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

• US 7,301,319 B2
• Filed: 10/17/2006
• Issued: 11/27/2007
• Est. Priority Date: 01/17/2002
• Status: Expired due to Fees

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Power Integrations Incorporated
• Inventors: Wong, Kent, Matthews, David Michael Hugh, Balakrishnan, Balu, Bircan, Erdem, Djenguerian, Alex B.
• Primary Examiner(s): STERRETT, JEFFREY L
• Application Number:
  US11/582,628
• Publication Number:
  US 20070035285A1
• Time in Patent Office: 406 Days
• Field of Search: 323/282, 323/284, 363/21.01, 363/21.04, 363/21.12, 363/97
• US Class Current: 323/284
• 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 method of regulating a level at a power supply output, comprising:

receiving a control terminal current from a control terminal of a regulator circuit, the control terminal current including a feedback current and an internal supply current;

deriving 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; and

determining at least one of a first mode and a second mode of operation in response to a level of the control terminal current to maintain an approximate constant output current characteristic of the power supply.

2. The method of claim 1 further comprising adjusting a current limit threshold of a power switch in response to the shunt regulator current according to the first mode of operation.

3. The method of claim 2 wherein adjusting the current limit threshold of the power switch comprises increasing the current limit threshold of the power switch in response to an increase in the shunt regulator current.

4. The method of claim 2 wherein adjusting the current limit threshold of the power switch includes decreasing the current limit threshold of the power switch in response to an increase in the shunt regulator current.

5. The method of claim 2 wherein adjusting the current limit threshold of the power switch includes adjusting the current limit threshold with a current limit adjust circuit.

6. The method of claim 1 further comprising adjusting the duty cycle of a power switch controlled by the regulator circuit according to the second mode of operation.

7. The method of claim 6 wherein adjusting the duty cycle of the power switch controlled by the regulator circuit comprises reducing the duty cycle when the control terminal current is high relative to a control terminal current threshold.

8. The method of claim 6 wherein adjusting the duty cycle of the power switch comprises adjusting the duty cycle of the power switch based on the shunt regulator current in excess of a threshold to maintain an approximate constant output voltage of the power supply.

9. The method of claim 8 wherein adjusting the duty cycle of the power switch comprises converting the shunt regulator current to a voltage level across a resistor to modulate the duty cycle.

10. The method of claim 1 further comprising maintaining the approximate constant output current characteristic of the power supply in response to switching on and off a power switch according to the first or second mode of operation.

11. The method of claim 1 further comprising adapting a charging circuit coupled to the control terminal to maintain the control terminal at a substantially constant voltage.