METHOD AND APPARATUS FOR MAINTAINING A CONSTANT LOAD CURRENT WITH LINE VOLTAGE IN A SWITCH MODE POWER SUPPLY

• US 20110025288A1
• Filed: 10/13/2010
• Published: 02/03/2011
• Est. Priority Date: 09/27/2001
• Status: Active Grant

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Power Integrations Incorporated
• Inventors: Wong, Kent, Matthews, David Michael Hugh, Balakrishnan, Balu, Djenguerian, Alex B.
• Granted Patent: US 8,013,584 B2
• Time in Patent Office: Days
• US Class Current: 323/284
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• 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
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop
• CPC Class Codes: H03K 17/0822 in field-effect transistor switches

Abstract

A power supply regulator including a variable current limit threshold that increases during an on time of a switch. In one aspect, a power supply regulator includes a comparator coupled to receive a signal representative of a current through a switch during an on time of the switch. The comparator is further coupled to receive a variable current limit threshold that increases during the on time of the switch. The power supply regulator also includes a feedback circuit coupled to receive a feedback signal representative of an output of a power supply. A control circuit is also included and is coupled to the switch, to an output of the comparator, and to an output of the feedback circuit. The control circuit is coupled to control a switching of the switch in response the output of the comparator and the output of the feedback circuit to regulate the output of the power supply.

Claims

1. A power supply regulator, comprising:

a comparator coupled to receive a signal representative of a current through a switch during an on time of the switch, the comparator further coupled to receive a variable current limit threshold that increases during the on time of the switch;

a feedback circuit coupled to receive a feedback signal representative of an output of a power supply; and

a control circuit coupled to the switch, to an output of the comparator, and to an output of the feedback circuit, the control circuit coupled to control a switching of the switch in response the output of the comparator and the output of the feedback circuit to regulate the output of the power supply.

2. The power supply regulator of claim 1 further comprising an oscillator coupled to generate a sawtooth waveform, wherein the variable current limit threshold is generated in response to the sawtooth waveform.

3. The power supply regulator of claim 2 wherein the feedback circuit is further coupled to the oscillator, wherein the feedback circuit is responsive to the output of the power supply and the sawtooth waveform.

4. The power supply regulator of claim 2 wherein the oscillator is further coupled to generate a maximum duty cycle signal coupled to be received by the control circuit, wherein the control circuit is coupled to control the switching of the switch further in response to the maximum duty cycle signal.

5. The power supply regulator of claim 2 wherein the control circuit further comprises a latch coupled to control the switching of the switch, wherein the latch includes a first input coupled to be responsive to the output of the comparator.

6. The power supply regulator of claim 5 wherein the latch further includes a second input coupled to be responsive to a clock signal generated by the oscillator.

7. The power supply regulator of claim 5 wherein the first input of the latch is further coupled to be responsive to a maximum duty cycle signal generated by the oscillator.

8. The power supply regulator of claim 5 wherein the feedback circuit includes a feedback comparator coupled to receive the feedback signal and to receive the sawtooth waveform, wherein the first input of the latch is further coupled to be responsive to the output of the feedback comparator.

9. The power supply regulator of claim 1 wherein a duty cycle of a control signal generated by the control circuit to control the switching of the switch is coupled to be modulated in response to the feedback circuit.

10. The power supply regulator of claim 2 further comprising a current mirror coupled to the comparator and to the oscillator, the current minor coupled to generate the variable current limit threshold in response to the sawtooth waveform.