Controlling the sense of rotation with a H-bridge
The circuit below shows the power unit to control the direction of rotation of a DC motor. In this so-called H-bridge transistors serve as electronic switches. In power electronics, MOSFETs or IGBTs are often used to switch large currents.
Which transistors have to be switched on for motor clockwise (UA> 0) and motor counterclockwise (UA <0) rotation?
What tasks have the diodes have in this H-bridge?
CR: V1 and V7 CCR: V5 and V3
These diodes serve as freewheeling diodes to protect against voltage peaks, which occur when inductive loads are switched off.
Controlling the speed of rotation
The pulse diagram of the applied armature voltage illustrates the principle of pulse width modulation PWM. The course of the motor or armature voltage is recorded by an oscilloscope. The following picture of the armature voltage shows how low and high speed can be achieved:
Parameters which describe this rectangular signal:
- f = 1 / T f frequency, T period duration
- Duty cycle = ti / T
Combining the principle of pulse width modulation with the H-bridge, speed and sense of rotation can be controlled continuously:
MOS-FET = Metal–Oxide–Semiconductor Field-Effect Transistor
IGBT = Insulated Gate Bipolar Transistor
PWM `= Pulse Width Modulation