PASSIVE LOSSLESS SNUBBER CELL FOR A POWER CONVERTER

• US 20110057639A1
• Filed: 09/09/2009
• Published: 03/10/2011
• Est. Priority Date: 09/09/2009
• Status: Active Grant

• Current Assignee: City University of Hong Kong
• Original Assignee: City University of Hong Kong
• Inventors: Li, Tin Ho, Chung, Shu Hung
• Granted Patent: US 8,107,268 B2
• Time in Patent Office: Days
• US Class Current: 323/311
• CPC Class Codes: H02M 1/34 Snubber circuits
• CPC Class Codes: H02M 1/346 Passive non-dissipative snubbers
• 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 passive lossless snubber cell for a switched-mode power converter comprises an energy absorbing circuit and an energy resetting circuit coupled to said energy absorbing circuit. The energy absorbing circuit is arranged to release energy stored in a snubber capacitor of the energy absorbing circuit to a storage capacitor of the energy resetting circuit through a resonant pathway of the snubber cell in response to a first switching action of a power converter transistor switch. The energy resetting circuit is arranged to release the energy stored therein to a part of a circuit of the power converter in response to a second switching action of the power converter transistor switch, the second switching action being a successive action to the first switching action. The passive lossless snubber cell has several advantages over existing snubbering techniques. First, it provides zero-current-switching (ZCS) and zero-voltage-switching (ZVS) conditions for turning on and off, respectively, the switch over a wide load range. Second, it does not introduce extra voltage stress on the switch. Third, by taking the ripple current through the switch into account, the peak switch current during the snubber resonance period is designed to be less than the designed switch current without the snubber. Hence, the proposed snubber does not introduce extra current stress on the switch.

Claims

1. A snubber cell for a switched-mode power converter, comprising:

an energy absorbing circuit;

an energy resetting circuit coupled to said energy absorbing circuit;

wherein the energy absorbing circuit is arranged to release energy stored in a snubber capacitor of the energy absorbing circuit to a storage capacitor of the energy resetting circuit through a resonant pathway of the snubber cell in response to a first switching action of a power converter transistor switch and wherein the energy resetting circuit is arranged to release the energy stored therein to a part of a circuit of the power converter in response to a second switching action of the power converter transistor switch, said second switching action being successive to the first switching action.

2. The snubber cell of claim 1, wherein the energy resetting circuit is arranged to release the energy stored therein to a load of the power converter circuit.

3. The snubber cell of claim 1, wherein the storage capacitor of the energy absorbing circuit is arranged to have an energy storage capacity equal to or greater than the energy storage capacity of the snubber capacitor.

4. The snubber cell of claim 1, wherein the energy absorbing circuit is arranged to release energy stored in a snubber inductor to be stored in the snubber capacitor in response to said first switching action prior to the step of releasing said energy from the snubber capacitor to said storage capacitor.

5. The snubber cell of claim 4, wherein the energy resetting circuit is arranged to not commence discharging of the energy stored in the storage capacitor until the snubber inductor is completely discharged.

6. The snubber cell of claim 5, wherein the energy resetting circuit is arranged to not commence discharging of the energy stored in the storage capacitor until the snubber inductor is completely discharged by defining a minimum switch on time and a minimum switch off time for the power converter transistor switch.

7. The snubber cell of claim 4, wherein a saturable inductor is arranged in series with said snubber inductor to further delay a rise in current in the transistor switch.

8. The snubber cell of claim 1, wherein said energy absorbing circuit comprises a snubber inductor arranged in series with the transistor switch of the power converter, the snubber capacitor arranged in parallel with said transistor switch, and a first diode arranged between a node common to the snubber inductor and the transistor switch and a node of said snubber capacitor.

9. The snubber cell of claim 8, wherein said energy resetting circuit comprises a configuration of a second diode, a storage inductor, a third diode, the storage capacitor and a fourth diode, wherein the second and fourth diodes and the storage capacitor couple the energy resetting circuit to the energy absorbing circuit.

10. The snubber cell of claim 1, wherein the snubber cell has first, second and third nodes for connecting to a switched-mode power converter circuit, there being provided a snubber inductor between the first and third nodes, a first diode in series with the snubber capacitor between the third and second nodes, a second diode between the first node and a first common node located between the first diode and the snubber capacitor, the storage capacitor in series with a fourth diode between the first and second nodes, and a storage inductor in series with a third diode between said first common node and a second common node located between the storage capacitor and the fourth diode.

11. A switched-mode power converter having a snubber cell as claimed in any one of claims 1 to 10.

12. The switched-mode power converter of claim 11, wherein said power converter comprises one of:

a buck converter, boost converter, a buck-boost converter, a Cuk converter, a SEPIC, a two-switch forward converter, and a two-switch flyback converter.

13. A method of operating a switched-mode power converter having an energy absorbing circuit and an energy resetting circuit coupled to said energy absorbing circuit, the method comprising:

releasing energy stored in a snubber capacitor of the energy absorbing circuit to a storage capacitor of the energy resetting circuit through a resonant pathway of the snubber cell in response to a first switching action of a transistor switch of the power converter; and

releasing the energy stored in the storage capacitor to a part of a circuit of the power converter in response to a second switching action of the power converter transistor switch, said second switching action being successive to the first switching action.

14. The method of claim 13, wherein it comprises not commencing discharging of the energy stored in the storage capacitor until a snubber inductor is completely discharged.

15. The method of claim 14, wherein it comprises not commencing discharging of the energy stored in the storage capacitor until the snubber inductor is completely discharged by maintaining the transistor switch on for a defined minimum switch on time and maintaining the switch off for a defined minimum switch off time.

16. The method of claim 14, wherein it comprises providing a saturable inductor in series with said snubber inductor to further delay a rise in current in the transistor switch.