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 demonstrate the implementation of speed control for DC motors using a 555 timer and Pulse Width Modulation (PWM).

DC motors find extensive use in various devices in our daily lives, such as CPU fans, fire extinguishers, and toy vehicles. These motors are typically powered by a DC power supply. Often, we need to adjust the speed of these motors to suit specific requirements.

For instance, when a CPU is engaged in demanding tasks like gaming or video editing, the CPU fan needs to operate at a high speed to maintain optimal temperature. However, during routine tasks like word processing, reducing the fan speed is both energy-efficient and less noisy.

While certain systems offer automated fan speed adjustment, not all systems come equipped with this feature. Therefore, there are instances when we need to manually modify the speed of a DC motor.

How Speed Control of DC Motor is implemented?

There are several methods for manually adjusting the speed of a DC motor. The most straightforward approach is to utilize a variable resistor, where we can regulate the motor’s speed by introducing a variable resistance in series with it.

However, this method is often deemed less desirable for two primary reasons. Firstly, it results in energy wastage as the resistor dissipates excess energy in the form of heat. Secondly, if we intend to incorporate devices like microcontrollers or other digital equipment for automated DC motor speed control, this method becomes impractical.

A more efficient and versatile approach is to employ Pulse Width Modulation (PWM) techniques 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 won’t delve into the pin diagram of the 555 IC since I assume you’re already acquainted with it. Continuing with the circuit design, Pin 1 of the 555 is connected to the ground (GND). The +12V supply is connected to Pins 8 and 4.

Pins 6 and 2 are shorted together, and Pin 2 is linked to GND through a 100nF capacitor. The wiper pin of the POT is connected to Pin 3 of the 555. As shown in the circuit diagram, two Schottky diodes (1N5819) are connected to the other two pins of the POT.

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

A PN Junction Diode is placed across the motor terminals to prevent back electromotive force (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?

This circuit utilizes a 555 integrated circuit to control the DC motor. The IC 555 in this configuration is set to operate in astable mode, generating continuous HIGH and LOW pulses.

In this mode, with some minor modifications to the circuit, the 555 IC can function as a pulse width modulator. The circuit’s operating frequency is determined by the passive components, namely the resistors and capacitors connected 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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