Methods and apparatus for actively snubbing waveforms in switching regulators

• US 6,051,963 A
• Filed: 10/09/1998
• Issued: 04/18/2000
• Est. Priority Date: 10/09/1998
• Status: Expired due to Term

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Linear Technology Corporation (Analog Devices, Inc.)
• Inventors: Eagar, Dale R.
• Primary Examiner(s): Tso, Edward H.
• Assistant Examiner(s): Vu, Bao Q.
• Application Number:
  US09/169,524
• Time in Patent Office: 557 Days
• Field of Search: 363/50, 363/55, 363/56, 323/222, 323/282, 323/284, 323/285
• US Class Current: 323/282
• CPC Class Codes: H02M 1/34 Snubber circuits
• CPC Class Codes: H02M 1/342 Active non-dissipative snubbers
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load
• 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 switching regulator that actively snubs waveforms is provided. The switching regulator includes an inductor, a power switch electrically coupled to the inductor, a first diode electrically coupled to the inductor, and a snubber circuit being coupled in parallel to the inductor. The power switch and the snubber circuit include break-before-make switches such that the power switch is closed only after the snubber switch is opened to initiate a switching cycle, and the snubber switch is closed only after the power switch is opened to provide a decay path for snubbing ringing waveforms.

Claims

1. A method for snubbing waveforms in a switching regulator while maintaining regulator efficiency, said switching regulator including an inductor, a power switch and a rectifying diode electrically coupled to said inductor, a snubber circuit comprising a snubber switch, said snubber circuit being coupled in parallel to said inductor, the method comprising:

beginning a switching cycle by switching said power switch CLOSED while said snubber switch is OPEN;

switching said power switch OPEN while said snubber switch is OPEN;

switching said snubber switch CLOSED while said power switch is OPEN;

decaying current flowing through said inductor via said snubber circuit when said rectifying diode self-commutates so that current in said inductor is prevented from repeatedly changing polarity; and

switching said snubber switch OPEN to end said switching cycle.

2. The method of claim 1, which further comprises preserving energy stored in stray capacitance associated with said power switch so that said preserved energy is provided to said switching regulator at next switching cycle.

3. The method of claim 1, wherein said decaying is characterized by the use of a snubber diode coupled in series with said snubber switch.

4. A switching regulator coupled to an input power supply and having an output node, said switching regulator comprising:

an inductor;

a power switch electrically coupled to said inductor;

a rectifying diode electrically coupled to said inductor;

an output capacitor coupled to said output node; and

a snubber circuit coupled in parallel to said inductor, said snubber circuit comprising a snubber switch that is CLOSED only after said power switch is OPENED to provide a decay path for snubbing ringing waveforms when said rectifying diode self-commutates such that current in said inductor is prevented from repeatedly changing polarity, and such that said power switch is CLOSED only after said snubber switch is OPENED.

5. The switching regulator of claim 4, wherein said rectifying diode is a Schottky diode.

6. The switching regulator of claim 4, wherein said rectifying diode is electrically coupled to said output node.

7. The switching regulator of claim 4, wherein said snubber circuit further comprises a snubber diode coupled in series with said snubber switch.

8. The switching regulator of claim 4, wherein said regulator is a step-up type.

9. The switching regulator of claim 4, wherein said regulator is a step-down type.

10. The switching regulator of claim 4, wherein said regulator is a voltage-inverter type.

11. A switching regulator coupled to an input power supply and having an output node, said switching regulator comprising:

a transistor having stray capacitance and parasitic diode characteristics associated therewith;

an inductor electrically coupled to said transistor;

a rectifying diode electrically coupled to said inductor;

an output capacitor electrically coupled to said output node; and

a snubber circuit coupled in parallel to said inductor, said snubber circuit comprising a snubber diode in series with a snubber switch, said snubber switch being CLOSED a first preselected delay after said transistor is OPENED to provide a decay path for snubbing ringing waveforms associated with said transistor, said decay path being provided when said rectifying diode self-commutates such that current in said inductor is prevented from repeatedly changing polarity, and said transistor being CLOSED a second preselected delay after said snubber switch is OPENED.

12. The switching regulator of claim 11, wherein said rectifying diode is a Schottky diode.

13. The switching regulator of claim 11, wherein said rectifying diode is electrically coupled to said output node.

14. The switching regulator of claim 11, wherein said inductor is electrically coupled to said output node.

15. The switching regulator of claim 11, wherein said regulator is a step-down type.

16. The switching regulator of claim 11, wherein said regulator is a voltage-inverter type.

17. The switching regulator of claim 11, wherein said first and second preselected delays are substantially the same.

18. A switching regulator coupled to an input power supply and having an output node, said switching regulator comprising:

a transistor having output capacitance and parasitic diode characteristics associated therewith;

an inductor electrically coupled to said transistor;

a rectifying element electrically coupled to said inductor;

an output capacitor electrically coupled to said output node; and

a snubber circuit coupled in parallel to said inductor, said snubber circuit comprising a snubber diode in series with a snubber switch, said snubber switch being CLOSED after said transistor is OPENED and a voltage across said inductor approaches zero to provide a decay path for snubbing ringing waveforms associated with the regulator, said decay path being provided when said rectifying diode self-commutates such that current in said inductor is prevented from repeatedly changing polarity, said transistor being CLOSED a preselected delay after said snubber switch is OPENED.