Bootstrap refresh control circuit, power converter and associated method

A power converter, comprising:

• an input port configured to receive an input voltage;
• an output port configured to provide an output voltage and an output current;
• a high side switch and a low side switch coupled in series between the input port and a reference ground, wherein the high side switch and the low side switch has a common connection forming a switching output terminal, providing a switching voltage;
• an output filter coupled between the switching output terminal and the output port to convert the switching voltage into the smoothed output voltage;
• a bootstrap circuit comprising a bootstrap capacitor coupled to the input port and the low side switch, wherein the bootstrap circuit is configured to charge the bootstrap capacitor to provide a bootstrap voltage there across when the low side switch is turned on;
• and
• a bootstrap refresh control circuit having a bootstrap input terminal configured to receive the bootstrap voltage, and an output control terminal configured to provide an enhanced high side driving signal to the high side switch for driving the high side switch to switch on and off periodically;
• wherein the bootstrap refresh control circuit is further configured to control the charging of the bootstrap capacitor through regulating the on and off switching of the high side switch and the low side switch based on the bootstrap voltage;
• and wherein the bootstrap refresh control circuit is further configured to regulate the high side switch and the low side switch to switch on and off in complementary with a substantially constant frequency when the bootstrap voltage is lower than a first threshold signal
• further wherein the bootstrap refresh control circuit comprises:
• a first comparison module having a first comparing input terminal, a second comparing input terminal and a first comparing output terminal, wherein the first comparing input terminal is configured to receive the bootstrap voltage, the second comparing input terminal is configured to receive the first threshold signal, and the first comparison module is configured to compare the bootstrap voltage with the first threshold signal to provide a bootstrap refresh signal at the first comparing output terminal;
• and
• a control module having a first control input terminal configured to receive the bootstrap refresh signal, wherein the control module is configured to regulate the on and off switching of the high side switch and the low side switch at least partially based on the bootstrap refresh signal so as to control charging of the bootstrap capacitor.

A method for controlling 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 power converter is configured to receive an input voltage and to provide an output voltage and an output current based on driving the high side switch and the low side switch to switch on and off, the method comprising:

• sensing the bootstrap voltage across the bootstrap capacitor;
• comparing the bootstrap voltage with a first threshold signal to provide a bootstrap refresh signal based on the comparison of the bootstrap voltage and the first threshold signal;
• and
• regulating the on and off switching of the high side switch and the low side switch based at least partially on the bootstrap refresh signal in order to control charging of the bootstrap capacitor to refresh the bootstrap voltage;
• wherein regulating the on and off switching of the high side switch and the low side switch comprises regulating the high side switch and the low side switch to switch on and off in complementary with the substantially constant frequency when the bootstrap voltage is lower than the first threshold signal
• further wherein
• the bootstrap refresh signal has a first logic state when the bootstrap voltage is lower than the first threshold signal and has a second logic state when the bootstrap voltage is higher than the first threshold signal;
• and wherein
• if the bootstrap refresh signal is at the first logic state, regulating the high side switch and the low side switch to switch on and off in complementary with a substantially constant frequency, if the bootstrap refresh signal is at the second logic state, regulating the high side switch and the low side switch to switch on and off according to the output voltage and the output current.