Systems and methods for conserving energy in a switching circuit

• US 6,809,503 B1
• Filed: 01/13/2003
• Issued: 10/26/2004
• Est. Priority Date: 01/13/2003
• Status: Active Grant

• 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): Vu, Bao Q.
• Application Number:
  US10/342,415
• Time in Patent Office: 652 Days
• Field of Search: 323/222, 323/282, 323/284, 323/351, 323/265
• US Class Current: 323/222
• CPC Class Codes: H02M 1/34 Snubber circuits
• CPC Class Codes: H02M 1/342 Active non-dissipative snubbers
• CPC Class Codes: H02M 3/005 using Cuk converters
• CPC Class Codes: H02M 3/155 using semiconductor devices only
• 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 switch recovery circuit is disclosed for improving the efficiency of switching voltage regulators. The switch recovery circuit includes a first and second inductor, a capacitor, a first diode, and a recovery circuit. The capacitor and diode comprise an AC coupled loop circuit around the first inductor. Current flows through the loop circuit soon after the switch is opened and charges the capacitor. The recovery circuit, which includes a second inductor that is magnetically coupled to the first inductor, provides current, at least some of which discharges the capacitor (i.e. current that flows in the opposite direction to the loop current) after the loop current stops. A second diode is interposed in series with the second inductor to provide appropriate voltage offsets in the circuit and to prevent the first inductor from being shorted to ground through the second inductor.

Claims

1. A switch recovery circuit for use in conjunction with a switch and an input energy source, comprising:

a first inductor coupled between the switch and the input energy source;

a second inductor magnetically coupled to said first inductor;

a first capacitor with first and second terminals coupled between said first and second inductors such that said first terminal is associated with said first inductor and said second terminal is associated with said second inductor;

a first switching device coupled to said second inductor such that said switching device is capable of preventing current from flowing through said second inductor in at least one direction;

wherein

the polarity of the magnetic coupling between said first inductor and said second inductor is such that changes in voltage across said first inductor with respect to said first terminal of said capacitor correspond to the same polarity changes in voltage across said second inductor with respect to said second terminal of the capacitor; and

said first inductor is coupled to said first capacitor such that current flows from said first inductor to said first capacitor at least at some point in time while said switch is open.

2. The switch recovery circuit of claim 1 wherein said first and second inductors are wound to the same magnetic core.

3. The switch recovery circuit of claim 2 wherein the ratio of windings of said second inductor to said first inductor is N:

1, where N is greater than 1.

4. The switch recovery circuit of claim 1 wherein said first switching device comprises a diode coupled to prevent current from flowing from said first capacitor through said second inductor.

5. The switch recovery circuit of claim 1 further comprising a second switching device coupled between said first inductor and said first capacitor such that current may flow through said first inductor, first capacitor and said second switching device.

6. The switch recovery circuit of claim 1 further comprising:

a second capacitor coupled to said second inductor at a first node; and

a third inductor coupled to both said second capacitor and said second inductor at said first node.

7. The switch recovery circuit of claim 6 wherein said third inductor is magnetically coupled to said first and second inductors such that changes in voltage across said first inductor with respect to said first terminal of said capacitor correspond to the same polarity changes in voltage across said third inductor.

8. The switch recovery circuit of claim 1 further comprising a current source coupled to said switch and said first inductor.

15. The switch recovery circuit of claim 6 wherein said third inductor is magnetically coupled to said first and second inductors such that changes in voltage across said first inductor with respect to said first terminal of said capacitor correspond to the same polarity changes in voltage across said third inductor.

9. A switch recovery circuit for use in conjunction with a switch and an input energy source, comprising:

a first inductor coupled between said switch and said input energy source;

a second inductor magnetically coupled to said first inductor;

a first capacitor with first and second terminals coupled between said first and second inductors such that said first terminal is associated with said first inductor and said second terminal is associated with said second inductor;

wherein

the polarity of the magnetic coupling between said first inductor and said second inductor is such that changes in voltage across said first inductor with respect to said first terminal of said capacitor correspond to the same polarity changes in voltage across said second inductor with respect to said second terminal of said capacitor;

the magnetic coupling between said first and second inductors is such that the voltage across said first inductor corresponds to a greater voltage across said second inductor;

said first inductor is coupled to said first capacitor such that current flows from said first inductor to said first capacitor at least at some point in time while said switch is open.

10. The switch recovery circuit of claim 9 further comprising a first switching device coupled to said second inductor such that said first switching device prevents current from flowing from said first capacitor through said second inductor at least at some point in time while said switch is open.

11. The switch recovery circuit of claim 10 wherein said first switching device comprises a diode.

12. The switch recovery circuit of claim 9 wherein said first and second inductors are wound to the same magnetic core.

13. The switch recovery circuit of claim 9 further comprising a first switching device coupled between said first inductor and said first capacitor such that current may flow through said first inductor, first capacitor and said second switching device.

14. The switch recovery circuit of claim 9 further comprising:

a second capacitor coupled to said second inductor at a first node; and

a third inductor coupled to both said second capacitor and said second inductor at said first node.

16. The switch recovery circuit of claim 9 further comprising a current source coupled to said switch and said first inductor.

17. A switch recovery circuit for use in conjunction with a switch and an input energy source, comprising:

a first inductor coupled between said switch and said input energy source;

a second inductor magnetically coupled to said first inductor;

a first capacitor coupled to said second inductor such that current flowing from said second inductor to said first capacitor charges said first capacitor; and

a third inductor coupled to the parallel combination of said first capacitor and said second inductor, said third inductor also coupled to said first inductor;

a first switching device coupled to said second inductor such that said first switching device is capable of preventing current from flowing from said first capacitor through said second inductor;

wherein

said first inductor is coupled to said third inductor such that current flows from said third inductor to said first inductor at least at some point in time while said switch is open.

18. The switch recovery circuit of claim 17 further comprising a current source coupled to said switch and said first inductor.

19. A switching regulator circuit having an input node, an output node, and a ground node, said circuit comprising:

a first transistor;

a second transistor;

a first inductor, wherein said first transistor, said second transistor, and said first inductor are coupled between said input node and said ground node;

a control circuit for switching said first and second transistors out of phase with each other;

a second inductor magnetically coupled to said first inductor;

a first capacitor with first and second terminals coupled between said first and second inductors such that said first terminal is associated with said first inductor and said second terminal is associated with said second inductor;

a first switching device coupled to said second inductor;

wherein

the polarity of the magnetic coupling between said first inductor and said second inductor is such that changes in voltage across said first inductor with respect to said first terminal of said capacitor correspond to the same polarity changes in voltage across said second inductor with respect to said second terminal of said capacitor;

said first inductor is coupled to said first capacitor such that current flows from said first inductor to said first capacitor at least at some point in time while said second transistor does not conduct current; and

said first switching device is capable of preventing current from flowing through said second inductor in at least one direction.

20. The switch recovery circuit of claim 19 wherein said magnetic coupling between said first and second inductors is such that the voltage across said first inductor corresponds to a greater voltage across said second inductor.

21. A method for returning energy stored in a capacitor as a result of the switching action of a switch, said method comprising the steps:

(a) passing current through a first inductor through said switch;

(b) preventing at least a portion of current flowing from said inductor to flow through said switch, thereby reducing the current through said first inductor, thereby reducing a voltage across said first inductor;

(c) after step (b), providing current from said first inductor to said capacitor so as to decrease the reduction in current caused by performing step (b), thereby increasing the voltage across said capacitor;

(d) responsive to the voltage across said first inductor reaching a threshold value, providing current through said capacitor so as to decrease the voltage across said capacitor.

22. The method of claim 21 wherein step (d) is performed at least in part by a second inductor magnetically coupled to said first inductor.

23. The method of claim 22 wherein a voltage across said first inductor corresponds to a greater voltage across said second inductor.