AC/DC converter with power factor correction

• US 7,149,097 B1
• Filed: 08/17/2005
• Issued: 12/12/2006
• Est. Priority Date: 08/17/2005
• Status: Active Grant

• Current Assignee: Chemtron Research LLC (Intellectual Ventures LLC)
• Original Assignee: Synditec Inc. (Million Star Technology Ltd.)
• Inventors: Rodriguez, Harry, Shteynberg, Anatoly
• Primary Examiner(s): Riley, Shawn
• Application Number:
  US11/206,356
• Time in Patent Office: 482 Days
• Field of Search: 363/16, 363/89, 363/127
• US Class Current: 363/16
• CPC Class Codes: H02M 1/4258 using a single converter stage both for correction of AC input power factor and generation of a regulated and galvanically isolated DC output voltage H02M1/4241 takes precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A switch mode AC/DC converter with input current shaped for unity power factor. Input current is modulated by input voltage, and input inductor and isolation transformer are driven with the same duty ratio, with a low voltage across bulk capacitor. This voltage is determined only by input voltage amplitude. Energy stored in the leakage inductance of the transformer is returned back to the internal DC source. A soft switching circuit is connected to the primary side, eliminating the need for high side drive. Sources of the main and auxiliary switches and primary winding of the transformer are connected to ground for easy primary voltage sensing. Overvoltage protection circuit of the output is connected to exclusively primary side signals. Secondary synchronous rectifier is driven by a circuit synchronized with the system clock. The circuit can be coupled to either the primary or the secondary winding of the isolation transformer.

Claims

1. A switch mode AC/DC converter, comprising:

an input inductor, comprising a first terminal and a second terminal;

a rectifier, comprising a positive terminal coupled to the first terminal of the input inductor, and a negative terminal coupled to a ground node;

a switch, comprising a first terminal coupled to the second terminal of the input inductor, a second terminal coupled to the ground node, and a control terminal;

a bulk capacitor, comprising a positive terminal coupled to the first terminal of the switch, and a negative terminal;

an isolation transformer, comprising a first terminal of a primary winding coupled to the second terminal of the switch, a second terminal of the primary winding coupled to the negative terminal of the bulk capacitor, and a secondary winding coupled to a load;

an isolating diode, comprising an anode coupled to the negative terminal of the bulk capacitor, and a cathode coupled to the first terminal of the input inductor; and

a control system coupled to a control terminal of the switch, comprising a feedback loop.

2. The converter of claim 1, wherein the feedback loop comprises an output voltage feedback loop coupled to the secondary winding of the isolation transformer.

3. The converter of claim 1, further comprising:

a second isolating diode, comprising an anode coupled to the isolation transformer, and a cathode coupled to the bulk capacitor; and

a blocking diode coupled between the secondary winding of the isolation transformer and the load.

4. The converter of claim 3, further comprising:

a diode, comprising a cathode coupled to an AC terminal, and an anode; and

a resister coupled to the anode of the diode and the negative terminal of the bulk capacitor.

5. The converter of claim 1, further comprising a leakage energy recovery circuit, comprising:

a diode, a first capacitor, and a second capacitor coupled across the primary winding of the isolation transformer.

6. The converter of claim 5, wherein when the switch is off, energy stored in a leakage inductance of the isolation transformer is transferred to the first and second capacitors.

7. The converter of claim 5, further comprising:

the input inductor further comprising an overwinding coupled to the ground node, wherein the overwinding has same number of turns as a main winding;

a second isolation diode, comprising an anode coupled to the isolation transformer, and a cathode coupled to the bulk capacitor; and

a third isolation diode, comprising a cathode coupled to the overwinding of the input inductor, and an anode coupled to a cathode of the diode.

8. The converter of claim 5, further comprising:

the feedback loop, comprising a closed feedback loop coupled to the primary winding of the isolation transformer; and

a synchronous rectifier element coupled between the secondary winding of the isolation transformer and a positive terminal of the output.

9. The converter of claim 8, wherein the synchronous rectifier element comprises:

a second switch, comprising a control terminal coupled to a secondary control circuit, wherein the secondary control circuit is coupled to a second secondary winding of the isolation transformer.

10. The converter of claim 5, further comprising:

a winding, comprising a first terminal coupled to a cathode of the diode and a second terminal;

a second isolation diode, comprising a cathode coupled to the positive terminal of the capacitor, and an anode coupled to the second terminal of the winding; and

an auxiliary switch coupled between the ground node and the anode of the second isolation diode, comprising a control terminal coupled to the control circuit.

11. The converter of claim 10, wherein when the switch turns off, energy stored in a leakage inductance of the primary winding of the isolation transformer is transferred to the first and second capacitors,

wherein if further stored energy is to be recycled, then the inductance of the primary winding of the isolation transformer is transferred to the first and second capacitors through the winding and the auxiliary switch.

12. The converter of claim 10, wherein the auxiliary switch is bi-directional, allowing a flow of energy from the first and second capacitors into the isolation transformer, enabling a softswitching turn on of the switch, wherein a leakage energy of the winding is returned to the bulk capacitor.

13. The converter of claim 10, wherein the auxiliary switch comprises N-type MOSFETs.

14. The converter of claim 1, further comprising:

a flyback winding coupled to a capacitor and the second terminal of the switch;

the capacitor coupled to the second terminal of the switch; and

a diode, comprising a cathode coupled to the capacitor, and an anode coupled to the flyback winding.

15. The converter of claim 1, further comprising:

the input inductor comprising a secondary winding; and

a second control circuit to drive the secondary winding of the input inductor.

16. The converter of claim 15, wherein the second control circuit comprises:

a peak detector with an input comprising an input voltage;

an integrator with an input comprising a reference voltage;

a comparator with an input comprising an output of the peak detector and an output of the integrator;

an averaging R-C filter coupled to the output of the integrator;

a P-channel FET coupled to the filter, a voltage source, and the secondary winding of the input inductor;

an oscillator; and

an AND3 gate with an input comprising an output of the oscillator and an output from the comparator, and with an output comprising a reset signal.

17. The converter of claim 1, further comprising:

a second switch, comprising a first terminal coupled to the second terminal of the input inductor and to the first terminal of the switch, a second terminal coupled to the negative terminal of the rectifier, and a control terminal coupled to the control circuit.

18. The converter of claim 17, wherein the switch is controlled separately from the second switch.

19. A switch mode AC/DC converter, comprising:

an input inductor, comprising a first terminal and a second terminal;

a rectifier, comprising a positive terminal coupled to the first terminal of the input inductor, and a negative terminal coupled to a ground node;

a switch, comprising a first terminal coupled to the second terminal of the input inductor, a second terminal coupled to the ground node, and a control terminal;

a bulk capacitor, comprising a positive terminal coupled to the first terminal of the switch, and a negative terminal;

an isolation transformer, comprising a first terminal of a primary winding coupled to the second terminal of the switch, a second terminal of the primary winding coupled to the negative terminal of the bulk capacitor, and a secondary winding coupled to a load;

a first isolating diode, comprising an anode coupled to the negative terminal of the bulk capacitor, and a cathode coupled to the first terminal of the input inductor;

a control system coupled to a control terminal of the switch, comprising a feedback loop;

a second isolating diode, comprising an anode coupled to the isolation transformer, and a cathode coupled to the bulk capacitor; and

a blocking diode coupled between the secondary winding of the isolation transformer and the load.

20. A switch mode AC/DC converter, comprising:

an input inductor, comprising a first terminal and a second terminal;

a rectifier, comprising a positive terminal coupled to the first terminal of the input inductor, and a negative terminal coupled to a ground node;

a switch, comprising a first terminal coupled to the second terminal of the input inductor, a second terminal coupled to the ground node, and a control terminal;

a bulk capacitor, comprising a positive terminal coupled to the first terminal of the switch, and a negative terminal;

an isolation transformer, comprising a first terminal of a primary winding coupled to the second terminal of the switch, a second terminal of the primary winding coupled to the negative terminal of the bulk capacitor, and a secondary winding coupled to a load;

a first isolating diode, comprising an anode coupled to the negative terminal of the bulk capacitor, and a cathode coupled to the first terminal of the input inductor;

a control system coupled to a control terminal of the switch, comprising a feedback loop;

a second isolating diode, comprising an anode coupled to the isolation transformer, and a cathode coupled to the bulk capacitor;

a blocking diode coupled between the secondary winding of the isolation transformer and the load;

a diode, comprising a cathode coupled to an AC terminal, and an anode; and

a resister coupled to the anode of the diode and the negative terminal of the bulk capacitor.

21. A switch mode AC/DC converter, comprising:

an input inductor, comprising a first terminal, a second terminal, and an overwinding coupled to a ground node, wherein the overwinding has same number of turns as a main winding of the input inductor;

a rectifier, comprising a positive terminal coupled to the first terminal of the input inductor, and a negative terminal coupled to the ground node;

a switch, comprising a first terminal coupled to the second terminal of the input inductor, a second terminal coupled to the ground node, and a control terminal;

a bulk capacitor, comprising a positive terminal coupled to the first terminal of the switch, and a negative terminal;

an isolation transformer, comprising a first terminal of a primary winding coupled to the second terminal of the switch, a second terminal of the primary winding coupled to the negative terminal of the bulk capacitor, and a secondary winding coupled to a load;

a first isolating diode, comprising an anode coupled to the negative terminal of the bulk capacitor, and a cathode coupled to the first terminal of the input inductor;

a control system coupled to a control terminal of the switch, comprising a feedback loop;

a leakage energy recovery circuit, comprising a diode, a first capacitor, and a second capacitor coupled across the primary winding of the isolation transformer;

a second isolation diode, comprising an anode coupled to the isolation transformer, and a cathode coupled to the bulk capacitor; and

a third isolation diode, comprising a cathode coupled to the overwinding of the input inductor, and an anode coupled to a cathode of the diode.

22. A switch mode AC/DC converter, comprising:

an input inductor, comprising a first terminal, a second terminal, and an overwinding coupled to a ground node, wherein the overwinding has same number of turns as a main winding of the input inductor;

a rectifier, comprising a positive terminal coupled to the first terminal of the input inductor, and a negative terminal coupled to the ground node;

a switch, comprising a first terminal coupled to the second terminal of the input inductor, a second terminal coupled to the ground node, and a control terminal;

a bulk capacitor, comprising a positive terminal coupled to the first terminal of the switch, and a negative terminal;

an isolation transformer, comprising a first terminal of a primary winding coupled to the second terminal of the switch, a second terminal of the primary winding coupled to the negative terminal of the bulk capacitor, and a secondary winding coupled to a load;

a first isolating diode, comprising an anode coupled to the negative terminal of the bulk capacitor, and a cathode coupled to the first terminal of the input inductor;

a control system coupled to a control terminal of the switch, comprising a closed feedback loop coupled to the primary winding of the isolation transformer;

a leakage energy recovery circuit, comprising a diode, a first capacitor, and a second capacitor coupled across the primary winding of the isolation transformer; and

a synchronous rectifier element comprising a second switch, the second switch comprising a control terminal coupled to a secondary control circuit, wherein the second control circuit is coupled to a second secondary winding of the isolation transformer.

23. A switch mode AC/DC converter, comprising:

an input inductor, comprising a first terminal, a second terminal, and an overwinding coupled to a ground node, wherein the overwinding has same number of turns as a main winding of the input inductor;

a rectifier, comprising a positive terminal coupled to the first terminal of the input inductor, and a negative terminal coupled to the ground node;

a switch, comprising a first terminal coupled to the second terminal of the input inductor, a second terminal coupled to the ground node, and a control terminal;

a bulk capacitor, comprising a positive terminal coupled to the first terminal of the switch, and a negative terminal;

an isolation transformer, comprising a first terminal of a primary winding coupled to the second terminal of the switch, a second terminal of the primary winding coupled to the negative terminal of the bulk capacitor, and a secondary winding coupled to a load;

a first isolating diode, comprising an anode coupled to the negative terminal of the bulk capacitor, and a cathode coupled to the first terminal of the input inductor;

a control system coupled to a control terminal of the switch, comprising a feedback loop;

a leakage energy recovery circuit, comprising a diode, a first capacitor, and a second capacitor coupled across the primary winding of the isolation transformer;

a winding, comprising a first terminal coupled to a cathode of the diode and a second terminal;

a second isolation diode, comprising a cathode coupled to the positive terminal of the bulk capacitor, and an anode coupled to the second terminal of the winding; and

an auxiliary switch coupled between the ground node and the anode of the second isolation diode, comprising a control terminal coupled to the control circuit.

24. A switch mode AC/DC converter, comprising:

an input inductor, comprising a first terminal and a second terminal;

a rectifier, comprising a positive terminal coupled to the first terminal of the input inductor, and a negative terminal coupled to a ground node;

a switch, comprising a first terminal coupled to the second terminal of the input inductor, a second terminal coupled to the ground node, and a control terminal;

a bulk capacitor, comprising a positive terminal coupled to the first terminal of the switch, and a negative terminal;

an isolation transformer, comprising a first terminal of a primary winding coupled to the second terminal of the switch, a second terminal of the primary winding coupled to the negative terminal of the bulk capacitor, and a secondary winding coupled to a load;

an isolating diode, comprising an anode coupled to the negative terminal of the bulk capacitor, and a cathode coupled to the first terminal of the input inductor;

a control system coupled to a control terminal of the switch, comprising a feedback loop;

a flyback winding coupled to a capacitor and the second terminal of the switch;

the capacitor coupled to the second terminal of the switch; and

a diode, comprising a cathode coupled to the capacitor, and an anode coupled to the flyback winding.

25. A switch mode AC/DC converter, comprising:

an input inductor, comprising a first terminal, a second terminal, a primary winding, and a secondary winding;

a rectifier, comprising a positive terminal coupled to the first terminal of the input inductor, and a negative terminal coupled to a ground node;

a switch, comprising a first terminal coupled to the second terminal of the input inductor, a second terminal coupled to the ground node, and a control terminal;

a bulk capacitor, comprising a positive terminal coupled to the first terminal of the switch, and a negative terminal;

an isolation transformer, comprising a first terminal of a primary winding coupled to the second terminal of the switch, a second terminal of the primary winding coupled to the negative terminal of the bulk capacitor, and a secondary winding coupled to a load;

an isolating diode, comprising an anode coupled to the negative terminal of the bulk capacitor, and a cathode coupled to the first terminal of the input inductor;

a first control system coupled to a control terminal of the switch, comprising a feedback loop; and

a second control circuit to drive the secondary winding of the input inductor, wherein the second control circuit comprises;

a peak detector with an input comprising an input voltage,

an integrator with an input comprising a reference voltage,

a comparator with an input comprising an output of the peak detector and an output of the integrator,

an average R-C filter coupled to the output of the integrator,

a P-channel FET coupled to the filter, a voltage source, and the secondary winding of the input inductor,

an oscillator, and

an AND3 gate with an input comprising an output of the oscillator and an output from the comparator, and with an output comprising a reset signal.

26. A switch mode AC/DC converter, comprising:

an input inductor, comprising a first terminal and a second terminal;

a rectifier, comprising a positive terminal coupled to the first terminal of the input inductor, and a negative terminal coupled to a ground node;

a first switch, comprising a first terminal coupled to the second terminal of the input inductor, a second terminal coupled to the ground node, and a control terminal;

a bulk capacitor, comprising a positive terminal coupled to the first terminal of the first switch, and a negative terminal;

an isolation transformer, comprising a first terminal of a primary winding coupled to the second terminal of the first switch, a second terminal of the primary winding coupled to the negative terminal of the bulk capacitor, and a secondary winding coupled to a load;

an isolating diode, comprising an anode coupled to the negative terminal of the bulk capacitor, and a cathode coupled to the first terminal of the input inductor;

a control system coupled to a control terminal of the first switch, comprising a feedback loop; and

a second switch, comprising a first terminal coupled to the second terminal of the input inductor and to the first terminal of the first switch, a second terminal coupled to the negative terminal of the rectifier, and a control terminal coupled to the control circuit, wherein the first switch is controlled separately from the second switch.

27. A method for controlling secondary synchronous rectification for a switch mode AC/DC converter, comprising:

(a) coupling a synchronous rectifier element between a secondary winding of an isolation transformer and a positive terminal of an output, wherein a control terminal of the synchronous rectifier element is coupled to a control circuit, wherein an integrator of the control circuit is charged during a positive voltage swing of the secondary winding;

(b) resetting the integrator at a negative swing of the secondary winding, wherein when the integrator reaches zero volts, positive and negative voltseconds of the isolation transformer are balanced;

(c) activating a logic of the control circuit when the integrator reaches zero volts;

(d) turning the synchronous rectifier element off by the activated logic, wherein there is a delay between time logic is activated and time the synchronous rectifier element is turned off, wherein during the delay, negative current is allowed through the synchronous rectifier element, such that a collapse of the voltage across the isolation transformer is delayed; and

(e) sensing an output voltage during a sense window, wherein the sense window comprises the time the integrator reaches zero volts and an end of the delay.

28. A method for controlling secondary synchronous rectification for a switch mode AC/DC converter, comprising:

(a) coupling a synchronous rectifier element between a primary winding of an isolation transformer and a positive terminal of an output, wherein a control terminal of the synchronous rectifier element is coupled to a control circuit, wherein an integrator of the control circuit is charged during a positive voltage swing of the primary winding;

(b) resetting the integrator at a negative swing of the primary winding, wherein when the integrator reaches zero volts, positive and negative voltseconds of the isolation transformer are balanced;

(c) activating a logic of the control circuit when the integrator reaches zero volts;

(d) turning the synchronous rectifier element off by the activated logic, wherein there is a delay between time logic is activated and time the synchronous rectifier element is turned off, wherein during the delay, negative current is allowed through the synchronous rectifier element, such that a collapse of the voltage across the isolation transformer is delayed; and

(e) sensing an output voltage during a sense window as current in a secondary winding of the isolation transformer, wherein the sense window comprises the time the integrator reaches zero volts and an end of the delay.

29. The method of claim 28, wherein the sensing step (e) comprises:

(e1) activating a sample and hold circuit which samples a reflected to primary side output voltage; and

(e2) applying the sampled voltage to an error amplifier.