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
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.