Primary side turn-off of self-driven synchronous rectifiers
View Patent ↗There is disclosed a power conversion circuit including self synchronous rectifiers and a rapid shutdown section. When power is removed from the power conversion circuit, the rapid shutdown section prevents self oscillation of the self synchronous rectifiers. As a result, power is not drawn from the output and dissipated in the power conversion circuit.
1. A power conversion circuit comprising
a transformer having a primary side and a secondary side
an input section comprising four switches to drive a main winding of the primary side, said switches disposed as an upper pair and a lower pair
an output section connected to the secondary side and comprising a first synchronous rectifier and a second synchronous rectifier
a shutdown section comprising a control section and means for shorting the main winding of the primary side of the transformer, the shutdown section for reducing self-oscillation between the first synchronous rectifier and the second synchronous rectifier at a predetermined condition, wherein the control section is adapted to detect the predetermined condition
wherein the means for shorting the main winding 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.
2. The power conversion circuit of claim 1 wherein the shutdown section includes a DC blocking capacitor in series with the main winding of the primary side of the transformer.
3. 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.
4. A power converter comprising the power conversion circuit of any of claims 1 , 2 and 3 .
5. A method of operating a power converter including an input section, an output section comprising first and second self driven synchronous rectifiers, and a transformer comprising a primary side and a secondary side, the method comprising
shutting down said power converter in response to sensing a predetermined condition; and
reducing self-oscillation between the first synchronous rectifier and the second synchronous rectifier after shutting down said power converter
wherein the input section comprises four switches to drive a main winding of the primary side of the transformer, said switches disposed as an upper pair and a lower pair, and
the reducing step further comprises shorting the main winding of the primary side of the transformer by turning on a pair of switches selected from the group comprising the upper pair of switches and the lower pair of switches.
6. The method of operating a power converter of claim 5 further comprising
providing a control section and a shutdown section
the reducing step further comprising
the control section sensing said predetermined condition
the control section sending a signal to the shutdown section.
7. The method of operating a power converter of claim 5 wherein the predetermined condition comprises removal of external power from the input section.
8. The method of operating a power converter of claim 5 wherein the predetermined condition is selected from the group comprising falling below an undervoltage lockout point level, over-current and over-temperature.