Patent ID: 9577520
Date: 2017-02-21
CPC Classifications: H02M,Y02B

Claim:
1. A bootstrap circuit for a power converter, wherein the power converter comprises a high side switch, a low side switch and a bootstrap capacitor for providing a bootstrap voltage to supply a high side driver of the high side switch, and wherein the bootstrap capacitor has a first terminal and a second terminal, and wherein the power converter is configured to receive an input voltage and to provide an output voltage by means of turning the high side switch and the low side switch on and off, the bootstrap circuit comprising: a first charging circuit having an input terminal and an output terminal, wherein the input terminal is configured to receive the input voltage, and wherein the output terminal is coupled to the first terminal of the bootstrap capacitor; a first comparing circuit having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is configured to receive the input voltage, and wherein the second input terminal is configured to receive the output voltage, and further wherein based on a first threshold voltage and a voltage difference between the input voltage and the output voltage, the first comparing circuit is configured to provide a comparing signal at the output terminal; a boost circuit having an input terminal and an output terminal, wherein the input terminal is configured to receive the input voltage or the output voltage, and wherein the output terminal is configured to provide a first high voltage; and a second charging circuit having an input terminal, a control terminal and an output terminal, wherein the input terminal is configured to receive the first high voltage, and wherein the output terminal is coupled to the first terminal of the bootstrap capacitor, and wherein the control terminal is configured to receive the comparing signal, and wherein the second charging circuit is configured to charge the bootstrap capacitor when the voltage difference between the input voltage and the output voltage is smaller than the voltage threshold.