Pulse Width Modulation DC Motor Control

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 1 Meg 1/4W Resistor R2 1 100K Pot C1 1 0.1uF 25V Ceramic Disc Capacitor C2 1 0.01uF 25V Ceramic Disc Capacitor Q1 1 IRF511 MOSFET IRF620 U1 1 4011 CMOS NAND Gate S1 1 DPDT Switch M1 1 Motor (See Notes) MISC 1 Case, Board, Heatsink, Knob For R2, Socket For U1

Notes

1. R2 adjusts the speed of the oscillator and therefore the speed of M1.
2. M1 can be any DC motor that operates from 6V and does not draw more than the maximum current of Q1. The voltage can be increased by connecting the higher voltage to the switch instead of the 6V that powers the oscillator. Be sure not to exceed the power rating of Q1 if you do this.
3. Q1 will need a heatsink.
4. Q1 in the parts list can handle a maximum of 5A. Use the IRF620 for 6A, if you need any higher.
5. This circuit is not a true pulse width modulation control. Because only the frequency of pulses varies, it is really pulse frequencymodulation. This works, though not as well as true PWM.