Method and apparatus for a control circuit with multiple operating modes

• US 8,000,114 B2
• Filed: 03/26/2009
• Issued: 08/16/2011
• Est. Priority Date: 10/04/2006
• Status: Active Grant

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Power Integrations Incorporated
• Inventors: Pham, Giao, Bäurle, Stefan
• Primary Examiner(s): Riley; Shawn
• Application Number:
  US12/412,122
• Publication Number:
  US 20090185396A1
• Time in Patent Office: 873 Days
• Field of Search: 363/21.13, 363/21.17, 363/131, 363/21.12
• US Class Current: 363/21.13
• 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 3/33515 with digital control

Abstract

An apparatus of regulating a power converter with multiple operating modes includes a switch coupled to an energy transfer element coupled between an input and an output of the power converter. A control circuit is also included, which is coupled to the switch to control the switch. The control circuit includes first and second duty cycle control modes to regulate power delivered to the output of the power converter. A transition between the first and second duty cycle control modes is responsive to a magnitude of a current flowing in the switch reaching a current threshold value.

Claims

1. A controller for use in a power converter, the controller comprising:

an oscillator to be coupled to a switch of the power converter to determine a time at which the switch is turned on at a beginning of a switching cycle of the switch; and

a logic circuit to be coupled to the switch to determine a time at which the switch is turned off during the switching cycle of the switch, wherein the controller includes first and second duty cycle control modes responsive to a magnitude of a feedback signal to regulate power delivered to an output of the power converter, wherein in response to the magnitude of the feedback signal being below a threshold, the oscillator generates an output signal to fix a time period of the switching cycle of the switch during the first duty cycle control mode and wherein in response to the magnitude of the feedback signal being above the threshold, the oscillator generates the output signal to vary the time period of the switching cycle of the switch during the second duty cycle control mode.

2. The controller of claim 1, wherein the controller is adapted to transition between the first and second duty cycle control modes responsive to a magnitude of current flowing in the switch reaching a current threshold value.

3. The controller of claim 1, wherein the controller maintains a constant magnitude of a peak current flowing in the switch during the second duty cycle control mode.

4. The controller of claim 1, further comprising a feedback terminal to be coupled to receive the feedback signal of the power converter, wherein an on time of the switch is directly proportional to the magnitude of the feedback signal during the first duty cycle control mode.

5. The controller of claim 1, further comprising a feedback terminal to be coupled to receive the feedback signal of the power converter, wherein the oscillator generates the output signal to vary the time period of the switching cycle in response to the magnitude of the feedback signal during the second duty cycle control mode.

6. The controller of claim 5, wherein the oscillator generates the output signal to vary the time period of the switching cycle of the switch during the second duty cycle control mode such that the time period of the switching cycle is proportional to a ratio of an on time of the switch and the magnitude of the feedback signal.

7. The controller of claim 1, wherein the oscillator further comprises:

a capacitor; and

a charging current source and a discharging current source coupled to charge and discharge the capacitor, respectively, wherein a time period for the capacitor to charge and discharge between first and second voltage levels is the time period of the switching cycle of the switch.

8. The controller of claim 7, wherein a value of discharge current of the discharging current source is varied while a value of charge current of the charging current source is fixed during the second duty cycle control mode.

9. The controller of claim 8, further comprising a sample and hold circuit coupled to the oscillator and coupled to capture and hold the value of the discharge current at the time at which the switch is turned off, wherein the value of the discharge current is varied in response to the value of the discharge current captured and held by the sample and hold circuit.

10. The controller of claim 9, wherein the switch is a first switch and wherein the logic circuit is coupled to output a gate drive signal to control the first switch, wherein the sample and hold circuit further comprises:

a capacitor to store a voltage; and

a sample and hold switch coupled to the capacitor and coupled to receive the gate drive signal to open the sample and hold switch at the time at which the first switch is turned off, wherein the voltage stored in the capacitor at the time at which the first switch is turned off is proportional to the value of the discharge current.

11. The controller of claim 1, wherein controller and the switch form part of an integrated circuit that is manufactured as a hybrid or monolithic integrated circuit.