Active clamp step-down converter with power switch voltage clamping function

• US 6,512,352 B2
• Filed: 06/07/2001
• Issued: 01/28/2003
• Est. Priority Date: 06/07/2001
• Status: Expired due to Fees

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Qian, Jinrong
• Primary Examiner(s): Vu, Bao Q.
• Application Number:
  US09/876,632
• Publication Number:
  US 20020185993A1
• Time in Patent Office: 600 Days
• Field of Search: 323/222, 323/282, 323/901, 323/902, 323/908, 363/21.04, 363/21.08, 363/21.12, 363/21.16
• US Class Current: 323/282
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load
• CPC Class Codes: H03K 17/08142 in field-effect transistor switches

Abstract

A circuit for clamping a voltage across a switching element to a value equal to or less than the sum of the input voltage plus the voltage across a clamping capacitor is provided. The circuit achieves voltage clamping in a circuit configuration in which an active clamp circuit includes a switch and a clamping capacitor connected in parallel with a first winding of a coupled winding. The active clamp prevents the occurrence of voltage spikes across a first switching element. The clamping capacitor serves a second function in that it recovers energy stored in the first winding of the coupled winding.

Claims

1. A converter circuit comprising:

a first switching element S1 connected in series with a DC input source, whereby all current from the source must flow through the first switching element;

a first winding N1 and a second winding N2; and

an active clamp circuit coupled directly and bidirectionally to the first switching element S1, the first winding N1 and the second winding N2 for at least reducing voltage spikes across said first switching element S1.

2. The converter circuit of claim 1, further comprising a second switching element S2 coupled to the first and second windings.

3. The converter circuit of claim 2, further comprising a diode DS connected in parallel with the second switching element S2.

4. The converter circuit of claim 1, wherein said converter circuit further includes a filter capacitor coupled in parallel to a load.

5. The converter circuit of claim 1, wherein said converter is a DC-DC converter.

6. A method of clamping a voltage across a switching element in a converter circuit, said method comprising the steps of:

providing a first switching element S1 connected in series with a DC input source, whereby all current from the source must flow through the first switching element;

providing a first winding N1 and a second winding N2; and

clamping said voltage by directly coupling an active clamp circuit to the first switching element S1, the first winding N1 and the second winding N2 for reducing voltage spikes across said first switching element S1.

7. The method of claim 6, further comprising the step of providing a second switching element S2 coupled to the first and second windings.

8. The method of claim 7, further comprising the step of providing a diode DS connected in parallel with the second switching element S2.

9. The method of claim 6, further comprising the steps of:

providing a clamping capacitor C_r adapted to recover leakage energy from said first winding N1; and

providing a third switching element S3 connected in series with said clamping capacitor C_r;

wherein said clamping capacitor and said third switching element S3 form said clamping circuit.

10. The method of claim 6, wherein said clamping step is performed at a time when said switching element transitions from an ON state to an OFF state.

11. The method of claim 9, wherein said clamping capacitor recovers energy during an OFF state of said switching element.

12. The method of claim 6, wherein first winding N1 has an equivalent leakage inductance L_k, further comprising the step of recovering leakage energy in inductance L_k in each switching cycle.

13. The method of claim 12, wherein the leakage energy in L_k is recovered by charging the clamping capacitor C_r through the body diode D3 of switching element S3.

18. The method of claim 6, further comprising the steps of:

magnetically coupling the windings to each other,

connecting one end of each of said windings to a node therebetween,

connecting the other end of winding N1 to first switching element S1, and

connecting the clamping circuit in parallel with winding N1.

19. The method of claim 18, further comprising the step of connecting a second

14. A converter circuit comprising:

a first switching element S1 connected in series with a DC input source, whereby all current from the source must flow through the first switching element;

a first winding N1 and a second winding N2 each having a respective end connected to a node therebetween, and magnetically coupled to each other, winding N1 having an other end connected to the first switching element; and

an active clamp circuit coupled in parallel with winding N1 to the first switching element S1, and to said node for at least reducing voltage spikes across said first switching element S1.

15. The converter circuit of claim 14, wherein said active clamp circuit comprises a clamping switch S3 in series with a clamping capacitor C_r, said capacitor C_r being arranged to recover leakage energy from said first winding N1.

16. The converter circuit of claim 14, wherein:

said active clamp circuit comprises a clamping switch S3 in series with a clamping capacitor C_r, and

the converter circuit further comprises a second switching element S2 connected between said node and a common bus.

17. The converter circuit of claim 16, further comprising a diode DS connected in parallel with the second switching element S2.