Patent ID: 8218339

Claim:
A power converter comprising: a switching circuit for receiving an input voltage; a transformer having a primary winding and a secondary winding, wherein the primary winding is connected to a power output terminal of the switching circuit; a main control circuit connected to a control terminal of the switching circuit for outputting a main control signal and thereby manipulating the switching circuit and allowing the energy of the input voltage to be transferred to the primary winding through the switching circuit; at least one synchronous rectifier connected in series with the secondary winding and a second common node; at least one current transformer connected in series with the a synchronous rectifier for outputting a detecting signal according to a current flowing through the synchronous rectifier; and at least one synchronous rectification control circuit connected to a control terminal of the synchronous rectifier, the current transformer, and a control terminal of the switching circuit for receiving the detecting signal and the main control signal and outputting a synchronous rectification control signal to manipulate the synchronous rectifier; wherein the synchronous rectification control circuit further includes a comparator circuit having a general comparing resistor and a comparator unit, wherein a first end of the general comparing resistor is connected to the current transformer for receiving the detecting signal and a second end of the general comparing resistor is connected to an input terminal of the comparator unit, and wherein an output terminal of the comparator unit is connected to a control terminal of the synchronous rectifier, and wherein the comparator circuit is configured to change a level of the synchronous rectification control signal to a disable level when the detecting signal is higher than a reference voltage, thereby manipulating the synchronous rectifier to turn off.