PWM motor speed controller

This circuit is designed as per a request made by Mr Vinoth from India. His requirement was a 12V/5A DC fan motor controller. I think this circuit is sufficient for this purpose. Quad 2 input Schmitt trigger IC CD4093 is the heart of this circuit. Out of the four Schmitt triggers inside the 4093, U1a is wired as an oscillator with adjustable duty cycle. The U1b, U1c, U1d buffers the output of the oscillator to drive the switching MOSFET Q1.The MOSFET drives the DC motor according to the switching pulse obtained from the oscillator. When R1 is varied the duty cycle varies and so do the speed of the motor. Diode D3 acts as a freewheeling diode.

Circuit diagram with Parts list.


  • Assemble the circuit on a good quality PCB.
  • IC U1 should be mounted on a holder.
  • U1a, U1b, U1c, U1d are part of the same IC CD4093; so power supply is shown connected only once.
  • The12V power supply for this circuit must be able to handle at least 5A.
  • A heat sink is recommended for Q1.