What is the bootstrap circuit in high-voltage IPDs?

A bootstrap circuit is used for the gate drive of the high-side (upper-leg) devices of a bridge circuit.

Fig. 1 Example of a bootstrap circuit
Fig. 1 Example of a bootstrap circuit

Generally, the gate of N-channel MOSFETs or IGBTs is driven at a voltage 10 to 15 V higher than the source voltage or emitter voltage. When a high-side device turns on, the source (or emitter) voltage becomes equal to that of the high-voltage power supply (VBB). Therefore, a power supply with very high voltage, which is equal to the sum of VBB and the gate-source (gate-emitter) voltage, is required for the gate drive of the high-side device. The following shows a bootstrap circuit. When the low-side device turns on, the bootstrap capacitor (C) stores charge, which is used to drive the gate of the high-side device.

Fig. 2 work of Bootstrap(1)
Fig. 2 work of Bootstrap(1)
Fig. 3 work of Bootstrap(2)
Fig. 3 work of Bootstrap(2)

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