APPARATUS AND METHOD FOR CONTROL AND DRIVING BJT USED AS SYNCHRONOUS RECTIFIER

• US 20030063484A1
• Filed: 10/03/2001
• Published: 04/03/2003
• Est. Priority Date: 10/03/2001
• Status: Active Grant

• Current Assignee: Bruce W. Carsten
• Original Assignee: Bruce W. Carsten
• Inventors: Carsten, Bruce W.
• Granted Patent: US 6,563,725 B2
• Time in Patent Office: Days
• US Class Current: 363/127
• CPC Class Codes: H02M 3/33592 having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
• 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 bipolar junction transistor (BJT) used as a synchronous rectifier (SR) that is driven and controlled by an electronic circuit, such that when the collector-emitter voltage (VCE) is above an offset voltage (VOS) the circuit drives the base of the SR BJT with a base current proportional to the difference between VCE and VOS, turning the SR BJT on with a base current proportional to the collector current. When the VCE of the SR BJT falls below VOS the drive circuit turns on a second transistor coupled between the base and collector of the SR BJT to turn the SR BJT rapidly off and maintains it in the off state as the collector voltage reverses. When the VCE of the SR BJT is exceeds a threshold voltage above the normal conduction VCE range, the control circuit increases the base drive current to accelerate the SR BJT turn-on process.

Claims

1. A control and drive circuit for a BJT rectifier, comprising:

an input adapted for coupling to a collector and an emitter of a BJT rectifier and configured to comprise a sensing pathway that senses a signal representative of the collector to emitter voltage (VCE) of that BJT rectifier;

an output adapted for coupling to a base of that BJT rectifier;

a drive circuit coupled to said input and said output that produces a base drive current (IB); and

an offset circuit coupled to said drive circuit that provides an offset of a given value (offset value);

said drive circuit being configured to produce a positive base drive current at said output that is proportional to the sensed VCE minus said offset value when the sensed VCE is essentially greater than said offset value, and to produce a negative base drive current at said output when the sensed VCE is essentially less than said offset value; and

said sensing pathway being comprised of sensing pathway components and being configured so as to substantially compensate for component induced variations in sensed VCE due to changes in operating conditions.

2. The circuit of claim 1, wherein said sensing pathway is configured such that a VCE sensed through said pathway varies approximately 1.6 mV or less per change in degree C.

3. The circuit of claim 1, wherein said sensing pathway is configured such that a VCE sensed through said pathway varies approximately 1 mV or less per change in degree C.

4. The circuit of claim 1, wherein said drive circuit is further configured to enhance production of said negative base drive current when a sensed VCE is below a first threshold.

5. The circuit of claim 4, wherein said first threshold voltage is below said offset value.

6. The circuit of claim 1, wherein said drive circuit is further configured to enhance production of said positive base drive current when a sensed VCE is above a second threshold.

7. The circuit of claim 1, wherein said offset circuit includes an offset voltage source.

8. The circuit of claim 1, wherein said offset circuit includes an offset current source.

9. The circuit of claim 1, wherein said offset circuit includes circuitry that provides at least one of the functions of:

inducing an imbalance in said sensing pathway;

or

inducing a variation in the base drive current produced by said drive circuit that approximates the effect of having an imbalance in said sensing pathway.

10. The circuit of claim 1, wherein said driving circuit is configured to produce a base drive current approximately equal to zero, when a sensed VCE is approximately equal to said offset value.

11. The circuit of claim 1, wherein said drive circuit is powered by a single supply voltage.

12. A control and drive circuit for a BJT rectifier, comprising:

an input adapted for coupling to a collector and an emitter of a BJT rectifier and configured to comprise a sensing pathway that senses a signal representative of the collector to emitter voltage (VCE) of that BJT rectifier;

an output adapted for coupling to a base of that BJT rectifier;

a drive circuit coupled to said input and output that produces a base drive current (IB); and

an offset circuit coupled to said drive circuit that provides an offset of a given value (offset value);

said drive circuit being configured to produce a positive base drive current at said output when a sensed VCE is approximately greater than said offset value, and to produce a negative base drive current at said output when the sensed VCE is approximately less than said offset value; and

said sensing pathway being configured to compensate for component induced variations in sensed VCE due to changes in operating temperature.

13. The circuit of claim 12, wherein said sensing pathway includes one or more of a semiconductor junction voltage drop and a PN junction voltage drop and said sensing pathway is configured to compensate for temperature dependent variations induced by said one or more junction voltage drops.

14. The circuit of claim 12, wherein said drive circuit is configured to produce a positive base drive current at said output that is proportional to a sensed VCE minus said offset value when the sensed VCE is approximately greater than said offset value.

15. The circuit of claim 12, wherein said sensing pathway is configured such that a VCE sensed through said pathway varies approximately 1.6 mV or less per change in degree C.

16. The circuit of claim 12, wherein said sensing pathway is configured such that a VCE sensed through said pathway varies approximately 1 mV or less per change in degree C.

17. The circuit of claim 12, wherein said drive circuit is further configured to provide at least one of enhanced production of said negative base drive current when a sensed VCE is below a first threshold or enhanced production of said positive base drive current when a sensed VCE is above a second threshold.

18. The circuit of claim 12, wherein said offset circuit includes one or more of the offset inducing components including:

an offset voltage source;

an offset current source;

or

circuitry that provides at least one of the functions of;

inducing an imbalance in said sensing pathway;

or

inducing a variation in the base drive current produced by said drive circuit that approximates the effect of having an imbalance in said sensing pathway.

19. The circuit of claim 12, wherein said driving circuit is configured to produce a base drive current approximately equal to zero, when a sensed VCE is approximately equal to said offset value.

20. The circuit of claim 12, wherein said drive circuit is powered by a single supply voltage.

21. A control and drive circuit for a BJT rectifier, comprising:

an input adapted for coupling to a collector and an emitter of a BJT rectifier and configured to comprise a sensing pathway that senses a signal representative of the collector to emitter voltage (VCE) of that BJT rectifier;

an output adapted for coupling to a base of that BJT rectifier;

a drive circuit coupled to said input and output that produces a base drive current (IB); and

an offset circuit coupled to said drive circuit that provides an offset of a given value (offset value);

said drive circuit being configured to produce a positive base drive current at said output that is proportional to a sensed VCE minus said offset value when the sensed VCE is approximately greater than said offset value, and to produce a negative base drive current at said output when the sensed VCE is approximately less than said offset value.

22. The circuit of claim 21, wherein said sensing pathway includes one or more of a semiconductor junction voltage drop and a PN junction voltage drop and said sensing pathway is configured to compensate for temperature dependent variations induced by said one or more junction voltage drops.

23. The circuit of claim 21, wherein said sensing pathway is configured such that a VCE sensed through said pathway varies approximately 1.6 mV or less per change in degree C.

24. The circuit of claim 21, wherein said sensing pathway is configured such that a VCE sensed through said pathway varies approximately 1 mV or less per change in degree C.

25. The circuit of claim 21, wherein said drive circuit is further configured to provide at least one of enhanced production of said negative base drive current when a sensed VCE is below a first threshold and enhanced production of said positive base drive current when a sensed VCE is above a second threshold.

26. The circuit of claim 21, wherein said drive circuit is powered by a single supply voltage.