The DC motor speed control circuit is designed using IC LM3578 switching regulator, this IC can be used for DC to DC voltage conversions such as buck, boost and inverting applications.
Construction and working
The DC motor is connected with DC power supply and output driver IRF 540 mosfet, the diode D1 provides protection from back emf, the mosfet gate terminal is driven by output signal from pin 5 of LM 3578, Pin 8, 7 and pin 6 are shorted together and connected with positive supply, components C1, C2 and R2 are connected between pin 1, 3 and ground supply, pin 2 of lm 3578 is connected with R1 and variable resistor VR1, by varying VR1 we can vary the speed of DC motor.
You can get datasheet of IC LM3578 here.
You can get datasheet of IRF 540 here.