This dc motor speed controller is designed using pulse width modulation (PWM), and can be used in circuits for controlling electric motors speed that require a maximum current of 2A. Of course the circuit can also be used for engines that have a higher consumption of 2 A, except that in this case it is necessary to provide additional cooling to T2 transistor TIP3055 type, and increase the value of C2.
The circuit is based on IC1 IC type 40106. Output of IC1a remain in 0 state at a time determined by R1 and in state 1 a period determined by R2 and P1.
When the capacitor C1 is discharged the entry level of IC1a is bellow lower threshold, so its output is in state 1. Capacitor is charged quickly through D1 and R1 and reaches the top threshold in about 1,5ms, passing the IC1a output is state 0, condenser discharging through D2, R2 and P1.