The present invention relates to electrical rectification circuits, and in particular, to synchronous rectifiers which are controlled rectification devices. More particularly, the present invention relates to an integrated synchronous rectifier which can be substituted for a non-synchronous rectifier in a rectification circuit with minimal circuit change.
Output rectification in off-line isolated power supplies is often implemented by use of Schottky or PIN diodes. The typical disadvantage is that every diode has a nominal threshold voltage and therefore high conduction losses. Synchronous rectification has been introduced for flyback converters and in other applications where a MOSFET or other controlled switch is driven by an appropriate drive circuit to emulate the operation of a diode. The disadvantage of the MOSFET synchronous rectifier is the added complexity in the design of the rectification stage, which in the case of normal diode rectification, is very simple, consisting of only a diode. In particular, to substitute a synchronous rectifier for a diode requires the addition of the drive circuitry for the synchronous rectification device, leading to increased complexity and a larger number of circuit components.
Applicant is aware of the following prior art:
U.S. Pat. No. 6,353,544 uses a current transformer to sense current, making it impracticable for an integrated solution. U.S. Pat. No. 6,442,048 is another prior art example, which cannot be used to provide a one package integrated solution with a minimal external terminal count.