Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Patent
1994-12-08
1997-06-03
Sterrett, Jeffrey L.
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
363127, H02M 7217
Patent
active
056361165
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to rectifier circuits and, more particularly, to a synchronous rectifier circuit that is impervious to reverse feed.
2. History of the Related Art
Feeder devices with synchronous rectifiers are known per se, and are in use as electric power supplies. In the same way, such devices are known from publications, for example, from O. Kilgenstein, Schaltnetzteile in der Praxis, Wuerzburg, 1992. Each of the known devices has a range of operation that is limited at the top by the maximum output current at which the output voltage is still regulated to the desired value.
If, either temporarily or for long periods, the current requirement is greater than the capacity of a single device and the selection of a similar device of greater capacity is not indicated for certain reasons, then these devices are connected in parallel.
If in one of the devices that is connected together in parallel in this manner, an operating state arises in which either the output voltage drops or the oscillator no longer triggers or interrupts the primary transformer, then the devices that are connected in parallel with the device under consideration feed power back into the device that is either temporarily or permanently out of service, which as a rule leads to the destruction of the controlled rectifier or to a collapse of the output voltage.
The present invention provides an improvement over the prior art by providing a synchronous rectifier circuit that is impervious to reverse feed, and that is fully capable of operation in all operating states.
SUMMARY OF THE INVENTION
The present invention relates to a synchronous rectifier circuit which includes a direct-current source whose flow of current through the primary winding of a transformer is periodically switched on and off by means of an electronic switch. The circuit contains, as a controlled rectifier, a first and second MOSFET. If two or more such synchronous rectifiers are connected together in parallel, in the event of the failure of a synchronous rectifier, the first and second MOSFETS are protected from destruction resulting from reverse feed from the failed rectifier or the remaining rectifier by the present invention.
More particularly, one aspect of the present invention includes the insertion of a third and a fourth MOSFET into the circuit which includes a first capacitor connected across the output thereof. The source terminal of the third MOSFET is connected to the gate terminal of the first MOSFET and the source terminal of the fourth MOSFET is connected to the gate terminal of the second MOSFET. Each source terminal of the third and fourth MOSFETS is connected to one output of the circuit through a separate resistor. Each gate terminal of the third and fourth MOSFETS is connected to one end of the secondary winding through a resistor and to the one output through a second capacitor. The other output of the circuit is connected to one end of the secondary winding of the transformer through a choke. The other end of the secondary winding is connected to the drain terminal of the second MOSFET. A Schottky diode is connected across the drain and source terminals of the first MOSFET. A switching block is connected between the one output and the source terminal of the first MOSFET to measure the current flowing through the first MOSFET and the Schottky diode. The output of the switching block is input to a logic unit whose output is connected across the second capacitor. If the induction voltage through the secondary winding of the transformer is too small, then the first and second MOSFETS block and the logic unit short circuits the second capacitor and ensures a clean change from the type of operation with connected rectifiers to non-sensitive diode operation.
In another aspect, the present invention relates to the circuit described above wherein the switching block includes a transformer whose primary winding is connected in series with the parallel connection of the first MOSFET and th
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patent: 5430640 (1995-07-01), Lee
Blanc; "Practical Application of MOSFET Synchronous Rectifiers"; Nov. 1991; IEEE Intelec 91, pp. 495-501.
Allington Philip
Milavec Johann
Melcher AG
Sterrett Jeffrey L.
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