DC motor pulse width speed regulation circuit

Circuit working principle: Although the most commonly used speed control method is pulse width modulation ,
this circuit uses pulse position modulation (also known as pulse time modulation). The integrated block 555 is connected here to form a
square wave modulator, and the pulse width of its pin 3 output is fixed 0.5 ms (
determined by the time constants of R. and C.). Therefore, the
motor is switched on via VT for 0.5 ms for each pulse duration . This time is sufficient for most electric motors to start.