Abstract: A power supply system (10) forms an active zone that facilitates the power supply system (10) enabling an output transistor (37) when the input voltage (30) is between a first voltage value and a second voltage value. When the output transistor is enabled, it forms a load current (35) having an instantaneous value that when averaged over the period of the input signal results in a desired average value of the load current.

Abstract: A synchronous rectifier circuit (10) includes a polarity comparator (14) that generates a signal to a driver circuit (16) for controlling the voltage at the gate of a power MOSFET (60). The power MOSFET (60) is switched to operate in the conduction mode and short out a parasitic diode (62) when the diode is forward biased. The power MOSFET (60) is switched to operate in the nonconduction mode when the parasitic diode (62) is reverse biased. A bias supply circuit (12) uses a capacitor (70) to generate a regulated internal bias that provides power to the polarity comparator (14) and to the driver circuit (16). The internal bias allows the power MOSFET (60) to provide a current conduction that is substantially isolated from the changes in voltage levels at the terminals (64, 66) of the synchronous rectifier circuit (10).