Method and apparatus for extending zero-voltage switching range in a DC to DC converter

• US 8,873,252 B2
• Filed: 03/25/2009
• Issued: 10/28/2014
• Est. Priority Date: 03/26/2008
• Status: Active Grant

• Current Assignee: Enphase Energy Incorporated
• Original Assignee: Enphase Energy Incorporated
• Inventors: Fornage, Martin
• Primary Examiner(s): Berhane, Adolf
• Assistant Examiner(s): GBLENDE, JEFFREY A
• Application Number:
  US12/383,497
• Publication Number:
  US 20090244929A1
• Time in Patent Office: 2,043 Days
• Field of Search: 323/235, 323/298, 323/319, 323/234, 323/318, 363/21.02, 363/21.04, 363/21.12, 363/15, 363/16, 363/21.03
• US Class Current: 363/21.03
• CPC Class Codes: H02M 3/335 using semiconductor devices only
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence
• CPC Class Codes: H02M 7/42 Conversion of dc power input into ac power output without possibility of reversal
• CPC Class Codes: H02M 7/4807 having a high frequency intermediate AC stage
• CPC Class Codes: H02M 7/4815 Resonant converters H02M7/4811 and H02M7/4826 take 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

Apparatus for extending a zero voltage switching (ZVS) range during DC/DC power conversion. The apparatus comprises a DC/DC converter, operated in a quasi-resonant mode, comprising (i) a transformer, (ii) a primary switch, coupled to a primary winding of the transformer, for controlling current flow through the primary winding, and (iii) a varactor, coupled to the transformer, for accelerating a downswing in a voltage across the primary switch.

Claims

1. Apparatus for extending a zero voltage switching (ZVS) range during DC/DC power conversion, comprising:

a DC/DC converter, operated in a quasi-resonant mode, comprising (i) a transformer, (ii) a primary switch, coupled to a primary winding of the transformer, for controlling current flow through the primary winding, and (iii) a varactor coupled to the transformer, wherein during a downswing in voltage across the primary switch, the varactor is passively tuned by a change in voltage across the varactor that changes a capacitance of the varactor, and such tuning causes a resonant frequency of the DC/DC converter to change, wherein the change in the resonant frequency causes the downswing to accelerate.

2. The apparatus of claim 1, wherein the varactor is coupled to a secondary winding of the transformer.

3. The apparatus of claim 1, further comprising a voltage clamp circuit coupled across the primary switch for limiting the voltage across the primary switch, wherein the voltage clamp circuit comprises the varactor.

4. The apparatus of claim 1, wherein the DC/DC converter further comprises a diode and an output capacitor, wherein (i) an anode terminal of the diode is coupled to a first terminal of a secondary winding of the transformer and a first terminal of the varactor, (ii) a first terminal of the output capacitor is coupled to a cathode terminal of the diode, a second terminal of the varactor, and a first output terminal of the DC/DC converter, and (iii) a second terminal of the output capacitor is coupled to a second terminal of the secondary winding and a second output terminal of the DC/DC converter, wherein the first and the second output terminals of the DC/DC converter provide an output voltage.

5. The apparatus of claim 1, wherein the DC/DC converter further comprises an output capacitor, wherein (i) a first terminal of a secondary winding of the transformer is coupled to a first terminal of the varactor, (ii) a first terminal of the output capacitor is coupled to a second terminal of the varactor and a first output terminal of the DC/DC converter, and (iii) a second terminal of the output capacitor is coupled to a second terminal of the secondary winding and a second output terminal of the DC/DC converter, wherein the first and the second output terminals of the DC/DC converter provide an output voltage.

6. The apparatus of claim 1, wherein the DC/DC converter further comprises a diode, a capacitor, and a resistor, wherein (i) an anode terminal of the diode is coupled to a first terminal of the varactor and a drain terminal of the primary switch, (ii) a cathode terminal of the diode is coupled to a second terminal of the varactor, a first terminal of the capacitor, and a first terminal of the resistor, and (iii) a second terminal of the resistor is coupled to a second terminal of the capacitor and a source terminal of the primary switch.

7. The apparatus of claim 1, wherein the DC/DC converter further comprises a capacitor and a resistor, wherein (i) a first terminal of the varactor is coupled to a drain terminal of the primary switch, (ii) a second terminal of the varactor is coupled to a first terminal of the capacitor and a first terminal of the resistor, and (iii) a second terminal of the resistor is coupled to a second terminal of the capacitor and a source terminal of the primary switch.

8. An inverter for extending a zero voltage switching (ZVS) range during DC/AC power conversion, comprising:

a DC/DC converter for converting DC input power to DC output power, the DC/DC converter operated in a quasi-resonant mode and comprising (i) a transformer, (ii) a primary switch, coupled to a primary winding of the transformer, for controlling current flow through the primary winding, and (iii) a varactor coupled to the transformer, wherein during a downswing in voltage across the primary switch, the varactor is passively tuned by a change in voltage across the varactor that changes a capacitance of the varactor, and such tuning causes a resonant frequency of the DC/DC converter to change, wherein the change in the resonant frequency causes the downswing to accelerate; and

a DC/AC conversion module for converting the DC output power to AC output power.

9. The inverter of claim 8, wherein the varactor is coupled to a secondary winding of the transformer.

10. The inverter of claim 8, further comprising a voltage clamp circuit coupled across the primary switch for limiting the voltage across the primary switch, wherein the voltage clamp circuit comprises the varactor.

11. The inverter of claim 8, wherein the DC/DC converter further comprises a diode and an output capacitor, wherein (i) an anode terminal of the diode is coupled to a first terminal of a secondary winding of the transformer and a first terminal of the varactor, (ii) a first terminal of the output capacitor is coupled to a cathode terminal of the diode, a second terminal of the varactor, and a first output terminal of the DC/DC converter, and (iii) a second terminal of the output capacitor is coupled to a second terminal of the secondary winding and a second output terminal of the DC/DC converter, wherein the first and the second output terminals of the DC/DC converter provide an output voltage.

12. The inverter of claim 8, wherein the DC/DC converter further comprises an output capacitor, wherein (i) a first terminal of a secondary winding of the transformer is coupled to a first terminal of the varactor, (ii) a first terminal of the output capacitor is coupled to a second terminal of the varactor and a first output terminal of the DC/DC converter, and (iii) a second terminal of the output capacitor is coupled to a second terminal of the secondary winding and a second output terminal of the DC/DC converter, wherein the first and the second output terminals of the DC/DC converter provide an output voltage.

13. The inverter of claim 8, wherein the DC/DC converter further comprises a diode, a capacitor, and a resistor, wherein (i) an anode terminal of the diode is coupled to a first terminal of the varactor and a drain terminal of the primary switch, (ii) a cathode terminal of the diode is coupled to a second terminal of the varactor, a first terminal of the capacitor, and a first terminal of the resistor, and (iii) a second terminal of the resistor is coupled to a second terminal of the capacitor and a source terminal of the primary switch.

14. The inverter of claim 8, wherein the DC/DC converter further comprises a capacitor and a resistor, wherein (i) a first terminal of the varactor is coupled to a drain terminal of the primary switch, (ii) a second terminal of the varactor is coupled to a first terminal of the capacitor and a first terminal of the resistor, and (iii) a second terminal of the resistor is coupled to a second terminal of the capacitor and a source terminal of the primary switch.

15. A method for extending a zero voltage switching (ZVS) range during DC/DC power conversion, comprising:

deactivating a primary switch of a DC/DC converter operating in quasi-resonant mode, the primary switch for controlling current flow through a primary winding of the DC/DC converter;

increasing a resonant frequency of a resonant circuit of the DC/DC converter during a downswing in a voltage across the primary switch, wherein the resonant frequency is increased by passively tuning, during the downswing, a varactor coupled to a transformer of the DC/DC converter; and

accelerating the downswing of the voltage across the primary switch as a result of increasing the resonant frequency by changing a voltage across the varactor to change the capacitance of the varactor.

16. The method of claim 15, wherein the varactor is coupled to a secondary winding of the transformer.

17. The method of claim 15, further comprising limiting a spike in the voltage across the primary switch, wherein the limiting is performed by a voltage clamp circuit coupled across the primary switch, wherein the voltage clamp circuit comprises the varactor.