Method and apparatus for maintaining an approximate constant current output characteristic in a switched mode power supply

• US 20030132738A1
• Filed: 01/16/2003
• Published: 07/17/2003
• Est. Priority Date: 01/17/2002
• Status: Active Grant

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Power Integrations Incorporated
• Inventors: Wong, Kent, Balakrishnan, Balu, Bircan, Erdem, Djenguerian, Alex B., Hugh Matthews, David Michael
• Granted Patent: US 6,833,692 B2
• Time in Patent Office: Days
• US Class Current: 323/282
• CPC Class Codes: H02M 1/0006 Arrangements for supplying an adequate voltage to the control circuit of converters
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence

Abstract

A regulator circuit maintaining an approximate constant current output characteristic. In one aspect, a disclosed regulator controls a switch that has a current limit threshold. A supply terminal and feedback terminal of the regulator are connected together as a control terminal such that a shunt regulator current is the control terminal current in excess of the internal supply current consumed by the regulator. The current limit threshold of the switch is changed as a function of the shunt regulator current. In another aspect, a control input of the regulator circuit receives a current that is the sum of the internal supply current consumed by the regulator circuit and a feedback current. The feedback current is a fraction of the consumption current of the regulator circuit and the current limit threshold of the switch is changed as a function of the feedback current.

Claims

1. A regulator, comprising:

a switch having a current limit threshold, the switch coupled between first and second terminals;

a control circuit coupled to the switch to control a current through the switch in response to the current limit threshold; and

a control terminal regulator circuit coupled to the control circuit and to a control terminal of the regulator, the control terminal coupled to receive a control terminal current including an internal supply current, the regulator circuit including a shunt regulator coupled to the control terminal to derive a shunt regulator current from the control terminal current, wherein the shunt regulator current is the control terminal current in excess of the internal supply current, wherein the current limit threshold is increased in response to an increase in the shunt regulator current.

2. The regulator of claim 1 wherein the control terminal comprises a combined feedback terminal and supply terminal of the regulator, wherein the feedback terminal and supply terminal are internally connected in the regulator.

3. The regulator of claim 1 wherein the control terminal comprises a combined feedback terminal and supply terminal of the regulator, wherein the feedback terminal and supply terminal are externally connected.

4. The regulator of claim 1 wherein the regulator is included in a monolithic chip.

5. The regulator of claim 1 wherein the power switch comprises a metal oxide semiconductor field effect transistor (MOSFET).

6. The regulator of claim 1 wherein the power switch comprises a bipolar junction transistor.

7. The regulator of claim 1 wherein the regulator is included in a switching power supply.

8. The regulator of claim 1 wherein the regulator is included in a switching power supply with an approximately constant output voltage and output current characteristic.

9. A regulator, comprising:

a switch having a current limit threshold, the switch coupled between first and second terminals;

a control circuit coupled to the switch to control a current through the switch in response to the current limit threshold; and

a control terminal regulator circuit coupled to the control circuit and to a control terminal of the regulator, the control terminal coupled to receive a control terminal current including an internal supply current and a feedback current, wherein the current limit threshold is increased in response to an increase in the feedback current.

10. The regulator of claim 9 wherein the regulator is included in a monolithic chip.

11. The regulator of claim 9 wherein the power switch comprises a metal oxide semiconductor field effect transistor (MOSFET).

12. The regulator of claim 9 wherein the power switch comprises a bipolar junction transistor.

13. The regulator of claim 9 wherein the regulator is included in a switching power supply.

14. The regulator of claim 9 wherein the regulator is included in a switching power supply with an approximately constant output voltage and output current characteristic.

15. A method of regulating the level at a power supply output, comprising:

receiving a control terminal current, the control terminal current including a feedback current and an internal supply current;

enabling and disabling a current to flow through a power switch in response to a current limit threshold of the power switch; and

adjusting the current limit threshold of the power switch in response to the feedback current to maintain an approximately constant output current characteristic of the power supply.

16. The method of claim 15 further comprising determining the control terminal current in excess of the internal supply current to determine the feedback current.

17. The method of claim 15 further comprising increasing the current limit threshold in response to an increase in the feedback current.

18. The method of claim 15 further comprising decreasing the current limit threshold in response to an increase in the feedback current.

19. The method of claim 15 further comprising maintaining an approximately constant output voltage in response to the feedback current.

20. A power supply regulator, comprising:

a power switch coupled between first and second terminals;

a control circuit coupled to control the power switch; and

a control terminal regulator circuit coupled to the control circuit and a control terminal to receive a control terminal current, the control terminal current including an internal supply current for the power supply regulator, the control terminal current further including a feedback current, wherein a current limit threshold of the power switch is adjusted in response to the feedback current, wherein the control circuit is adapted to control the power switch in response to the feedback current to provide an approximately constant output voltage and output current characteristic in the power supply.

21. The power supply regulator of claim 20 further comprising a charging circuit coupled to the control terminal regulator circuit, the first terminal and the control terminal, adapted to maintain the control terminal at a predetermined constant voltage level.

22. The power supply regulator of claim 20 further comprising a current limit adjust circuit coupled to the control terminal, the control terminal regulator circuit and the control circuit, the current limit adjust circuit adapted to adjust the current limit threshold in response to the feedback signal.

23. The power supply regulator of claim 20 wherein the current limit threshold is increased with increasing feedback current

24. The power supply regulator of claim 20 wherein the current limit threshold is decreased with increasing feedback current

25. The power supply regulator of claim 20 wherein the control terminal regulator circuit includes a shunt regulator coupled to the control terminal, wherein a shunt regulator current is adapted to flow through the shunt regulator, wherein the shunt regulator current is the control terminal current in excess of the internal supply current.

26. The power supply regulator of claim 20 wherein the power switch includes a metal oxide semiconductor field effect transistor (MOSFET), wherein the first terminal is a drain terminal and the second terminal is a source terminal.

27. The power supply regulator of claim 20 wherein the power switch includes a bipolar junction transistor.