Circuit Description

Here is the circuit diagram of PWM motor speed controller. The application of this circuit lies in the speed control of low power DC motors. The core part of this circuit is the IC CD40106B in which the gates N1 and N2 are used in this circuit as shown in figure. The speed control action is accomplished by varying the duty cycle of the pulse which is used for driving the motor. The gates N1 and N2 play different roles in this circuit. Here N1 works as inverting Schmitt Trigger astable multi vibrator which produces pulses where as N2 works as inverting buffer to drive the transistor during positive cycles at base. The duty cycle of the pulses is adjusted by means of the potentiometer R2 (100K). The base current of transistor Q1 (SL 100) is limited by the resistor R1 (22K).

Circuit Diagram

PWM Motor Speed Controller
PWM Motor Speed Controller


  • This circuit is ideal for controlling toy motors, hand held mini fans, small blowers etc.
  • Duty cycle of pulse can be varied from 0% to 100% by adjusting potentiometer R2.
  • In transistor SL 100, the pin connected to casing is collector, the pin near to notch is emitter and the one remaining is base.