The present disclosure relates generally to high-voltage startup circuits and the control methods thereof for power converters, and more particularly to high-voltage startup circuits that could have very low standby power consumption and high-speed transient response.
FIG. 1 demonstrates a conventional AC-to-DC power converter 10 with a flyback topology. Power controller 12, which is an integrated circuit for example, detects directly or indirectly output voltage VOUT at a secondary side to control power switch MN and regulate the power converted by the transformer with primary winding PRM, secondary winding SEC and auxiliary winding AUX.
Every power converter nowadays is required to consume as less power as possible when it stays at a no-load condition or a light-load condition. When load 14 in FIG. 1 is absent, meaning a no-load condition, power converter 10 consumes power majorly on four circuit portions including snubber 11, high-voltage startup circuit 18 inside power controller 12, the circuitry for continuously detecting output voltage VOUT, and power switch MN causing switching loss.
High-voltage startup circuit 18 is substantially in charge of boosting up operating voltage VCC while it is not high enough for the core circuits inside power controller 12 to function properly. Power controller 12 is for example a packaged integrated circuit with high-voltage pin HV, operating voltage pin VCC, driving pin GD and ground pin GND. When the core circuits inside power controller 12 cannot work normally due to an over-low operating voltage VCC, high-voltage startup circuit 18 sinks from high-voltage pin HV charging current ICHG to charge operating voltage capacitor C1 via operating voltage pin VCC, so as to boost up operating voltage VCC. When operating voltage VCC is high enough, high-voltage startup circuit 18 should stop charging current ICHG and consumes as low power as possible.