What is the function of the flyback diode in the H-bridge circuit?

What is the function of the flyback diode in the H-bridge circuit?

In general, the "fly diode" in a circuit is used to protect components from being punctured or burned out by induced voltage.

In an H-bridge circuit, it is connected parallel with each MOSFET switch, across the two ends of the inductor (load).

So, what is its role in the H-bridge circuit?

(1) Prevent sudden changes in current

When the power switch in the circuit is switched, according to Lenz's law, the motor winding will a reverse electromotive force to maintain the original current direction.

When Q1 and Q4 are turned off, the reverse electromotive force generated by the winding will cause a tendency for the current to continue to flow in the direction of Q1 and Q4. At this time, the two flyback diodes D2 D3 will conduct.

D2 and D3 provide a path for the current in the motor winding to continue flowing, avoiding a sudden change in current. Without two flyback diodes, the reverse electromotive force generated by the motor winding may produce extremely high voltage spikes at the two ends of Q1 and Q4 causing Q1 and Q4 to be punctured and damaged.

(2) Provide a path

During the operation cycle of the H-bridge circuit, when diagonal switches are turned on or off simultaneously, for example, Q1 and Q4 are turned on at the same time (the motor rotates forward), the flows from the power supply Vbat through Q1, the motor M, and Q4 to form a loop.

When Q1 and Q4 are turned off, the current in the motor winding needs a path to maintain continuity. At this time, D2 and D3 conduct, providing a path for the current.

 path is essential for maintaining the continuity of the current in the inductor (motor winding), especially in applications where a smooth DC voltage needs to be output.

 summary, the flyback diode in the H-bridge circuit prevents sudden changes in current, provides a path, and ensures that the current in the inductor changes, thereby achieving effective power control and motor drive.