Energy conversion architecture with secondary side control delivered across transformer element

• US 9,118,253 B2
• Filed: 04/17/2013
• Issued: 08/25/2015
• Est. Priority Date: 08/15/2012
• Status: Active Grant

• Current Assignee: Flextronics America LLC (Flextronics International Limited)
• Original Assignee: Flextronics America LLC (Flextronics International Limited)
• Inventors: Telefus, Mark
• Primary Examiner(s): Dole, Timothy J
• Assistant Examiner(s): AHMED, YUSEF A
• Application Number:
  US13/865,022
• Publication Number:
  US 20140204619A1
• Time in Patent Office: 860 Days
• Field of Search: 363 16- 19, 363 2101- 2118, 363/34, 363/44, 363/84, 363/89, 363 97- 98, 363125-127
• US Class Current: 1/1
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop
• CPC Class Codes: H02M 3/33576 having at least one active switching element at the secondary side of an isolation transformer

Abstract

A switched mode power converter is configured having predominate secondary side control. A primary side driving circuit is configured as a responsive state machine the output of which is input as the driving signal for a main switch. An output voltage, current or power is sensed and the secondary side controller compares the sensed output characteristic with a predefined reference. The comparison results in an error that signifies an amount that the output is out of regulation. The secondary side controller drives a secondary side switch to generate a voltage pulse across the secondary winding. The voltage pulse has a pulse width that represents the amount of error in the output characteristic. The voltage pulse is transmitted across the transformer and received by the primary side driving circuit, which generates a driving signal modulated according to the voltage pulse and drives the main switch to regulate the output characteristic.

Claims

1. A method of controlling a switching mode power converter comprising:

a. configuring a switching mode power converter comprising a transformer, an output circuit coupled to a secondary winding of the transformer, a first switch coupled to a primary winding of the transformer and a state machine coupled to the first switch, wherein the output circuit comprises a second switch coupled to the secondary winding of the transformer and a controller coupled to the second switch;

b. measuring an output characteristic of the output circuit;

c. generating a second switch driving signal by the controller and applying the second switch driving signal to the second switch, wherein the second switch driving signal is modulated based on the measured output characteristic, and applying the second switch driving signal to the second switch results in a first voltage pulse across the secondary winding, the first voltage pulse comprising a pulse width that corresponds to a magnitude of an out of regulation output characteristic;

d. transmitting the first voltage pulse through the transformer and inputting a second voltage pulse proportional to the first voltage pulse across the secondary winding to the state machine;

e. generating a first switch driving signal by the state machine, wherein the first switch driving signal is modulated according to the pulse width; and

g. driving the first switch using the first switch driving signal to regulate the output characteristic.

2. The method of claim 1 further comprising determining for each switching cycle of the power converter when a power delivery from a primary side of the transformer to the output circuit is completed, and when the power delivery is completed then generating the driving signal and transmitting the first voltage pulse.

3. The method of claim 2 wherein the power delivery is completed when a current through the secondary winding drops to zero.

4. The method of claim 2 wherein the power delivery from the primary side to the output circuit corresponds to the first switch being OFF, and generating the second switch driving signal and transmitting the first voltage pulse are performed while the first switch is OFF.

5. The method of claim 1 wherein the state machine is a pulse width modulation circuit and the first switch driving signal comprises a pulse width modulated voltage signal.

6. The method of claim 5 wherein the second voltage pulse received by the pulse width modulation circuit modulates a duty cycle of the pulse width modulated voltage signal output from the pulse width modulation circuit.

7. The method of claim 1 wherein the output characteristic is one or more of an output voltage, an output current, and an output power of the power converter.

8. The method of claim 1 wherein the first voltage pulse is formed across the secondary winding while the second switch is ON which enables a negative secondary current through the secondary winding.

9. The method of claim 8 wherein enabling the negative secondary current comprises enabling an alternative current path from an output capacitor in the output circuit to the secondary winding.

10. The method of claim 1 wherein the secondary winding is magnetically coupled to an auxiliary winding, and the auxiliary winding is coupled to the state machine, further wherein transmitting the first voltage pulse comprises using the magnetic coupling between the secondary winding and the auxiliary winding to transmit the first voltage pulse from the secondary winding through the transformer such that the second voltage pulse is input to the state machine.

11. The method of claim 1 wherein transmitting the first voltage pulse comprises using a parasitic capacitance between a primary side and a secondary side of the power converter.

12. The method of claim 11 wherein the parasitic capacitance comprises a parasitic capacitance of the transformer.

13. The method of claim 11 wherein the parasitic capacitance comprises an inherent capacitance of a printed circuit board onto which the power converter is assembled, wherein the inherent capacitance is a result of a component layout on either side of an isolation galvanic barrier.

14. The method of claim 1 wherein the first switch comprises a first transistor and the second switch comprises a second transistor.

15. A switching mode power converter comprising:

a. a transformer having a primary winding coupled to an input supply voltage and a secondary winding;

b. a first switch coupled in series to the primary winding;

c. a state machine coupled to the first switch, wherein the state machine is configured to output a first switch driving signal to drive the first switch ON and OFF;

d. a second switch coupled in series to the secondary winding;

e. a controller coupled to the second switch, wherein the second controller is configured to turn the second switch ON and OFF;

f. a sensing circuit coupled to the secondary winding and the controller, wherein the sensing circuit is configured to sense an output characteristic of the power converter,

wherein the controller is configured to generate a second switch driving signal and apply the second switch driving signal to the second switch, wherein the second switch driving signal is modulated based on the measured output characteristic, and applying the second switch driving signal to the second switch results in a first voltage pulse across the secondary winding, the first voltage pulse comprising a pulse width that corresponds to a magnitude of an out of regulation output characteristic, further wherein the transformer is configured as a signal transmitter to transmit the first voltage pulse from the secondary winding to a primary side of the transformer, wherein the state machine is configured to input a second voltage pulse proportional to the first voltage pulse across the secondary winding and to generate the first switch driving signal modulated according to the pulse width.

16. The power converter of claim 15 wherein the controller and the sensing circuit are configured to determine for each switching cycle of the power converter when a power delivery from a primary side of the transformer to the output circuit is completed, and when the power delivery is completed then the controller is configured to generate the second switch driving signal.

17. The power converter of claim 16 wherein the power delivery is completed when a current through the secondary winding drops to zero.

18. The power converter of claim 16 wherein the power delivery from the primary side to the output circuit corresponds to the first switch being OFF, and the controller is configured to generate the second switch driving signal while the first switch is OFF.

19. The power converter of claim 15 wherein the state machine is a pulse width modulation circuit and the first switch driving signal comprises a pulse width modulated voltage signal.

20. The power converter of claim 19 wherein pulse width modulation circuit is configured to modulate a duty cycle of the pulse width modulated voltage signal output from the pulse width modulation circuit based on the received second voltage pulse.

21. The power converter of claim 15 wherein the output characteristic is one or more of an output voltage, an output current, and an output power of the power converter.

22. The power converter of claim 15 further comprising an auxiliary winding coupled to the state machine, wherein the auxiliary winding is magnetically coupled to the secondary winding.

23. The power converter of claim 22 wherein the transformer is configured to transmit the first voltage pulse from the secondary winding to the auxiliary winding using the magnetic coupling between the secondary winding and the auxiliary winding.

24. The power converter of claim 22 wherein the transformer is configured to transmit the first voltage pulse from the secondary winding to the auxiliary winding using a parasitic capacitance between a primary side and a secondary side of the power converter.

25. The power converter of claim 24 wherein the parasitic capacitance comprises a parasitic capacitance of the transformer.

26. The power converter of claim 24 wherein the parasitic capacitance comprises an inherent capacitance of a printed circuit board onto which the power converter is assembled, wherein the inherent capacitance is a result of a component layout on either side of an isolation galvanic barrier.

27. The power converter of claim 15 wherein the first switch comprises a first transistor and the second switch comprises a second transistor.

28. The power converter of claim 15 wherein the sensing circuit comprises a voltage divider circuit.

29. The power converter of claim 15 further comprising a diode coupled in parallel to the second switch and an output capacitor coupled in series to the diode, wherein the diode is configured to enable current flow from the secondary winding to the output capacitor when forward-biased.

30. The power converter of claim 29 wherein when the second switch is ON, an alternative current path is formed between the output capacitor and the secondary winding of the transformer, further wherein a negative secondary current flows from the output capacitor to the secondary winding via the alternative current path, thereby forming the voltage pulse across the secondary winding.

31. The power converter of claim 30 wherein the negative secondary current is generated as discharge from the output capacitor when the alternative current path is formed.

32. The power converter of claim 15 wherein the power converter is configured as one of a flyback-type power converter circuit, a forward-type power converter circuit, a push-pull-type power converter circuit, a half-bridge-type power converter circuit, and a full-bridge-type power converter circuit.