E), and Collector (C).

A small current at the Base, turns it on allowing for a larger current to flow between the Collector and Emitter.

Construction and working principle of a BJT

A BJT can be further divided into two types; PNP and NPN.

PNP BJT

This type of BJT has an n-type material placed between two p-type materials. The flow of current is controlled by the device.

NPN BJT

This configuration of the BJT has p-type material in between two n-type materials. NPN transistors are commonly used to amplify weak signals. 

What is a JFET

Now let’s take a look at the JFET which stands for Junction Field Effect Transistor. 

The JFET is a type of FET (Field Effect Transistor) which is a three terminal unipolar device and also has three terminals; Gate (G), Source (S), and Drain (D).

A voltage at the gate turns ‘ON’ the JFET allowing for current to flow between the source and drain. 

Construction and working principle of a JFET

In the JFET, there is no PN junction. It uses a narrow piece semiconducting material which has a high resistance.

This forms a ‘Channel’ which can either be N-type or P-type silicon.

The JFET can be split into two types; N-Channel and P-Channel.

N-Channel JFET

In this type of JFET, the channel is doped with donor impurities resulting in a negative flow of current. The conductivity in N-channel JFETs is higher due to a lower resistance.

P-Channel JFET

P-Channel JFETs have their channel doped with acceptor impurities resulting in a positive flow of current which is in the form of holes. 

What is the difference between a BJT and a JFET?

Now that we have briefly covered both the BJT and JFET, let’s first take a look at the major differences between these two types of transistor. 

Then later we shall look at other notable differences. 

Difference #1 between a BJT and JFET: Current vs Voltage controlled

Earlier you would have seen that the BJT is a current controlled device, whereas the JFET is voltage controlled. 

This is the first major difference between a BJT and JFET.

But what does it mean if a transistor is current or voltage controlled?

A transistor that is voltage controlled, has voltage as the controlling parameter. What this means is that the flow of current at the output terminals is controlled by a voltage at the input terminal. 

The output current is a function of an input voltage. 

On the other hand, a transistor that is current controlled, has current as the controlling parameter. This means that the flow of current at the output terminals is controlled by a current at the input terminal.

Output current is a function of an input current. 

Difference #2 between a BJT and JFET: Unipolar vs Bipolar

Transistors that are bipolar use electrons, as well as holes as charge carriers. Whereas, transistors that are unipolar use only one kind of charge carrier; either electrons or holes.

The next difference is that a BJT is a bipolar device (hence the name Bipolar Junction Transistor), while a JFET is a Unipolar device.

A N-channel JFET has electrons as the major carrier, while a P-channel JFET has holes as the major carrier. 

Difference #3 between a BJT and JFET: Input Impedance

Input impedance is an important characteristic of transistors which defines the ratio of input voltage to input current.

Input impedance helps determine the measure of the loading effect on the transistor. 

A low impedance results in the transistor having a low-frequency response and a large input power requirement. 

JFETs have high input impedances, while BJTs have low input impedances.

Difference #4 between a BJT and JFET: Noise level

Noise is an unwanted signal in electronic components, devices and circuits. It has a negative effect on the performance bringing down the overall efficiency.

In an ideal world there would be no noise, however, we do not live in an ideal world so noise will always be present.

When it comes to noise level for transistors, JFETs are less susceptible to noise compared to BJTs.

Difference #5 between a BJT and JFET: Voltage gain

The main function of a transistor is to act as a switch. 

But, they have other functionalities as well. Transistors are often referred to as amplifying devices as a relatively small input can cause a large change in the output. 

The voltage gain of a transistor is defined by the ratio of the output voltage to the input voltage. 

A JFET has a higher voltage gain than a BJT.

Difference #6 between a BJT and JFET: Current gain

Current gain is similar to voltage gain with the only difference being that the ratio is now output current and input current.

The JFET again has a higher current gain than the BJT.

Difference #7 between a BJT and JFET: Switching times

If you were to close and open a mechanical switch, there is going to be a delay. You will not be able to switch between the two states instantaneously.

This is true for the switching of transistors electrically as well.

There is going to be a delay between current flow and when current or voltage is applied to the appropriate terminals of the transistors (Base for the BJT, and Gate for the JFET).

Also there will be a delay to when current stops flowing when voltage or current is removed from these terminals. 

These delays between ‘ON’ and ‘OFF’ are known as the switching times.

JFETs have high switching times, while BJTs have medium switching times. 

Summary of the differences between a BJT and JFET

The differences that we just covered of the JFET and BJT are the most notable ones. However, there are many other differences that need to be considered as well. 

Below is a table that summarises other differences between a JFET and BJT.

Which is better a BJT or JFET?

As you just saw, there are many characteristics that contribute to the overall workings of a transistor. And there are many differences between the BJT and JFET when you compare these characteristics. 

So, which is better to use, a BJT or JFET?

Well there is no right answer to this question as one type of transistor has its own unique purpose and one   might be better suited for an application compared to the other.

It really comes down to the needs of the application and which transistor can meet those needs.

The post Difference between a BJT and a JFET appeared first on Electronic Guidebook.

Components such as capacitors, inductors, diodes, thermistors, transformers, etc. 

However, one very crucial component that is missing from that list is the Resistor. I would be surprised if you weren’t able to find one in a circuit. 

The resistor can be further divided into two categories; Fixed Resistor and Variable resistor. 

But, what is the difference between a fixed resistor and variable resistor? The main difference between a fixed resistor and variable resistor is that a fixed resistor has a fixed resistance, whereas the variable resistor has variable resistance (it has a range of resistances which you can set using a knob or slider). 

There is more to just resistance when it comes to the differences between a fixed and variable resistor. Things like construction, application, etc. 

This article shall take a closer, more in-depth look. 

Deeper look at a fixed and variable resistor

Let’s take a closer look at the fixed and variable resistor. This will help you better understand the differences between the two later on. 

What is a resistor?  

Let’s take a closer look at the Resistor. 

As mentioned at the start, there are many different types of components and devices in the electrical and electronic world, each with their own unique abilities which help perform a certain function within a circuit. 

The Resistor is a fundamental electronic component that can be found in almost all circuits.

So what is the definition of a resistor? 

A resistor is a passive electrical and electronic component, whose main purpose is to ‘resist’ the flow of current in a circuit. Also, rather than having an ambiguous resistance value, resistors are created with a set resistance value. 

The bigger the resistance, the less current can flow, and the lower the resistance, the more current can flow.

It is known as a passive component due to the fact that it has no means of generating its own power, but rather dissipates power in the form of heat. 

The fixed resistor

As the name might suggest, fixed resistors have a resistance that is fixed regardless if there is a change in voltage.

It cannot physically change its resistance. 

For example, if you bought a 10 ohm fixed value resistor, this is the only resistance that the resistor is going to be able to provide.

In an ideal world, the resistor would provide a fixed resistance at all times. However this is not the case, as their resistance varies slightly with temperature (which we shall look at later). 

Fixed resistors are the most commonly used in circuits. Their value is chosen during the circuit design phase using calculations using Ohm’s Law. 

Different types of fixed resistor

Below are the different types of fixed resistor available;

• Wire Wound 
• Carbon composition 
• Carbon film
• Metal Film
• Metal-oxide film 
• Metal glaze
• Foil

Wire wound  fixed resistor

This type of resistor has an insulating ceramic rod that is wrapped in wire (with the wire being copper due to its high conductivity). 

It is the most widely used type of fixed resistor. 

Carbon composition fixed resistor

Have a cylindrical form with metal caps at either end of the cylinder. Inside the cylinder is a substance that is a mixture of carbon power and ceramic. 

While used primarily in the early 1960’s, this type of fixed value resistor isn’t used a lot anymore due to its high cost and low stability. 

Carbon film fixed resistor

Has a very similar construction to the carbon composition resistor. However, a carbon film is placed atop a ceramic substrate. 

This type of fixed value resistor produces less noise when compared to carbon composition resistors. 

Metal film fixed value resistor

The metal film resistor has the same construction as the carbon film. But, rather than using carbon as the material of the film, other metals are used.

Metals used in metal film resistors are usually Nickel Chromium, Tin or Antimony.

The resistance of metal film is less affected by temperature. 

Metal oxide fixed value resistor

Has the same construction as carbon film, and metal film resistors. Again, what sets them apart is the material used. 

The film in this resistor is a metal oxide such as Tin Oxide.

They cost less compared to carbon composition resistors, and can be used at higher temperatures. 

Metal glaze fixed value resistor

Use a composition of glass powder and metal particles to restrict the flow of current.

Its resistance is also less affected by temperature. 

Foil fixed value resistor

Last but not least are foil resistors. 

They are made using an alloy (a material composed of two or more metallic elements). The foil is created from an alloy of nickel and chromium. 

Of all the different types of construction for fixed value resistors, these are the most accurate and stable. 

They also produce far less noise.

What is a variable resistor?

Next, we have the Variable Resistor.

This type of resistor has the ability to vary its resistance between two set values (with the lower usually being 0 ohms).

Note, this does not mean it’s restricted to those values, it can have a range of values which sit within the range of its lower and upper resistance limits. Its incremental value depends on the resolution of the variable resistor. 

For example if you have a 10k variable resistor, you would be able to set its resistance at any value between 0 and 10k ohm. 

So, you could set it at 10, 100, 1k, 2.5k, 5.7k, 8k etc. 

Below are the most commonly used circuit symbols for variable resistors;

Construction of a variable resistor

The construction of a variable resistor is basically a fixed resistive element along with a wiper that sits on the resistive element. 

The slider can be adjusted (by means of a slider or knob which you control) to sit anywhere along the resistive element thereby adjusting the overall output resistance. 

As you can see there are three terminals and the resistive element is connected to terminals 1 and 3. To use it as a variable resistor, you have to make connections to terminal 1 and 3.

Other abilities of a variable resistor

The variable resistor is quite the versatile component. 

The great thing about it is that it has an added ability, which is to vary voltage. When used to vary voltage, it is known as a Potentiometer.

To use it as a potentiometer, you would connect terminals 1 and 3 to GND and VCC (it doesn’t matter which terminal gets connected to what). 

The varied voltage is then presented at terminal 2. 

The main difference between a fixed resistor and variable resistor

So, we have learnt what a fixed and variable resistor are individually. But, what is the main difference between the two?

While the overall function of both remains the same, which is to provide resistance, the main difference between a fixed and variable resistor is their Resistance values. 

Fixed resistors are created to have a specific known resistance value that is set and cannot be changed (hence why they are called fixed resistors).

Variable resistors on the other hand offer a range of resistances (between their minimum and maximum values) which you can alter by means of a slider or knob.

Also, they are used for specific applications in circuits (which we shall cover later in the article).

The main purpose of a fixed resistor and variable resistor

But, why do we need resistors in the first place? 

Every electrical and electronic component has something known as a Power Rating.

This is a value that indicates how much electrical power is needed by the component to work effectively. Also, the power rating value indicates the maximum allowable electrical power the device or component can handle.

Exceeding this value will cause damage to the component. The power rating can be broken further into; Voltage ratings, and Current ratings. 

This is because power is a product of voltage and current ( P = V x I).

Components will have values for maximum voltage and maximum current ratings that should not be exceeded.

Resistors are important as they allow us to protect components in circuits by limiting the current so that the current ratings of that component are not exceeded (and therefore power rating as well).

Sometimes you might not be able to change the power supply (which means the voltage is fixed), so you will need a resistor to limit the other variable in the power equation (in this instance the current).

However, while resisting current is their main task, they are used in electrical and electronic circuits for other reasons to achieve certain outcomes. 

Let’s take a look at different uses of fixed and variable resistors. 

Applications of a fixed resistor

If you were to pry open any electronic device and look at its circuits, I would be surprised if you didn’t find at least one resistor. 

Fixed resistors have many uses for different applications. Some of the uses include; 

• Reducing current flow 
• Adjusting signal levels
• Dividing voltages 
• Biasing active elements
• Terminating transmission lines 
• Pull-up / Pull-down 

Some of the many applications;

• High frequency instruments
• Power control circuitry 
• DC power supplies 
• Filter circuit networks
• Amplifiers
• Oscillators
• Telecommunications
• Electronic measuring instruments
• Wave generators
• Transmitter
• Modulators / Demodulators
• Instrumentation 
• Voltage regulators 
• Feedback amplifiers  

Applications of a variable resistor

While not as common as its conventional counterpart, variable resistors have more specific applications compared to fixed resistors.

Common uses of a variable resistor include;

• Varying resistance (when used as variable resistor)
• Varying voltage (when used as a potentiometer) 

Common applications of a variable resistor are;

• Televisions
• Audio control (Radios, Stereo systems, Cars, etc)
• Oscillators
• Motion Control
• Transducers 
• Home electrical appliances 
• Motor control (electric vehicles, scooters, golf carts, etc)

Different types of variable resistor and their applications

The variable resistor we just looked at is just one of the most common types which varies its resistance mechanically (twisting a knob, or moving a slider).

However, there are other forms of variable resistors each having its own unique way of varying resistance. 

Let’s take a quick look at each of them. 

Light dependent resistors

The  first on the list are Light Dependent Resistors (LDRs).

However, they have many other aliases that you might know it by, which include, Photoresistor, Photocell, or Photoconductor. 

The resistance of light dependent resistors changes depending on varying light levels. The amount of resistance that changes depends on the intensity of light, as well as the sensitivity of the LDR.

The less light that the LDR is subject to, the higher its resistance (in the order of megaohms) and the more light that shines upon the LDR, the lower its resistance (few hundred ohms).

They are created using a semiconducting material that gives them their light sensing abilities. 

Common applications of the light dependent resistors;

• Smoke alarms
• Photographic light meters
• Streetlights 
• Burglar alarms

Force sensitive resistor

Next up we have the Force Sensitive Resistor (FSR).

The resistance of the force sensitive resistor changes when it is subject to force, pressure or weight. 

How much the resistance changes is proportional to the amount of force being applied. 

When there is no force applied to them, it has an almost infinite resistance (which can be viewed as an open circuit).

When a light force is applied, the resistance ranges around 100kohm.

At maximum force, the resistance can be as low as 200 ohm. 

Note, these values will vary from one FSR to the next. 

FSRs can withstand forces up to 20lb (roughly 100 Newtons). 

Common applications of force sensitive resistors;

• Midi controllers (for music producing)
• Electronic drum kits
• Electronic throttle and brake (automotive)
• Gaming joysticks 
• Sports (target force and accuracy detection)

Thermistor

The Thermistor is a portmanteau of the words ‘thermal’ and ‘resistor’.

These words are chosen because of the fact that the thermistor is a device whose resistance varies depending on ambient temperature. 

There are two types of thermistor; Negative temperature coefficient (NTC) and Positive temperature coefficient (PTC).

The relationship between resistance and temperature in NTC thermistors is inversely proportional. This means as temperature rises, resistance decreases, and vice versa.

In PTC thermistors, the relationship between resistance and temperature is proportional. So, when temperature rises, so does the resistance, and vice versa.

Common applications of thermistors; 

• Fire alarms
• Refrigerators 
• Ovens
• Digital thermometer
• Automotive applications 

Humistor

Last but not least is the humble Humistor (no humsitor is not a combination of ‘humble’ and ‘resistor’).

Rather, the humistor is a combination of the words ‘humidity’ and ‘resistor’.

The resistance of this electronic device varies depending on humidity levels. 

Humidity is the amount of water vapour present in the air. The resistance of the humistor depends on the total amount of water vapour molecules it absorbs.

As humidity increases, the amount of water molecules absorbed by the humistor increases thus causing it to be more conductive which results in its resistance decreasing. 

On the other hand, the less water molecules absorbed, causes the humistor to be less conductive thereby increasing its resistance. 

Common applications of the Humistor;

• Agriculture
• Textile factories (where humidity can affect materials)
• Refrigerators
• Atmospheric environmental monitoring

Are fixed resistors and variable resistors interchangeable?

You could use a variable resistor in place of a fixed resistor as long as it’s able to provide the same resistance value. 

But, using a variable resistor in place of a fixed resistor is overkill as you are not using its full capabilities.

On the other hand, you cannot use a fixed resistor in place of a variable resistor as it cannot provide the same function (which is varying its resistance). 

Resistance values of fixed resistors

As you might know by now, resistors come in all shapes, sizes, materials, constructions, etc.

Resistance is an important variable when choosing a resistor. Every part of a circuit won’t necessarily require having a resistor of the same resistance value.

So, resistors come in a variety of resistance values. However, to avoid the confusion of allowing any resistance value under the sun, the resistances of resistors are organised into a set of preferred values or standard resistor values known as the E-series.

This enables you and me to choose resistors from a variety of different manufacturers while still having a consistent set of resistance values. 

The E-series defines a set of values within a certain decade (where the number next to the letter indicates the number of resistance values within that specific E-series)

For example, the E3 has a set of three resistance values; 1 ohm, 2.2 ohm and 4.7 ohm.

To get to the next decade, you would multiply a particular resistance value by 10. 

So, if we want to take the 1 ohm to the next decade’s value, we would multiply it by 10, which would give us a new resistance value of 10 ohms.

If however, you require a resistance value in the 1000s, you simply multiply the resistance value by a 1000 e.g; 1000 x 1 ohm  = 1000 ohms. 

You can do this for any of the resistances as long as it matches the value within the series. So, for the E3 series you are restricted to the three values of 1, 2.2 and 4.7.

Below are the other E-series available;

• E3
• E6
• E12
• E24
• E48
• E96
• E192

How to know the resistance of a fixed resistor?

Sooner or later, you are going to find a rogue resistor and unfortunately, resistors do not have their resistance values written on them. 

However, there is good news! 

While they might not have their resistance values written explicitly on them, resistors have bands of colours on them to help identify their resistance as well as their tolerances. 

This band of colours is known as the Resistor colour code.

Resistor colour codes can come in either a band of 4 or 5 colours.

Note, the last color band (tolerance value) is usually spaced apart further from the other colours so that there is no confusion when looking at the resistor from different points of view.

Below is a table of the colors associated with resistor color codes and their values.

The multiplier is the value you multiply the other numbers by to get the total resistance.

For example, let’s say we had a 4-band resistor with the colours, red, orange, yellow, and green.

• 1st digit = Red = 2
• 2nd digit = Orange = 3
• Multiplier = Yellow = 10⁴ (10000)
• Tolerance = Green = 0.5%

Therefore, the total resistance would be 23 x 10000 = 230000 ohms (or 230kohms), with a tolerance of 0.5%.

Another way of figuring out a resistor is to use a Multimeter, which has the ability to measure the resistance of materials (mainly conductors). 

Sometimes reading colour codes can be quite cumbersome, so using a multimeter might be the easier option.

Does a fixed resistor have constant resistance?

No, the resistance of a resistor is affected by Temperature.

The resistance increases as the temperature increases regardless of the material as well as the fixed length and area of the resistor (however, as we saw earlier, some fixed value resistors are more resistant to changes in temperature than others).

This happens because the atoms within a material get excited as the temperature increases. This causes the atoms to move about more hastily, making it harder for electrons to get through.

Superconductivity is a phenomenon whereby you subject conductors to extremely low temperatures, and almost eliminate all resistance of the conductor. 

The relationship between temperature and resistance can be summarized by the parameter known as Temperature Coefficient of Resistance (TCR). 

TCR shows the change in resistance as a function of the ambient temperature (this relationship is linear).

The post Difference between a fixed resistor and a variable resistor appeared first on Electronic Guidebook.

Along with these components, are many different terminologies such as capacitance, inductance, current, voltage, power, etc. 

You would be forgiven if you happened to confuse some of these components and terminologies. 

One very common confusion is between a Resistor and Resistance. 

Difference between a resistor and resistance

The difference between a resistor and resistance is that resistance is an electrical property that defines the ability of a component to ‘resist’ current. A Resistor is a component that is specifically designed to be able to limit current flow in electrical and electronic circuits. Resistors are created with a known resistance. 

So, the main difference between a resistor and resistance;

• Resistance is an electrical property that all components/ materials have,
• Resistors are components designed with a known resistance having the sole purpose of limiting current flow in circuits.

A deeper look resistance

It will help to learn about resistance and a resistor separately before taking a look at the difference between them. 

Let’s start with Resistance.

There are many instances of resistance outside the world of electronics. 

Think about a river. 

Imagine this river has no rocks so the water can flow at a steady pace with no interruptions. Now, let’s add some really big rocks. These rocks are going to provide a ‘resistance’ to the flow of water thereby slowing it down. 

Electrical resistance in electronics is very similar. It is a property of material that opposes (or resists) the flow of electrons (or current). 

The higher the resistance of the material, less current can flow, and the lower the resistance of the material, more current will be able to flow.

Materials can be classed into two categories; Conductors and Insulators.

Conductors are materials (such as gold, copper, aluminium, to name a few) that offer less resistance, therefore allow current to move more freely through them. This is why conductors are used to make wires and in the construction of electrical and electronic components.

Insulators on the other hand, are materials (such as glass, wood, plastic, etc) that have higher resistance and therefore inhibit the flow of current. In most cases no current can flow through them at all.

The discovery of resistance in electronics dates back to the early 1800s after a German physicist named George Simon Ohm learnt the relationship between Voltage, Current, and Resistance which he formulated into an equation known as Ohm’s Law.

These are three very important terminologies in the field of electronics (I would be surprised if you didn’t encounter any of them). 

Resistance is measured in Ohms named appropriately after the man who discovered it. 

Measuring the resistance of a given material

All materials are not made the same. As we saw above, some materials allow current to flow more freely (conductors), while others inhibit the flow of current (insulators).

But, all conductors do not have the same resistance. Resistance varies from one conductor to the next.

Lucky for us, there is an equation that enables us to calculate the resistance of conducting (and non-conducting) materials of given length and cross sectional area.

R = Resistance

p = Resistivity of material (temperature dependent) ( Ohm-meters) 

L = Length of material (m)

A = cross sectional area of material (m²)

Let’s take a look at an example of three different materials and compare their resistance. Since length, and area of materials affect the total end resistance, we shall assume the length and area to be the same for all three materials.

The three materials shall be Gold, Copper, and Wood (two conductors and one insulator).

Finding the resistivity of materials is as easy as googling; “resistivity of gold” to find the resistivity of a given material, or you could just google “resistivity of materials” which should yield a table of the resistivities of many materials. 

Resistivity of Gold = 2.44 x 10^-8

Resistivity of copper = 1.68 x 10^-8

Resistivity of wood = 10¹⁰ 

The Length for the three materials will be 20cm = 0.2m.

The Area for the three materials will be 15cm² = 0.0015m².

Note, when doing the calculations to find resistance, make sure your length and area values are in meters.

After using the equation, as well as the values for length, area, and resistivity, we get the following resistances for the different materials;

• Gold = 3.25 x 10^-6 ohms
• Copper = 2.24 x 10^-6 ohms
• Wood = 13.3 x 10¹¹ ohms

As you can see, the resistances of copper and gold are far lower than the resistance of wood.

This is the main reason you would use copper and gold circuits to allow current to flow, compared to wood (which wouldn’t let any current flow).

A deeper look at the resistor

Now that we know a bit more about resistance, let’s take a closer look at the Resistor. 

There are many different types of components and devices in the electrical and electronic world, each with their own unique abilities which help perform a certain function within a circuit. 

Components such as capacitors, transistors, inductors, integrated circuits, transformers, diodes, to name a few.

The Resistor is a fundamental electronic component that can be found in almost all circuits.

So what is the definition of a resistor? 

A resistor is a passive electrical and electronic component, whose main purpose is to ‘resist’ the flow of current in a circuit. Also, rather than having an ambiguous resistance value, resistors are created with a set resistance value. 

The bigger the resistance, the less current can flow, and the lower the resistance, the more current can flow.

It is known as a passive component due to the fact that it has no means of generating its own power, but rather dissipates power in the form of heat. 

The ability to resist current comes down to what we just learnt in the previous section about the resistance of materials, and how the resistor is constructed. 

Construction of a resistor and how it provides resistance

So, we know that conductors allow current to flow more freely compared to an insulator. 

Under the umbrella of resistors, there are many different variations of how they are constructed and the materials used. 

But, to save you time, I shall concentrate on the most common type which is the Wire-wound (other forms of the resistor shall be discussed later if you do want to learn a bit more).

Below is an image of what a wire-wound resistor looks like on the inside;

As you can see, there is a rod that is wrapped by a wire. The rod is typically an insulating ceramic, and the wire is copper (due to its great conductivity)

But, copper has low resistance! So, why use it in a component meant to resist the flow of current?

While resistors need to oppose the flow of current, they still need to let the current pass. But, just sticking a straight piece of copper wire inside a resistor is not going to add much resistance. 

The key to increasing the resistance of a set length of copper wire comes down to coiling the wire. This is why the copper wire is wound (coiled) around the insulating material.

The resistance of a resistor can be accurately set by controlling the number of turns of the coil of copper wire (resistors come in a number of different resistance values, which I will talk about in more depth later). 

Also, we saw the resistance of a material is controlled by a number of factors; length and cross-sectional area.

If the length of copper wire is set, we can further increase its resistance after coiling it by reducing its cross-sectional area (make it thinner). This is thanks to the inversely-proportional relationship between resistance and the cross-sectional area of a wire.

But, what if you want to reduce the resistance of a resistor?

Just do the opposite! Reduce the number of turns, and increase the cross-sectional area of the wire. 

What is the difference between a resistor and resistance?

Alright, so we have had a quick look at both resistance and a resistor individually. You might have already got the jist of the differences between the two. 

But, just in case you are still unsure, I will explain the main difference. 

When we talk about electrical resistance, as we saw earlier, we are talking about a material’s ability to resist the flow of electrons (current). 

All materials have electrical resistance,some have lower resistance (conductors) compared to others which have higher resistance (insulators).

Now, a resistor is an electrical component which is specifically designed to have a set value of resistance. 

So, the main difference is that electrical resistance is a property that all materials have, and a resistor is a component that is designed with the specific purpose of implementing resistance in electrical and electronic circuits. 

Sometimes these words can be used interchangeably and might be the reason you could be confused. 

For example, you could say I require a resistor of 10 ohms, or a resistance of 10 ohms when designing a specific type of circuit. 

Why are resistors important in electronics

But, why do we need resistors in the first place? 

Every electrical and electronic component has something known as a Power Rating.

This is a value that indicates how much electrical power is needed by the component to work effectively. 

Also, the power rating value indicates the maximum allowable electrical power the device or component can handle.

Exceeding this value will cause damage to the component. 

The power rating can be broken further into; Voltage ratings, and Current ratings. 

This is because power is a product of voltage and current ( P = V x I).

Components will have values for maximum voltage and maximum current ratings that should not be exceeded.

Resistors are important as they allow us to protect components in circuits by limiting the current so that the current ratings of that component are not exceeded (and therefore power rating as well).

Sometimes you might not be able to change the power supply (which means the voltage is fixed), so you will need a resistor to limit the other variable in the power equation (in this instance the current).

Different types of resistors and their resistances

There isn’t one specific type of resistor. Resistors primarily fall under two categories; Fixed value resistor and Variable resistors. 

Each offers a range of resistance values. Let’s take a deeper look at both types. 

Resistors with fixed value resistance

As the name might suggest, fixed value resistors have a resistance that is fixed regardless if there is a change in voltage.

It cannot physically change its resistance. 

For example, if you bought a 10 ohm fixed value resistor, this is the only resistance that the resistor is going to be able to provide.

In an ideal world, the resistor would provide a fixed resistance at all times. However this is not the case, as their resistance varies slightly with temperature (which we shall look at later). 

Fixed value resistors are the most commonly used in circuits. Their value is chosen during the circuit design phase using calculations such as ohm’s law. 

Earlier we saw the construction of a wire-wound resistor. This is one of the most common fixed value resistors.

However, there are many other types of fixed value resistor available;

• Carbon composition 
• Carbon film
• Metal Film
• Metal-oxide film 
• Metal glaze
• Foil

Carbon composition fixed value resistors

Have a cylindrical form with metal caps at either end of the cylinder. Inside the cylinder is a substance that is a mixture of carbon power and ceramic. 

While used primarily in the early 1960’s, this type of fixed value resistor isn’t used a lot anymore due to its high cost and low stability. 

Carbon film fixed value resistors

Has a very similar construction to the carbon composition resistor. However, a carbon film is placed atop a ceramic substrate. 

This type of fixed value resistor produces less noise when compared to carbon composition resistors. 

Metal film fixed value resistors

The metal film resistor has the same construction as the carbon film. But, rather than using carbon as the material of the film, other metals are used.

Metals used in metal film resistors are usually Nickel Chromium, Tin or Antimony.

The resistance of metal film is less affected by temperature. 

Metal oxide fixed value resistors

Has the same construction as carbon film, and metal film resistors.Again, what sets them apart is the material used. 

The film in this resistor is a metal oxide such as Tin Oxide.

They cost less compared to carbon composition resistors, and can be used at higher temperatures. 

Metal glaze fixed value resistors

Use a composition of glass powder and metal particles to restrict the flow of current.

Its resistance is also less affected by temperature. 

Foil fixed value resistors

Last but not least are foil resistors. 

They are made using an alloy (a material composed of two or more metallic elements). The foil is created from an alloy of nickel and chromium. 

Of all the different types of construction for fixed value resistors, these are the most accurate and stable. They also produce far less noise. 

Resistors that can vary their resistance

The next major type of resistor is the Variable Resistor.

This type of resistor has the ability to vary its resistance between two set values (with the lower usually being 0 ohms).

Note, this does not mean it’s restricted to those values, it can have a range of values which sit within the range of its lower and upper resistance limits. Its incremental value depends on the resolution of the variable resistor. 

For example if you have a 10k variable resistor, you would be able to set its resistance at any value between 0 and 10k ohm. So, you could set it at 10, 100, 1k, 2.5k, 5.7k, 8k etc. 

Below are the most commonly used circuit symbols for variable resistors;

The construction of a variable resistor is basically a fixed resistive element along with a wiper that sits on the resistive element. 

The slider can be adjusted (by means of a slider or knob which you control) to sit anywhere along the resistive element thereby adjusting the overall output resistance. 

As you can see there are three terminals and the resistive element is connected to terminals 1 and 3. To use it as a variable resistor, you have to make connections to terminal 1 and 3.

The great thing about the variable resistor is that it has an added ability, which is to vary voltage. When used to vary voltage, it is known as a Potentiometer.

To use it as a potentiometer, you would connect terminals 1 and 3 to GND and VCC (it doesn’t matter which terminal gets connected to what). The varied voltage is then presented at terminal 2. 

Other forms of the variable resistor

The variable resistor we just looked at is just one of the most common types which varies its resistance mechanically (twisting a knob, or moving a slider).

However, there are other forms of variable resistors each having its own unique way of varying resistance. 

Let’s take a quick look at each of them. 

Light dependent resistors

The  first on the list are Light Dependent Resistors (LDRs).

However, they have many other aliases that you might know it by, which include, Photoresistor, Photocell, or Photoconductor. 

The resistance of light dependent resistors changes depending on varying light levels. The amount of resistance that changes depends on the intensity of light, as well as the sensitivity of the LDR.

The less light that the LDR is subject to, the higher its resistance (in the order of megaohms) and the more light that shines upon the LDR, the lower its resistance (few hundred ohms).

They are created using a semiconducting material that gives them their light sensing abilities. 

Common applications of the light dependent resistors;

• Smoke alarms
• Photographic light meters
• Streetlights 
• Burglar alarms

Force sensitive resistor

Next up we have the Force Sensitive Resistor (FSR).

The resistance of the force sensitive resistor changes when it is subject to force, pressure or weight. 

How much the resistance changes is proportional to the amount of force being applied. 

When there is no force applied to them, it has an almost infinite resistance (which can be viewed as an open circuit).

When a light force is applied, the resistance ranges around 100kohm.

At maximum force, the resistance can be as low as 200 ohm. 

Note, these values will vary from one FSR to the next. 

FSRs can withstand forces up to 20lb (roughly 100 Newtons). 

Common applications of force sensitive resistors;

• Midi controllers (for music producing)
• Electronic drum kits
• Electronic throttle and brake (automotive)
• Gaming joysticks 
• Sports (target force and accuracy detection)

Thermistor

The Thermistor is a portmanteau of the words ‘thermal and ‘resistor’.

These words are chosen because of the fact that the thermistor is a device whose resistance varies depending on ambient temperature. 

There are two types of thermistor; Negative temperature coefficient (NTC) and Positive temperature coefficient (PTC).

The relationship between resistance and temperature in NTC thermistors is inversely proportional. This means as temperature rises, resistance decreases, and vice versa.

In PTC thermistors, the relationship between resistance and temperature is proportional. So, when temperature rises, so does the resistance, and vice versa.

Common applications of thermistors; 

• Fire alarms
• Refrigerators 
• Ovens
• Digital thermometer
• Automotive applications 

Humistor

Last but not least is the humble Humistor.

The humistor is a combination of the words ‘humidity’ and ‘resistor’.

The resistance of this electronic device varies depending on humidity levels. 

Humidity is the amount of water vapour present in the air. The resistance of the humistor depends on the total amount of water vapour molecules it absorbs.

As humidity increases, the amount of water molecules absorbed by the humistor increases thus causing it to be more conductive which results in its resistance decreasing. 

On the other hand, the less water molecules absorbed, causes the humistor to be less conductive thereby increasing its resistance. 

Common applications of the Humistor;

• Agriculture
• Textile factories (where humidity can affect materials)
• Refrigerators
• Atmospheric environmental monitoring

Resistance values of a resistor

As you might know by now, resistors come in all shapes, sizes, materials, constructions, etc.

Resistance is an important variable when choosing a resistor. Every part of a circuit won’t necessarily require having a resistor of the same resistance value.

So, resistors come in a variety of resistance values. However, to avoid the confusion of allowing any resistance value under the sun, the resistances of resistors are organised into a set of preferred values or standard resistor values known as the E-series.

This enables you and me to choose resistors from a variety of different manufacturers while still having a consistent set of resistance values. 

The E-series defines a set of values within a certain decade (where the number next to the letter indicates the number of resistance values within that specific E-series)

For example, the E3 has a set of three resistance values; 1 ohm, 2.2 ohm and 4.7 ohm.

To get to the next decade, you would multiply a particular resistance value by 10. 

So, if we want to take the 1 ohm to the next decade’s value, we would multiply it by 10, which would give us a new resistance value of 10 ohms.

If however, you require a resistance value in the 1000s, you simply multiply the resistance value by a 1000 e.g; 1000 x 1 ohm  = 1000 ohms. 

You can do this for any of the resistances as long as it matches the value within the series. So, for the E3 series you are restricted to the three values of 1, 2.2 and 4.7.

Below are the other E-series available;

• E3
• E6
• E12
• E24
• E48
• E96
• E192

How to find out the resistance of a resistor?

Sooner or later, you are going to find a rogue resistor and unfortunately, resistors do not have their resistance values written on them. 

However, there is good news! 

While they might not have their resistance values written explicitly on them, resistors have bands of colours on them to help identify their resistance as well as their tolerances. 

This band of colours is known as the Resistor colour code.

Resistor colour codes can come in either a band of 4 or 5 colours.

Note, the last color band (tolerance value) is usually spaced apart further from the other colours so that there is no confusion when looking at the resistor from different points of view.

Below is a table of the colors associated with resistor color codes and their values.

The multiplier is the value you multiply the other numbers by to get the total resistance.

For example, let’s say we had a 4-band resistor with the colours, red, orange, yellow, and green.

• 1st digit = Red = 2
• 2nd digit = Orange = 3
• Multiplier = Yellow = 10⁴ (10000)
• Tolerance = Green = 0.5%

Therefore, the total resistance would be 23 x 10000 = 230000 ohms (or 230kohms), with a tolerance of 0.5%.

Another way of figuring out a resistor is to use a Multimeter, which has the ability to measure the resistance of materials (mainly conductors). 

Sometimes reading colour codes can be quite cumbersome, so using a multimeter might be the easier option.

Are resistors the only components that have resistance?

No, every component has some sort of resistance. As we saw earlier, all materials have resistance depending on the type of material as well as their length and area.

However, they are not specifically designed to have a certain amount of resistance like resistors are. The resistance values are random.

When designing circuits, the total resistance needs to be taken into consideration. Most of the time, the total resistance of components (other than resistors), can be small enough that they won’t affect the overall resistance of the circuit. 

Does a resistor have constant resistance?

No, the resistance of a resistor is affected by Temperature.

The resistance increases as the temperature increases regardless of the material as well as the fixed length and area of the resistor (however, as we saw earlier, some fixed value resistors are more resistant to changes in temperature than others).

This happens because the atoms within a material get excited as the temperature increases. This causes the atoms to move about more hastily, making it harder for electrons to get through.

Superconductivity is a phenomenon whereby you subject conductors to extremely low temperatures, and almost eliminate all resistance of the conductor. 

The relationship between temperature and resistance can be summarized by the parameter known as Temperature Coefficient of Resistance (TCR). 

TCR shows the change in resistance as a function of the ambient temperature (this relationship is linear).

The post Difference between a resistor and resistance appeared first on Electronic Guidebook.