PWM Motor Controller

Speed control for DC motors using PWM

Note: This circuit is designed for small to medium DC motors. For high-power motors, additional components for heat management and filtering may be required.

Circuit Description

This Pulse Width Modulation (PWM) motor controller circuit provides variable speed control for DC motors. By using the popular 555 timer IC configured as an astable multivibrator, it generates a PWM signal that can efficiently control motor speed without excessive power loss.

How It Works

The circuit operates on the principle of Pulse Width Modulation (PWM), where the power delivered to the motor is controlled by rapidly switching it on and off. The 555 timer generates a square wave with adjustable duty cycle (controlled by the potentiometer). The MOSFET or transistor acts as a switch, delivering power to the motor only during the "on" portions of the cycle. The average power delivered is proportional to the duty cycle, giving smooth speed control.

Circuit Schematic

Components List

1 × 555 timer IC
1 × IRFZ44N N-channel MOSFET (or similar)
1 × 1N4007 diode (freewheeling diode)
1 × 10kΩ resistor (R1)
1 × 1kΩ resistor (R2, gate resistor)
1 × 10kΩ potentiometer (speed control)
1 × 0.1μF ceramic capacitor (C1)
1 × 0.01μF ceramic capacitor (optional, for pin 5)
1 × DC motor (12V or lower, depending on your power supply)
1 × Breadboard or PCB
1 × 12V power supply (appropriate for your motor)
Jumper wires
Heat sink for MOSFET (for motors over 1A)

Installation Instructions

Place the 555 timer IC on your breadboard, ensuring proper orientation.
Connect pin 1 (GND) of the 555 timer to the ground rail.
Connect pin 8 (VCC) and pin 4 (RESET) to the positive power rail.
Connect the 0.1μF capacitor (C1) between pin 2 (TRIGGER) and ground.
Connect pin 2 (TRIGGER) to pin 6 (THRESHOLD).
Connect the 10kΩ resistor (R1) from the positive rail to pin 7 (DISCHARGE).
Connect pin 7 (DISCHARGE) to pin 6 (THRESHOLD).
Connect the 10kΩ potentiometer with one end to the positive rail, the other end to pin 7 (DISCHARGE), and the wiper to pin 6 (THRESHOLD).
Connect an optional 0.01μF capacitor from pin 5 (CONTROL) to ground for stability.
Connect the 1kΩ resistor (R2) from pin 3 (OUTPUT) to the gate of the MOSFET.
Connect the source of the MOSFET to ground and the drain to one terminal of the motor.
Connect the other terminal of the motor to the positive power rail.
Connect the 1N4007 diode across the motor terminals (cathode to positive rail) to protect against back EMF.
If the MOSFET will be handling more than 1A, attach a heat sink.
Connect your power supply to the power rails.
Test the circuit by adjusting the potentiometer to control the motor speed.

Troubleshooting Tips

Motor doesn't run: Check all connections, ensure the MOSFET is properly oriented, and verify your power supply has sufficient current capability.
Motor runs at full speed only: Check the connections to the potentiometer and timing capacitor.
Motor speed control is too coarse: Try a different value potentiometer or adjust the timing capacitor value.
MOSFET gets hot: Add a heat sink or switch to a MOSFET with lower Rds(on) resistance.
Circuit works but makes noise: Add additional filtering capacitors across the power supply rails.