Double-clamped ZVS buck-boost power converter

• US 7,920,391 B1
• Filed: 07/10/2009
• Issued: 04/05/2011
• Est. Priority Date: 09/15/2005
• Status: Active Grant

• Current Assignee: Vicor Corporation
• Original Assignee: VLT Incorporated (Vicor Corporation)
• Inventors: Vinciarelli, Patrizio
• Primary Examiner(s): Vu; Bao Q
• Assistant Examiner(s): Zhang; Jue
• Application Number:
  US12/501,112
• Time in Patent Office: 634 Days
• Field of Search: 323/222, 323/224, 323/282, 323/283, 363/16, 363/17
• US Class Current: 363/17
• CPC Class Codes: H02M 1/34 Snubber circuits
• CPC Class Codes: H02M 1/4241 using a resonant converter
• CPC Class Codes: H02M 3/01 Resonant DC/DC converters
• CPC Class Codes: H02M 3/33569 having several active switching elements H02M3/3353 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 transformer-coupled buck-boost DC-DC power converter is disclosed. An active clamp circuit is provided to form a resonant circuit with the transformer to control the slew rate of the secondary current and allow the secondary switch to be turned ON at conditions of zero voltage and relatively low current. The characteristic resonant period of the active clamp transformer circuit may be less than the minimum converter operating period. A winding of the transformer is shunted during a clamp phase to retain energy in the transformer. ZVS phases are provided to reduce switching losses when switches in the converter are turned ON. An energy-storage phase may be varied to control the amount of energy stored per operating cycle. An input-storage phase may transfer energy to the clamp capacitor during a series of converter operating cycles and transfer said energy to the secondary during different converter operating cycles.

Claims

1. Apparatus for converting power from an input source at an input voltage for delivery to a load at an output voltage, the apparatus comprising,

a transformer having a primary winding and a secondary winding,

secondary circuit elements connected to the secondary winding adapted to deliver power to the load at the output voltage,

a first switch connected between a first terminal of the input source and a first terminal of the primary winding,

a second switch connected between a second terminal of the input source and the first terminal of the primary winding,

a clamp circuit including a clamp capacitor connected in series with a clamp switch to provide a current path between a first terminal and a second terminal through the clamp capacitor when the clamp switch is closed and to open the current path through the clamp capacitor when the clamp switch is open;

a fixed connection between the first terminal of the clamp circuit and a second terminal of the primary winding;

a fixed connection between the second terminal of the clamp circuit and the input source;

a fourth switch connected between the second terminal of the input source and the second terminal of the primary winding, and

a switch controller adapted to operate the switches in a series of converter operating cycles, each converter operating cycle comprising (a) an energy-storage phase during which;

the primary winding is connected to the input source by conduction of the first and fourth switches, energy is transferred from the input source to the transformer, and current in the secondary winding is essentially zero.

2. The apparatus of claim 1 wherein each converter operating cycle further comprises:

(b) an energy-transfer phase characterized by a transfer of energy from the transformer to the load and by a transfer of energy between the transformer and the clamp capacitor and by conduction of the second and clamp switches.

3. Apparatus for converting power from an input source at an input voltage for delivery to a load at an output voltage, the apparatus comprising,

a transformer having a primary winding and a secondary winding,

secondary circuit elements connected to the secondary winding adapted to deliver power to the load at the output voltage,

a first switch connected between a first terminal of the input source and a first terminal of the primary winding,

a second switch connected between a second terminal of the input source and the first terminal of the primary winding,

a clamp circuit including a clamp capacitor connected in series with a clamp switch to provide a current path between a first terminal and a second terminal through the clamp capacitor when the clamp switch is closed and to open the current path through the clamp capacitor when the clamp switch is open;

a fixed connection between the first terminal of the clamp circuit and a second terminal of the primary winding;

a fixed connection between the second terminal of the clamp circuit and the input source;

a fourth switch connected between the second terminal of the input source and the second terminal of the primary winding, and

a switch controller adapted to operate the switches in a series of converter operating cycles, each converter operating cycle comprising

(a) an energy-storage phase during which;

the primary winding is connected to the input source by conduction of the first and fourth switches, energy is transferred from the input source to the transformer,

(b) an energy-transfer phase characterized by a transfer of energy from the transformer to the load and by a transfer of energy between the transformer and the clamp capacitor and by conduction of the second and clamp switches; and

wherein the secondary circuit elements comprise rectification circuitry connected between the secondary winding and the load, and wherein the rectification circuitry conducts current during the energy-transfer phase and blocks current throughout the energy-storage phase.

4. Apparatus for converting power from an input source at an input voltage for delivery to a load at an output voltage, the apparatus comprising,

a transformer having a primary winding and a secondary winding,

secondary circuit elements connected to the secondary winding adapted to deliver power to the load at the output voltage,

a first switch connected between a first terminal of the input source and a first terminal of the primary winding,

a second switch connected between a second terminal of the input source and the first terminal of the primary winding,

a clamp circuit including a clamp capacitor connected in series with a clamp switch to provide a current path between a first terminal and a second terminal through the clamp capacitor when the clamp switch is closed and to open the current path through the clamp capacitor when the clamp switch is open;

a fixed connection between the first terminal of the clamp circuit and a second terminal of the primary winding;

a fixed connection between the second terminal of the clamp circuit and the input source;

a fourth switch connected between the second terminal of the input source and the second terminal of the primary winding, and

a switch controller adapted to operate the switches in a series of converter operating cycles, each converter operating cycle comprising

(a) an energy-storage phase during which;

the primary winding is connected to the input source by conduction of the first and fourth switches, energy is transferred from the input source to the transformer, and

(b) an energy-transfer phase characterized by a transfer of energy from the transformer to the load and by a transfer of energy between the transformer and the clamp capacitor and by conduction of the second and clamp switches;

wherein an average value of primary current flows in the primary winding, the average value of primary current having a polarity and being taken over the duration of the energy-storage phase, and

each converter operating cycle further comprises;

(c) a clamp phase during which the primary winding of the transformer is clamped by conduction of the second and fourth switches, the clamp phase being characterized by an essentially zero voltage across the primary winding and an average value of current flowing in the primary winding, the average value of current being taken over the duration of the clamp phase and having a polarity opposite of the polarity of the average value of current during the energy-storage phase immediately preceding the clamp phase.

5. Apparatus for converting power from an input source at an input voltage for delivery to a load at an output voltage, the apparatus comprising,

a transformer having a primary winding and a secondary winding,

secondary circuit elements connected to the secondary winding adapted to deliver power to the load at the output voltage,

a first switch connected between a first terminal of the input source and a first terminal of the primary winding,

a second switch connected between a second terminal of the input source and the first terminal of the primary winding,

a clamp circuit including a clamp capacitor connected in series with a clamp switch to provide a current path between a first terminal and a second terminal through the clamp capacitor when the clamp switch is closed and to open the current path through the clamp capacitor when the clamp switch is open;

a fixed connection between the first terminal of the clamp circuit and a second terminal of the primary winding;

a fixed connection between the second terminal of the clamp circuit and the input source;

a fourth switch connected between the second terminal of the input source and the second terminal of the primary winding,

a switch controller adapted to operate the switches in a series of converter operating cycles, each converter operating cycle comprising

(a) an energy-storage phase during which;

the primary winding is connected to the input source by conduction of the first and fourth switches, energy is transferred from the input source to the transformer,

(b) an energy-transfer phase characterized by a transfer of energy from the transformer to the load and by a transfer of energy between the transformer and the clamp capacitor and by conduction of the second and clamp switches, and

(c) a clamp phase during which the primary winding of the transformer is clamped by conduction of the second and fourth switches, the clamp phase being characterized by essentially zero voltage across said primary winding.

6. The apparatus of claim 2 wherein each converter operating cycle further comprises a zero-voltage switching phase at the end of the energy-storage phase.

7. The apparatus of claim 2 wherein each converter operating cycle further comprises a zero-voltage switching phase at the end of the energy-transfer phase.

8. The apparatus of claim 4 or 5 wherein each converter operating cycle further comprises a zero-voltage switching phase at the end of the clamp phase.

9. A method of converting power from an input source at an input voltage for delivery to a load at an output voltage, via a transformer having a primary winding and a secondary winding, the method comprising:

providing secondary circuit elements connected to the secondary winding adapted to deliver power to the load at the output voltage,

providing a first switch connected between a first terminal of the input source and a first terminal of the primary winding,

providing a second switch connected between a second terminal of the input source and the first terminal of the primary winding,

providing a clamp circuit including a clamp capacitor connected in series with a clamp switch to provide a current path between a first terminal and a second terminal through the clamp capacitor when the clamp switch is closed and to open the current path through the clamp capacitor when the clamp switch is open;

providing a fixed connection between the first terminal of the clamp circuit and a second terminal of the primary winding;

providing a fixed connection between the second terminal of the clamp circuit and the input source;

providing a fourth switch connected between the second terminal of the input source and the second terminal of the primary winding,

operating the switches in a series of converter operating cycles,

(a) establishing an energy-storage phase of the converter operating cycles during which the primary winding is connected to the input source by conduction of the first and fourth switches, the energy-storage phase being characterized by a transfer of energy from the input source to the transformer, and

essentially preventing current flow in the secondary winding throughout the energy-storage phase.

10. The method of claim 9 further comprising:

(b) establishing an energy-transfer phase of the converter operating cycles characterized by a transfer of energy from the transformer to the load, by a transfer of energy between the transformer and the clamp capacitor, and by conduction of the second and clamp switches.

11. The method of claim 10 wherein the secondary circuit elements comprise rectification circuitry connected between the secondary winding and the load, and further comprising configuring the rectification circuitry to conduct current during the energy-transfer phase and to block current throughout the energy-storage phase.

12. The method of claim 10 wherein:

an average value of primary current flows in the primary winding, the average value of primary current having a polarity and being taken over the duration of the energy-storage phase, and

further comprising;

(c) establishing a clamp phase of the converter operating cycles during which the primary winding of the transformer is clamped by conduction of the second and fourth switches, the clamp phase being characterized by an essentially zero voltage across the primary winding and an average value of current flowing in the primary winding, the average value of current being taken over the duration of the clamp phase and having a polarity opposite of the polarity of the average value of current during the energy-storage phase immediately preceding the clamp phase.

13. The method of claim 10 further comprising:

establishing a clamp phase of the converter operating cycles during which the primary winding of the transformer is clamped by conduction of the second and fourth switches, the clamp phase being characterized by essentially zero voltage across said primary winding.

14. The method of claim 10 further comprising establishing a zero-voltage switching phase of the converter operating cycles at the end of the energy-storage phase.

15. The method of claim 10 further comprising establishing a zero-voltage switching phase of the converter operating cycles at the end of the energy-transfer phase.

16. The method of claim 12 or 13 further comprising establishing a zero voltage switching phase of the converter operating cycles at the end of the clamp phase.

17. The method of claim 11 wherein the clamp circuit is connected to the second terminal of the input source.

18. The apparatus of claim 3 wherein the clamp circuit is connected to the second terminal of the input source.