DC-motor with brushes: Change the rotation direction left and right

 

To control the position or speed of the DC-motor you have to change the current respectively the supply voltage of the DC-motor.

If you change the DC-voltage polarity than you change the rotation direction. If you have an application like a pump, that rotate only in one direction, so you need only one switch for on/off of the supply voltage. If you want to change the speed or torque, so you have to control the current of the DC-motor. Normally you switch the DC-supply voltage with a PWM (Pulse With Modulation) on and off (frequency up to 20kHz) and therefore you can control the current of the DC-motor.

 

If additionally you want to change the rotation direction, so you need at the end 4 switches that are connected together like a H (H-bridge).

Only two of this 4 switches are connected and modulated with PWM.

If you switch ON the both lower switches, than you get better braking of the motor.