Discharge process of bootstrap circuit

As shown in the figure, this is the equivalent circuit when the switch is turned off (triode is turned off). When the switch is turned off (the triode is turned off), the current flowing through the inductor will not immediately become 0, but will gradually become 0 from the value at the end of charging due to the current holding characteristics of the inductor. The original circuit has been disconnected, and the inductor can only be discharged through the new circuit, that is, the inductor begins to charge the capacitor, and the voltage across the capacitor rises, and the voltage is already higher than the input voltage. Booster complete.

Speaking of it, the boosting process is the energy transfer process of an inductor. Inductor absorbs energy when charging and releases energy when discharging. If the capacitance is large enough, a continuous current can be maintained at the output when discharging. If this switching process is repeated, a voltage higher than the input voltage can be obtained on the capacitor.

P-channel high-side gate driver

Direct drive: suitable for maximum input voltage less than gate-source breakdown voltage of devices.

Open collector: The method is simple, but it is not suitable for directly driving MOSFET in high-speed circuit.

Level shift driver: suitable for high-speed applications and can be seamlessly matched with ordinary PWM controller.

N-channel high-side gate driver

Direct drive: The simplest high-end application of MOSFET is directly driven by PWM controller or ground driver, but the following two conditions must be met:

VCC<Vgs, max and Vdc< miller ·VCC-Vgs

Floating grid drive: the cost impact of independent power supply is very significant; Optocouplers are relatively expensive, have limited bandwidth and are sensitive to noise.

Transformer coupling driver: completely control the power grid in uncertain period; But it limits the switching performance to some extent. But this can be improved, but the circuit is more complicated.

Charge pump driver: for switching applications, the conduction time is often very long; Due to the inefficiency of the voltage multiplier circuit, more low-pressure pumps may be needed.

Bootstrap driver: simple, cheap and limited; For example, the duty cycle and on-time are limited by refreshing the bootstrap capacitor. The need of level conversion and related problems.