Motor Circuit Diagrams

Speed Control of DC Motor Using Pulse Width Modulation


  • Introduction
  • How Speed Control of DC Motor is implemented?
  • Circuit Diagram of PWM Based DC Motor Speed Control
  • Components Required 
  • Circuit Design
  • How Speed Control of DC Motor Circuit Works?


In this project, I will show How Speed Control of DC Motor can be implemented using 555 and Pulse Width Modulation (PWM).

In our daily lives, we employ DC Motors in a variety of devices. CPU fans, fire extinguishers, and toy vehicles, for example, are all DC Motors that are powered by a DC power supply. Most of the time, we’ll have to change the motors’ speed to meet our needs.

When the CPU is performing heavy duties like games or video editing, the CPU Fan, for example, must run at a high speed. The fan’s speed can be lowered for routine use, such as editing papers.

Although some systems offer an automatic fan speed adjustment system, this feature is not available on all systems. As a result, we’ll have to manually modify the DC Motor’s speed from time to time.

How Speed Control of DC Motor is implemented?

There are multiple ways to adjust the speed of a DC Motor manually. The simplest way to achieve this is with the help of a variable resistor i.e. we can adjust the speed of a DC Motor by using a variable resistance in series with the motor.

But this method is usually not prepared for two reasons. The first reason is energy wastage i.e. the resistor dissipates the excess energy as heat. The second reason is if we want to use any devices like microcontrollers or any other digital equipment for automating our DC Motor speed control, then this method cannot be used. 

A more efficient way to proceed is by using Pulse Width Modulation technique to Control the speed of our DC motor.

Circuit Diagram of PWM Based DC Motor Speed Control

Components Required 

  • 555 Timer IC 
  • 12V DC Motor 
  • 1N5819 x 2 
  • 1N4007 
  • 100nF 
  • 100pF 
  • 10KΩ Resistor 
  • 100KΩ Potentiometer 
  • IRF540 MOSFET 
  • Mini Breadboard
  • 12V Power Supply 
  • Connecting Wires

Circuit Design

I’m not going to go into the 555 IC’s pin diagram because I’m assuming you’re already familiar with it. Continuing with the circuit design, Pin 1 of the 555 is connected to GND. +12V Supply is linked to Pins 8 and 4.

Pins 6 and 2 are short, and Pin 2 is connected to GND via a 100nF capacitor. The POT’s wiper pin is connected to the 555’s Pin 3. As illustrated in the circuit schematic, two Schottky diodes (1N5819) are connected to the POT’s other two pins.

Pin 2 is connected to the diodes’ common point. With the help of a 10K resistor, Pin 7 is pulled high. Pin 7 of the 555 is connected to the MOSFET’s Gate terminal. The MO’s +12V Supply and Drain are linked to the motor.

A PN Junction Diode is connected across the Motor terminals to prevent the back emf. 

NOTE: I haven’t used the Schottky Diodes but replaced them with simple 1N4007 Diodes as the frequency of the PWM is less (around 220Hz). 

Speed Control of DC Motor

How Speed Control of DC Motor Circuit Works?

In this circuit, the DC motor is operated by a 555 integrated circuit. The IC 555 in this circuit is being operated in astable mode, which produces a continuous HIGH and LOW pulses. 

In this mode, the 555 IC can be used as a pulse width modulator with a few small adjustments to the circuit. The frequency of operation of the circuit is provided by the passive parameters of resistances and capacitors attached to it.


  • One of the best things about this circuit is that it can be made to work as an astable multivibrator with very little hardware and very little money, saving both money and space on the printed circuit board (PCB).
  • A microcontroller-based pulse width modulator is preferable to the one we’re using currently if you want a more complex pulse width modulator that operates more accurately and has more adjusting possibilities.
  • The circuit or application for which we are employing a pulse width modulator, on the other hand, is not as sensitive and so does not require as much precision. In this scenario, the circuit we’re employing with a bare IC 555 is ideal.
  • The duty cycle of the circuit can be changed by changing the value of the potentiometer. If we increase the duty cycle, the speed of the motor increases and if we decrease the duty cycle, the speed of the motor decreases.


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