Patent ID: 8278900

Claim:
A power supply, comprising: a power factor correction stage having power inputs for receiving input power and power outputs for outputting output power at a power factor output stage voltage; wherein the power factor correction stage can be switched between an operating mode and an off mode; a switched mode power stage having output terminals for supplying output power to a load at a supply voltage and input terminals connected to the power outputs of the power factor correction stage for receiving power at the power factor output stage voltage; wherein the power supply is arranged to be switchable between a normal mode and a standby mode; the power supply further comprising a controller for controlling the power factor correction stage to supply in the normal mode a normal power factor output stage voltage to the switched mode power stage and to operate in the standby mode in a burst mode to supply power in a voltage range below the normal power factor output stage voltage; wherein the controller is arranged in the standby mode to switch on the power factor correction stage for a burst when the power factor output stage voltage falls below a low burst level and to switch off the power factor correction stage to end the burst when the power factor output stage voltage rises above a high burst level higher than the low burst level, the high and low burst levels both being below the normal power factor output stage voltage; wherein the controller includes: a bistable device having an output connected to the power factor correction stage to control whether the power factor connection stage is in a burst mode or not; a first comparator for comparing the power factor output stage voltage with the low burst level, the first comparator being connected to the bistable device to switch the bistable device to the burst mode when the power factor output stage voltage falls below the low burst level; and a second comparator for comparing the power factor output stage voltage with the high burst level, the second comparator being connected to the bistable device to switch the bistable device out of the burst mode when the power factor output stage voltage rises above the high burst level; and an OR gate having as a first input, the output from the bistable device and having as a second input, a signal on a normal mode operating line that is connected to a control output of the switched mode power stage, wherein the OR gate causes the power factor correction stage to operate either when the normal operation signal is applied on the normal mode operating line or after the power factor output stage voltage falls below the low burst level or until the power factor output stage rises above the high burst level.