Self driven synchronous rectifier shutdown circuit and method
View Patent ↗There is disclosed a power conversion circuit comprising a transformer having a primary side driven by an input section and a secondary side connected to first and second self-driven synchronous rectifiers. A shutdown section includes a control section adapted to detect a predetermined condition and means for shorting a winding of the transformer upon detection of the predetermined condition.
1. A power conversion circuit comprising
a transformer having a primary side and a secondary side
an input section connected to the primary side
an output section connected to the secondary side and comprising a first self-driven synchronous rectifier and a second self-driven synchronous rectifier
a shutdown section comprising
a control section adapted to detect a predetermined condition
means for shorting a winding of the transformer upon detection of the predetermined condition, wherein shorting the winding on the transformer reduces self-oscillation between the first self-driven synchronous rectifier and the second self-driven synchronous rectifier.
2. The power conversion circuit of claim 1 wherein the shutdown section comprises means for shorting a main winding of the primary side of the transformer.
3. The power conversion circuit of claim 2 wherein
the input section comprises four switches to drive the main winding of the primary side of the transformer, said switches disposed as an upper pair and a lower pair
the shutdown section comprises means for turning on a pair of switches selected from the group comprising the upper pair of switches and the lower pair of switches.
4. The power conversion circuit of claim 3 wherein the shutdown section includes a DC blocking capacitor in series with the main winding of the primary side of the transformer.
5. The power conversion circuit of claim 1 wherein the shutdown section comprises means for shorting an auxiliary winding of the primary side of the transformer.
6. The power conversion circuit of claim 1 wherein the predetermined condition is selected from the group comprising falling below an undervoltage lockout point level, over-current, and over-temperature.
7. A power converter comprising the power conversion circuit of any of claims 1 - 6 .
8. A method of operating a power converter including a transformer comprising a primary side and a secondary side, an input section connected to the primary side, and an output section connected to the secondary side comprising first and second self-driven synchronous rectifiers, the method comprising
sensing a predetermined condition
shutting down said power converter in response to sensing the predetermined condition
shorting a winding on the transformer in response to sensing the predetermined condition, wherein shorting a winding on the transformer reduces self-oscillation between the first synchronous rectifier and the second synchronous rectifier after shutting down said power converter.
9. The method of operating a power converter of claim 8 wherein shorting a winding comprises shorting a main winding of the primary side of the transformer.
10. The method of operating a power converter of claim 9 wherein
the input section comprises four switches to drive the main winding of the primary side of the transformer, said switches disposed as an upper pair and a lower pair
shorting a winding further comprises turning on a pair of switches selected from the group comprising the upper pair of switches and the lower pair of switches.
11. The method of operating a power converter of claim 8 wherein shorting a winding comprises shorting an auxiliary winding of the primary side of the transformer.
12. The method of operating a power converter of claim 8 wherein the predetermined condition comprises removal of external power from the input section.
13. The method of operating a power converter of claim 8 wherein the predetermined condition is selected from the group comprising falling below an undervoltage lockout point level, over-current and over-temperature.