Synchronous rectifier

Patent metadata

Field	Value
Publication number	US-9923475-B2
Application number	US-201615142615-A
Country	US
Kind code	B2
Filing date	Apr 29, 2016
Priority date	Apr 29, 2016
Publication date	Mar 20, 2018
Grant date	Mar 20, 2018

Abstract

Disclosed is a method to control the synchronous rectification in a power converter including a primary winding and a secondary winding, including detecting a peak current in a secondary winding, determining a blanking threshold based on the peak current, and blanking a turning off of a synchronous rectifier (SR) switch for a blanking time based on the blanking threshold.

First claim

The invention claimed is:

1. A method to control the synchronous rectification in a power converter including a primary winding and a secondary winding, comprising:
detecting a peak current in a secondary winding;
determining a blanking threshold based on the peak current; and
blanking a turning off of a synchronous rectifier (SR) switch for a blanking time based on the blanking threshold;
wherein determining the blanking threshold comprises:
sensing a drain to source voltage of a switch connected in series with the secondary winding;
charging the gate voltage of the SR switch until the sensed drain to source voltage reaches a predetermined regulation level.

2. The method of claim 1 , wherein the gate voltage has a monotonic relation with the peak current when the drain to source voltage is regulated to a constant level.

3. The method of claim 1 , wherein the peak current related signal is obtained by measuring the gate voltage with a constant and regulated drain to source voltage.

4. The method of claim 1 , wherein the blanking time is a function of the peak current and where the blanking time gradually increases with the peak current.

5. The method of claim 1 , wherein the blanking time is zero for low peak currents.

6. The control method of claim 5 , where the zero blanking time is applied for a SR gate voltage just above the threshold of a logic level FET in low voltage applications and for a SR gate voltage just above the threshold of a standard level FET in high voltage applications.

7. The method of claim 1 , wherein the blanking time is zero for SR switch turn-on by low frequency ringing between the end of a secondary stroke and the beginning of a next primary stroke.

8. The method of claim 1 , wherein blanking the turning off of the SR switch comprises:
charging the capacitor; and
outputting a blanking signal for an increasing duration based on the charging level of the capacitor.

9. The method of claim 8 , comprising stopping the blanking signal when a capacitor voltage equals the regulated gate voltage.

10. The method of claim 1 , wherein a blanking signal is turned off when the blanking time corresponds to the blanking threshold.

11. A power converter, comprising:
a secondary current winding configured to receive a peak current;
a synchronous rectifier (SR) switch configured to rectify current in the secondary winding, the SR switch having a source, drain and gate;
an SR controller to control the SR switch, the SR controller comprising:
a peak current detector configured to produce an output signal related to the peak current value of a secondary current; and
a blanking circuit configured to set a blanking time based upon the output gate signal related to the peak current value
wherein the peak current is obtained by measuring a drain to source voltage of the SR switch with the SR gate charged such that a defined VDS voltage is reached.

12. The power converter of claim 11 , wherein the blanking time is a function of the peak current and where the blanking time gradually increases with the peak current.

13. A power converter, comprising:
a secondary winding having a peak current;
a synchronous rectifier (SR) switch to rectify current in the secondary winding;
an SR controller to control the SR switch, the SR controller comprising:
a detecting circuit to detect a peak current in the secondary winding;
regulation circuitry to determine a blanking time based on the peak current; and
a blanking circuit to blank the SR switch for the blanking time;
wherein blanking the SR switch comprises: charging a capacitor; and

outputting a blanking signal for an increasing duration based on the charging level of the capacitor.

14. The converter of claim 13 , wherein the blanking circuit comprises:
a current source to power a current loop, the current loop including a resistor and the capacitor;
a comparator block to compare a charge level of the capacitor to the gate voltage.

15. The converter of claim 14 , wherein the blanking time is defined by a value of the resistor multiplied by a value of the capacitor.

16. The converter of claim 13 , wherein the blanking time is independent of a converter output voltage and controller supply voltage.

17. The converter of claim 13 , wherein the blanking circuit comprises:
an input to represent a representation of the peak current of the SR switch; and
a latching component to output a blanking signal that prevents ringing in the current of the secondary winding from interfering with gate switching of the SR switch.

18. A power converter, comprising:
a secondary winding having a peak current;
a synchronous rectifier (SR) switch to rectify current in the secondary winding;
an SR controller to control the SR switch, the SR controller comprising:
a detecting circuit to detect a peak current in the secondary winding;
regulation circuitry to determine a blanking time based on the peak current; and
a blanking circuit to blank the SR switch for the blanking time;
wherein the blanking circuit comprises:
an input to represent a representation of the peak current of the SR switch; and
a latching component to output a blanking signal that prevents ringing in the current of the secondary winding from interfering with gate switching of the SR switch.

Assignees

• Nxp Bv

Inventors

• Kleinpenning Jeroen
• Dikken Jan

Classifications

• H02M7/2173 Primary

  in a biphase or polyphase circuit arrangement (H02M7/2176 takes precedence; voltage multipliers H02M7/25) · CPC title

• H02M3/33592 Primary

  having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer · CPC title

• H02M5/10

  using transformers · CPC title

• H02M1/08

  Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters · CPC title

• H02M2001/0009

  Electricity · mapped topic