An H-bridge is an electronic circuit that reverses the voltage/current across a connected load or output terminal. These circuits can be used in robots and other practical applications for forward/reverse control and speed control of DC motors, stepper motor control (bipolar stepper motors must also include motor controllers with two H-bridges), most DC-AC converters (such as inverters and frequency converters), some DC-DC converters (push-pull converters), and other power electronic devices.
The H-bridge is a typical DC motor control circuit. It gets its name from its circuit shape, which resembles the letter H. Four transistors form the four vertical legs of the H, while the motor is the horizontal bar of the H.
H-bridge circuits can be built using discrete components or integrated onto an integrated circuit. The name "H-bridge" comes from its circuitry, which consists of two parallel branches and a load input/output branch, forming a circuit structure resembling the letter "H".
As shown in the diagram above, the working principle of a single-phase bridge inverter circuit is as follows: When switches T1 and T4 are closed and T2 and T3 are open: u0 = Ud; when switches T1 and T4 are open and T2 and T3 are closed: u0 = -Ud; when switches T1, T4 and T2, T3 are alternately switched at a frequency fS, an alternating voltage waveform (alternating positive and negative square waves) is obtained across the load resistor R, with a period Ts = 1/fS. This converts the DC voltage E into an AC voltage uo. uo contains harmonics; to obtain a sinusoidal voltage, it can be filtered using a filter.
The main circuit switches T1~T4 are actually idealized models of various semiconductor switching devices. Commonly used switching devices in inverter circuits include fast thyristors, gate turn-off thyristors (GTOs), power transistors (GTRs), power MOSFETs, and insulated-gate transistors (IGBTs).
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