Reverse current control for an isolated power supply having synchronous rectifiers

1. A power supply, comprising:

a synchronous rectifier that rectifies an AC voltage to a DC voltage;

a reverse current control module configured to generate a signal when an input voltage is lower than a threshold, the reverse current control module including a transistor and a shunt regulator, wherein, when a voltage across a reference pin of the shunt regulator is lower than an internal reference voltage of the shunt regulator, a cathode of the shunt regulator is changed to a high resistance status, resulting in the turning off of the transistor; and

a control module that turns off the synchronous rectifier, after receiving the signal from the reverse current control module.

2. The power supply of claim 1 , further comprising:

an input power source that provides energy to a load, and

an input filter that decouples a ripple interference from the input power source.

3. The power supply of claim 1 , further comprising:

a switch located on a primary side to invert an input DC voltage into an AC voltage.

4. The power supply of claim 1 , further comprising:

a transformer that isolates an input and an output.

5. The power supply of claim 1 , further comprising:

an output filter that smooths a DC voltage rectified by the synchronous rectifier.

6. The power supply of claim 1 , wherein the reverse current control module senses an input voltage on a primary side and an output voltage on a secondary side.

7. The power supply of claim 1 , wherein the reverse current control module includes an input voltage detector, an output voltage detector, and a compare module configured to compare one or more voltages.

8. The power supply of claim 7 , wherein the input voltage detector includes

an input for an input voltage sensing and

an output coupled to the compare module.

9. The power supply of claim 7 , wherein the output voltage detector includes

an input for an output voltage sensing and

an output coupled to the compare module.

10. The power supply of claim 7 , wherein the compare module includes two inputs from the input voltage detector and the output voltage detector, and the compare module is configured to calculate a threshold based on an output voltage and at least one other parameter.

11. The power supply of claim 1 , wherein an input voltage detector senses a voltage on both a primary side and a secondary side that reflects the input voltage or that has relationship with the input voltage.

12. The power supply of claim 1 , further comprising:

a compare module configured to perform a compensation for both the input voltage and an output voltage to calculate a correct input and output voltage value.

13. The power supply of claim 1 , further comprising:

a compare module that calculates a voltage threshold dynamically or sets the threshold as a predetermined value.

14. The power supply of claim 1 , further comprising:

a first block that decouples noise, and

a second block that attains a certain delay time, wherein at least some portions of the power supply maintain an input signal and an output signal for a predetermined time.

15. The power supply of claim 1 , wherein the control module is configured to disable one or more driving signals for the synchronous rectifier.

16. The power supply of claim 1 , wherein the reverse current control module and the control module are implemented as an analog circuit, a digital circuit, a hybrid circuit, or software executed in a memory or in conjunction with a processor.

17. The power supply of claim 1 , further comprising:

a compare module that senses the input voltage on a primary side.

18. The apparatus of claim 1 , wherein, when the voltage across the reference pin of the shunt regulator is higher than the internal reference voltage of the shunt regulator, the cathode of the shunt regulator leads to a saturation of the transistor.

19. A method, comprising:

sending a first signal from a reverse current control module to a control module when an input voltage is lower than a threshold, the reverse current control module including a transistor and a shunt regulator, wherein, when a voltage across a reference pin of the shunt regulator is lower than an internal reference voltage of the shunt regulator, a cathode of the shunt regulator is changed to a high resistance status, resulting in the turning off of the transistor; and

sending a second signal from the control module to turn off a synchronous rectifier, in response to the first signal.

20. The method of claim 19 , wherein the first signal is sent when an input voltage dips.

21. The method of claim 19 , further comprising:

sensing the input voltage on a primary side and an output voltage on a secondary side; and

calculating the threshold based on at least the output voltage.

22. The method of claim 19 , further comprising:

compensating a voltage plateau to achieve a value for the input voltage.

23. A method implemented by a power supply, the method comprising:

rectifying, with a synchronous rectifier, an AC voltage to a DC voltage;

generating, with a reverse current control module, a signal when an input voltage is lower than a threshold, the reverse current control module including a transistor and a shunt regulator, wherein, when a voltage across a reference pin of the shunt regulator is lower than an internal reference voltage of the shunt regulator, a cathode of the shunt regulator is changed to a high resistance status, resulting in the turning off of the transistor; and

turning off the synchronous rectifier, with a control module, after the control module receives the signal from the reverse current control module.

24. The method of claim 23 , further comprising:

sensing the input voltage on a primary side and an output voltage on a secondary side; and

calculating the threshold based on at least the output voltage.