by Ramsey Electronics
This useful kit uses a technique known as Pulse Width Modulation (PWM) to control the speed of DC motors. It runs on 6-15 VDC and is able to control any DC motor from 3-50 volts at up to 10 Amperes.
Pulse Width Modulation controls speed without lowering torque -- the DC motor receives full voltage whenever energized and only the duration of the voltage pulse changes. The motor will rotate smoothly and with full power -- no matter what the speed.
At the heart of the circuit are two 555 industry standard ICs. The first oscillates at a 400Hz rate generating the clock frequency, the other is configured as a pulse width modulator. By changing the control voltage on pin 5, the duty cycle of the output can be controlled. The pulse width modulated output is then fed to the gate of a high current MOSFET transistor which does the actual controlling of the motor. A separate power supply can be used to run the motor independently of the controller power supply, as long as the power supply grounds are tied together.