Pulse Width Modulation[PWM] Working, Applications, Advantages

Pulse Width Modulation[PWM]

Pulse Width Modulation is a technique of creating modulated electronic pulses or electronic pulses of the desired width. The Pulse Width Modulation(PWM) technique has become popular and is used in many analog electronic devices and also in Power Electronics. In this post, we are going to learn workings, applications, and advantages of Pulse Width Modulation(PWM).

Actually, if you have clear basic knowledge about the 'Electronic Pulse' then you will understand easily Pulse Width Modulation(PWM).

So let's start from the basics.

What is an Electronic Pulse?

As we cannot see the electricity visually so we use waveforms, various types of signs, etc only to understand the electrical concepts theoretically. Electronic Pulse is nothing but a graphical representation of the nature of the flow of current in an electrical or electronic circuit.

For example, an LED is connected to a battery through a switch. We keep the switch ON for 2 sec and keep the switch OFF for 2 sec and the process remains repeating. Now the nature of the flow of current from the battery to the LED can be shown by a Pulse Wave Form.

As we are going to do modulation of the width of electronic pulses, so first let's know what is the width of the pulse?

The pulse signal represents that the supply is ON for a certain time and the supply is OFF for a certain time. The ON condition is also called that the signal is high and the OFF condition is also called that the signal is low. The time during which the signal is high can be represented by the width of the pulse. In the below figure width, amplitude etc shown.

What is Pulse Width Modulation?

The changing(increase or decrease) of the width of an electronic pulse according to our requirement is called Pulse Width Modulation.

By the Pulse Width Modulation(PWM) technique, we can decrease or increase the width of the electronic pulse.

Why we need Pulse Width Modulation?

To understand the need of the pulse width modulation we must know what is the difference between a pulse signal and a continuous signal.

click on the image to enlarge

In the above figure, a continuous DC signal and a pulse DC signal are shown. Both of the signals have the same peak value which is 12V. The pulse signal has a 50% duty cycle. Now if we connect a load with the continuous DC source then the load will get full 12V, but if we connect that load with the pulsed DC source the load will get only 6V. Because of the average value of the pulse DC is only 6V at 50% duty cycle.

Now if we decrease the duty cycle to 25% then the average value of the pulse will be 3V. So it is clear that the average value of the pulse signal depends upon the duty cycle.

You may have a question in your mind that what is Duty Cycle?

The duty cycle is the time during which the pulse is active or the signal is high with respect to the total time period.

•  If the signal is high for 2 sec and low for 2 sec then it is called that the signal has a 50% duty cycle and the time period is 4 sec. 
• If the signal is high for 1 sec and low for 3 sec then the duty cycle will be 25% and time period will be 4sec.
• If the signal is high for 3 sec and low for 1 sec then the duty cycle will be 75% and time period will be 4sec.

So the average value of the pulse signal depends upon the duty cycle and the duty cycle depends on the Width of the pulse. So by the technique of the pulse width modulation, we can control the average value of the signal.

Understand the PWM with an Example:

Suppose we want to control the speed of a 24V DC motor. We know that the speed of the DC motor can be controlled by controlling the applied voltage. Now if we apply the PWM on the motor and vary the width of the pulses, the duty cycle also be varied and the average value will change according to the duty cycle, therefore, the speed will be changed according to the average value.

So the pulse width modulation technique is nothing but the control of the average value of a power supply.

The frequency in the Pulse Width Modulation technique has a very important role. The frequency is defined as the no. cycles per second. When we use PWM for the dimming of light, then if we use high frequency we feel like that the light is not dimming, but if we use low frequency then we see the dimming of light very clearly.

There are different frequencies are used for different applications.

How to generate DC PWM Signal:

The generation of a DC PWM signal is very simple. Using a Comparator we can generate a PWM signal. To generate a PWM signal we have to need two signals one is a triangular wave and another is DC supply which can be controlled at any time. Now if we apply the triangular wave and control DC voltage to a comparator together then we will get the PWM signal from the output of the comparator.

click on the image to enlarge

As you see in the above diagram when the voltage of the triangular wave is less than the controlled DC voltage then the output of the comparator will be low but when the voltage of the triangular wave is greater than the controlled DC voltage the output of the comparator will be high.

So we can control the width of the pulses by controlling the DC voltage and we control the frequency of the pulses by controlling the triangular wave. When we reduce the value of the DC voltage, the width of the pulses will be increased and if we increase the value of the DC voltage, the width of the pulses will be decreased.

How to generate AC PWM Signal:

The generation of AC PWM signal is the same as the generation of a DC PWM signal only difference is that we need to give a sinusoidal AC supply instead of DC supply. By controlling the sinusoidal AC voltage we can control the width of the pulses.

Generation of PWM Signals using IC 555:

We can generate the PWM signal using IC 555. The circuit diagram is given below. By varying the value of R1 we can control the duty cycle or width of the pulses.

Advantages of Pulse Width Modulation:

1.    Low Power Loss

2.    High efficiency.

3.    Easy to use.

4.    The circuits need a smaller area.

5.    Low initial cost as well as maintenance cost.

Applications of Pulse Width Modulation:

1.    In modern days, the Pulse Width Modulation technique is used to control the speed of the motors in Industries.

2.    Pulse Width Modulation is used for dimming light.

3.    PWM is used to control the electrical power.

4.    PWM is used in communication systems also.

5.    PWM is used in the Audio system.

6.    In modern Inverters, the PWM is used.

7.    Using the PWM technique and the switching mechanism we can control analog signals using the digital signal.

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