Complete H-Bridge (MEC129E)

This article was taken from my book Robotics, Mechatronics and Artificial Intelligence (sold out) published in the United States and also from previous articles in other publications, with minor updates. It shows a complete H-bridge using Bipolar and MOSFET transistor. It is ideal for controlling DC motors and can be used as a shield.

This circuit (Figure 1) combines power MOSFETs with common bipolar NPN transistors and operates with two inputs. 

A feedback circuit provides protection against the forbidden states. When this state is forced by the inputs, the feedback to the base of Q3 and Q4 does not allow them to be conductive at the same time.


Figure 1     Complete H-bridge.
Figure 1 Complete H-bridge.


The Power MOSFETs can be chosen according to the motor using the tables in Section 4.5, Additional Information. The bipolar transistors are BC548 or any other general-purpose NPN silicon transistor.

The two LEDs act as direction indicators. The value of resistor R3 depends on the voltage used to power the circuit according to the following table:




The control voltage can be supplied by common TTL or CMOS gates or operational amplifiers.

The circuit can be used as an efficient control shield for microcontrollers. Remember that power transistors must be mounted on good heat sinks.

    Eventually resources to avoid motor switching noise should be added in parallel with it.