METHOD AND APPARATUS FOR A CONTROL CIRCUIT WITH MULTIPLE OPERATING MODES

• US 20120320634A1
• Filed: 08/27/2012
• Published: 12/20/2012
• Est. Priority Date: 10/04/2006
• Status: Active Grant

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Power Integrations Incorporated
• Inventors: Bäurle, Stefan, Pham, Giao
• Granted Patent: US 8,767,414 B2
• Time in Patent Office: Days
• US Class Current: 363/21.01
• 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 example controller for use in a power converter includes an oscillator that is to be coupled to a switch of the power converter to determine a switching cycle period of the switch. The controller also includes means for controlling a duty cycle of the switch to regulate an output of the power converter and for maintaining a substantially constant rate of change of the duty cycle with respect to changes in a magnitude of a feedback signal as the controller transitions between duty cycle control modes such that a control loop gain of the power converter is substantially constant during the transition.

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 switching cycle period of the switch; and

means for controlling a duty cycle of the switch to regulate an output of the power converter and for maintaining a substantially constant rate of change of the duty cycle with respect to changes in a magnitude of a feedback signal as the controller transitions between a first duty cycle control mode and a second duty cycle control mode such that a control loop gain of the power converter is substantially constant during the transition.

2. The controller of claim 1, wherein the first duty cycle control modes includes the oscillator generating an output signal to fix the switching cycle period of the switch and wherein the second duty cycle control modes includes the oscillator generating the output signal to vary the switching cycle period of the switch in response to the magnitude of the feedback signal.

3. The controller of claim 1, wherein the first duty cycle control modes includes the oscillator generating an output signal to fix the switching cycle period of the switch and wherein the second duty cycle control modes includes the oscillator generating the output signal to vary the switching cycle period of the switch such that the switching cycle period is proportional to a ratio of an on time of the switch to the magnitude of the feedback signal.

4. The controller of claim 1, wherein the first duty cycle control modes includes the controller maintaining a constant magnitude of a peak current flowing in the switch and wherein the second duty cycle control mode includes the controller varying the magnitude of the peak current in response to the magnitude of the feedback signal.

5. The controller of claim 1, further comprising means for controlling the duty cycle of the switch to be proportional to the magnitude of the feedback signal during the first and second duty cycle control modes and during the transition of the controller between the first and second duty cycle control modes.

6. The controller of claim 1, wherein the controller transitions from the first duty cycle control mode to the second duty cycle control mode in response to the magnitude of the feedback signal reaching a first value, and wherein the controller transitions from the second duty cycle control mode to the first duty cycle control mode in response to the magnitude of the feedback signal reaching the same first value, without hysteresis.

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 switching cycle period 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 one of the first and second duty cycle control modes.

9. The controller of claim 8, further comprising means for capturing and holding the value of the discharge current at a 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.

10. 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.