A motor power controller can be constructed from 4 discrete power MOSFETs that are joined connected as shown in the diagram below:
The 4 power MOSFETs constitute a bridge. The control input switches on the transistors in pairs. Either Q1 or Q4 are on or Q2 and Q3 are on.This switches the current through the motor in just one direction or the other, functioning as a reversing switch.
This basic bridge circuit is in the central heart of many motor control ICs, but most have extra facilities. 4 protective diodes, 1 across each transistor, are a required addition. The Semi-conductors L6201 Full Bridge Driver contains circuits for detecting when the IC gets too hot and shuts it down. This could happen if the motor stalls because of mechanical overloading. The Logic circuits are installed for turning the output on and off. This can be done at high frequency with variable mark-space ratio so the driver controls speed and the direction as well. With these further features the IC is a good example of medium-scale integration & of the switch mode approach for circuit designing.
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