PWM DC Motor Speed Controller

Pulse Width Modulation (PWM) controllers efficiently control the power delivered to a load by adjusting the width of the pulses in a signal to change the voltage and current without wasting energy. This 555 PWM controller can drive a DC motor of up to 80W.

Components List

The following components are required to make this project.

Designation	Parts	Quantity
U1	IC NE555 Timer	X1
R1	1kΩ 1/4W Resistor	X1
R2	50kΩ Potentiometer	X1
R3	220Ω 1/4W Resistor	X1
C1	1nF Ceramic Capacitor	X1
C2	100nF Ceramic Capacitor	X1
D1, D2	1N4001 Diode	X2
D3	SR560 Schottky Rectifier Diode	X2
Q1	IRFZ44N N-Channel Power MOSFET	X1
MOT1	DC Motor 80-Watt Max.	X1

Circuit Diagram

Schematic of PWM DC motor speed controller circuit using IC 555 timer is shown below.

Circuit Explanation

The 555 timer (U1) in astable mode generates a continuous square wave signal, which can vary in frequency from 14 kHz to 1.44 MHz. When a power supply between +6V and +28V is connected, the capacitor C1 begins to charge through resistor R1, potentiometer R2, and diode D1.

As the capacitor charges, its voltage increases. When the voltage across the capacitor reaches two-thirds of the supply voltage, the threshold pin (pin 6) of the 555 timer detects this change, causing the output pin (pin 3) to switch from HIGH to LOW. At this point, the capacitor discharges through potentiometer R2 and diode D2 into the discharge pin (pin 7).

As the capacitor discharges, the voltage across it drops. When the voltage falls to one-third of the supply voltage, the trigger pin (pin 2) detects this and switches the output pin (pin 3) back to HIGH. This cycle repeats, producing a square wave output that toggles between HIGH and LOW. A capacitor C2 is placed between control pin (pin 5) and ground to filter out noise and provide stability.

This PWM signal is sent through resistor R3 to the gate of a MOSFET (Q1), turning the DC motor ON and OFF. The speed of the motor can be controlled by adjusting the duty cycle using potentiometer R2. Additionally, a flyback diode is connected in parallel with the DC motor to protect the circuit from back EMF when the motor turns off.