Resistors play a key role in almost every electronic circuit. Some important resistor functions in circuits are – they limit the current flow through the circuit, protect the circuit from overcurrent flow, voltage division, feedback, Gain control, pulling up or pulling down the floating voltages, and much more.
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Don’t be confused about the above terms used. Because in the rest of the article, I will explain them.
So, let’s explore some fundamental functions and roles of a resistor in electronic circuits.
Resistor Functions in Circuits
A resistor offers resistance to current flow through it. It is the most used component both in electrical and electronics circuits.
The above is a circuit symbol and some physical resistors.
Current Limiter
The resistance value of the resistor determines the amount of current that can easily flow through the resistor to the rest of the component or circuit.
Hence, the value of the resistor for a fixed resistor is fixed, which means that the amount of current is fixed.
So, if you don’t want a current amount to exceed a certain value in your circuit. Then use a resistor with a resistance value respective accordingly using Ohm’s Law.
Circuit Protection
The above current limitation is very useful for protecting the circuit from overcurrent flow. So, we can say that one of the resistor functions in a circuit is actually to protect the circuit.
For protection purposes, a resistor in series connection is added to the circuit block or component.
You can say a resistor is like a fuse. It burns itself, but it protects the rest of the circuit. And that’s the reason you will encounter a lot of resistors in front of various expensive circuit elements.
Voltage Division
Sometimes we need multiple voltage levels in one signal circuit. The issue is, that we can not put different values’ power sources.
If we do the above, you can imagine our circuits and product will be bulky, heavy, and with limited styling. And most importantly, very efficient in the long run.
So, we use resistors in voltage divider configuration to achieve different voltage levels according to the requirements of our circuit.
Remember, voltage division is best used for small values and powering small devices. You should not expect it to use for heavy currents, as it is not designed for this purpose.
Voltage referencing
The voltage reference is a pre-set constant value to which we compare our other values, or use it as a state.
The voltage reference is a very important concept and plays a key role in digital circuits.
We use the above voltage division circuits to make voltage levels which we use for reference purposes in our circuits.
Feedback
Feedback term is mostly used when we are working with operational amplifiers, shortly op-amps. We use this concept in other circuits as well.
Operational amplifiers have an open gain in thousands (sometimes even more) which makes them easily saturated.
To control this gain of an op-amp, we use resistors in a feedback mechanism. Feedback may be negative or positive, depending on the goal of the circuit.
Feedback is created when you connect the output of a circuit back to the input of the same circuit. This circuit looks like a loop that brings the output to the input and sees if there is an error.
Gain Control
Gain is an added value to the coming input signal by a circuit element or block. Like if you are designing an amplifier with a gain of 1000. The input to this amplifier is 10mV. So, at the output of this amplifier, you will have 0.0001×1000, i.e. 1V
Resistors are used to help us set this gain value for the amplifier using the guidelines of positive or negative feedback.
Gain control is very important. The value of gain determines the scope and manufacturing cost of the circuit.
Handling Floating Voltages
Floating is a very common phenomenon in microcontrollers when a pin is left open or unused.
For example, you have a microcontroller (MCU) with one pin configured as an input.
If there is nothing connected to the pin and your program reads the state of the pin, will it be high (pulled to VCC) or low (pulled to ground)? It is difficult to tell. This phenomenon is referred to as floating.
To prevent this unknown state, a pull-up or pull-down resistor will ensure that the pin is in either a high or low state, while also using a low amount of current.
Signal Levels Adjusting
Sometimes we need to adjust the level of signals so that they align with the requirements of other components, or other blocks of a circuit.
In simple words, let’s say you have a signal on the y=0 line, but the requirement is to adjust it to the y=3 line.
In the said situation, we use resistors in different configurations to achieve the above.
Load Termination
Load termination means to terminate or close a circuit with some output. Usually, when we are designing circuits, we are designing for certain output values.
To precisely get those output values, we use resistors as loads to terminate our circuits, so we can verify our results.
For example, you want to output the current to be 2Amp. To verify it, you will connect a resistor load according to said value and see the performance of your circuit.
Resistor load termination is very helpful especially when we are working with high-frequency circuits, i.e. RF circuits.
Concluding resistor functions in circuits
Resistors are the most fundamental components which may see in every electronics circuit. The reason why it is so used in circuits is that it offers so many useful functions.
Following is the summary of some resistor functions in electronics and electrical circuits:
- Current Limiter
- Circuit Protection
- Voltage Division
- Voltage referencing
- Feedback
- Gain Control
- Handling Floating Voltages
- Signal Levels Adjusting
- Load Termination
In this article, we try to explore some key resistor functions in circuits. Of course, I am not perfect, nor this article is. This is just my limited knowledge try to help you somehow.
I hope you enjoyed this article.
Thank you so much and have a grateful and valuable life.
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Thanks Abbas!