Controller for switching power converter driving BJT based on primary side adaptive digital control

• US 8,289,732 B2
• Filed: 12/16/2009
• Issued: 10/16/2012
• Est. Priority Date: 12/23/2008
• Status: Active Grant

• Current Assignee: Dialog Semiconductor Incorporated (Renesas Electronics Corporation)
• Original Assignee: iWatt, Inc. (Renesas Electronics Corporation)
• Inventors: Li, Yong, Zheng, Jun, Zheng, Junjie, Kesterson, John William
• Primary Examiner(s): Berhane, Adolf
• Assistant Examiner(s): PHAM, EMILY P
• Application Number:
  US12/639,399
• Publication Number:
  US 20100157636A1
• Time in Patent Office: 1,035 Days
• Field of Search: 363/20, 363/21.01, 363/21.04, 363/21.08, 363/21.12, 363/21.16, 363/124
• US Class Current: 363/21.12
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 3/33515 with digital control

Abstract

A controller of an AC/DC flyback switching power supply uses adaptive digital control approaches to control the switching operation of a BJT power switch based on primary-side feedback to regulate the secondary-side constant output voltage and output current, without using the input line voltage. Switching-cycle by switching-cycle peak current control and limit are achieved based on the sensed primary-side current rather than the input line voltage in both constant-voltage and constant-current modes, operating in PWM, PFM and/or combinations of a plurality of PWM and PFM modes. The controller IC does not need a separate pin and ADC circuitry for sensing the input line voltage. The controller IC directly drives the BJT base, and dynamically adjusts the BJT base current amplitude cycle by cycle based on load change.

Claims

1. A switching power converter comprising:

a transformer coupled between an input voltage and an output of the switching power converter, the transformer including a primary winding coupled to the input voltage and a secondary winding coupled to the output of the switching power converter;

a switch coupled to the primary winding of the transformer, current through the primary winding being generated while the switch is turned on and not being generated while the switch is turned off; and

a controller configured to generate a control signal to turn on or turn off the switch, the switch being turned on responsive to the control signal being in a first state and the switch being turned off responsive to the control signal being in a second state,

wherein the controller is further configured to generate the control signal in the second state to turn off the switch responsive to a sensed signal indicative of the current through the primary winding exceeding a peak current threshold for peak current switching of the switching power converter, wherein a slope of increase of the sensed signal indicative of the current through the primary winding is substantially proportional to the input voltage to the switching power converter and is a proxy for the input voltage.

2. The switching power converter of claim 1, wherein the controller does not receive or use a level of the input voltage in regulation of output voltage or output current of the switching power converter.

3. The switching power converter of claim 1, wherein the controller is an integrated circuit chip that does not include a separate pin for receiving the input voltage of the switching power converter during normal operation of the switching power converter.

4. The switching power converter of claim 1, wherein the controller is an integrated circuit chip with five pins, the five pins including a first pin for receiving a supply voltage for the controller, a second pin for connection to ground, a third pin for receiving a voltage signal indicative of a scaled down output voltage of the switching power converter, a fourth pin for receiving the sensed signal indicative of current in the primary winding, and a fifth pin for outputting the control signal to turn on or turn off the switch.

5. The switching power converter of claim 1, wherein the sensed signal is a voltage measured across a resistor through which the current in the primary winding flows.

6. The switching power converter of claim 1, wherein the switch is a bipolar junction transistor, the control signal directly drives a base terminal of the bipolar junction transistor to provide a base current in the bipolar junction transistor, and the controller dynamically adjusts an amplitude of the base current switching-cycle by switching-cycle based on change in a load of the switching power converter.

7. The switching power converter of claim 1, wherein the controller includes a peak current comparator for comparing the sensed signal with the peak current threshold.

8. The switching power converter of claim 1, wherein the controller is further configured to generate the control signal in the second state to turn off the switch responsive to the sensed signal indicative of current in the primary winding of the transformer exceeding a predetermined voltage indicative of an over-current condition.

9. The switching power converter of claim 1, wherein the switching power converter does not include an analog-to-digital converter for converting the input voltage to a digital value for use by the controller in regulation of output voltage or output current of the switching power converter.

10. The switching power converter of claim 1, wherein the switching power converter is a primary-side feedback, flyback-type switching power converter.

11. A switching power converter comprising:

a transformer coupled between an input voltage and an output of the switching power converter, the transformer including a primary winding coupled to the input voltage and a secondary winding coupled to the output of the switching power converter;

a switch coupled to the primary winding of the transformer, current through the primary winding being generated while the switch is turned on and not being generated while the switch is turned off; and

a controller configured to generate a control signal to turn on or turn off the switch, the switch being turned on responsive to the control signal being in a first state and the switch being turned off responsive to the control signal being in a second state,

wherein the controller does not receive the input voltage for regulation of output voltage or output current of the switching power converter and uses a slope of increase of a sensed signal indicative of the current through the primary winding as a proxy for the input voltage.

12. The switching power converter of claim 11, wherein the controller is an integrated circuit chip that does not include a separate pin for receiving the input voltage of the switching power converter during normal operation of the switching power converter.

13. The switching power converter of claim 11, wherein the controller is an integrated circuit chip with five pins, the five pins including a first pin for receiving a supply voltage for the controller, a second pin for connection to ground, a third pin for receiving a voltage signal indicative of a scaled down output voltage of the switching power converter, a fourth pin for receiving the sensed signal indicative of current in the primary winding, and a fifth pin for outputting the control signal to turn on or turn off the switch.

14. The switching power converter of claim 11, wherein the switch is a bipolar junction transistor, the control signal directly drives a base terminal of the bipolar junction transistor to provide a base current in the bipolar junction transistor, and the controller dynamically adjusts an amplitude of the base current switching-cycle by switching-cycle based on change in a load of the switching power converter.

15. The switching power converter of claim 11, wherein the switching power converter does not include an analog-to-digital converter for converting the input voltage to a digital value for use by the controller for regulation of the output voltage or the output current of the switching power converter.

16. The switching power converter of claim 11, wherein the switching power converter is a primary-side feedback, flyback-type switching power converter.

17. In a controller, a method of controlling a switching power converter, the switching power converter including a transformer coupled between an input voltage and an output of the switching power converter, the transformer including a primary winding coupled to the input voltage and a secondary winding coupled to the output of the switching power converter, and a switch coupled to the primary winding of the transformer, current through the primary winding being generated while the switch is turned on and not being generated while the switch is turned off, the method comprising:

generating a control signal to turn on the switch, the switch being turned on responsive to the control signal being in a first state; and

generating the control signal in a second state to turn off the switch, responsive to a sensed signal indicative of the current in the primary winding of the transformer exceeding a peak current threshold for peak current switching of the switching power converter, wherein a slope of increase of the sensed signal indicative of the current through the primary winding is substantially proportional to the input voltage to the switching power converter and is a proxy for the input voltage.

18. The method of claim 17, wherein a level of the input voltage is not received or used by the controller for regulation of output voltage or output current of the switching power converter.

19. The method of claim 17, wherein the sensed signal is a voltage measured across a resistor through which the current in the primary winding of the transformer flows.

20. The method of claim 17, further comprising generating the control signal in a second state to turn off the switch, responsive to a sensed signal indicative of current in the primary winding of the transformer exceeding a predetermined voltage indicative of an over-current condition.

21. The method of claim 17, wherein a slope of increase of the sensed signal indicative of the current in the primary winding is substantially proportional to the input voltage to the switching power converter.

22. The method of claim 17, wherein the switch is a bipolar junction transistor, the control signal directly drives a base terminal of the bipolar junction transistor to provide a base current in the bipolar junction transistor, and the controller dynamically adjusts an amplitude of the base current switching-cycle by switching-cycle based on change in a load of the switching power converter.

23. The method of claim 17, wherein the switching power converter is a primary-side feedback, flyback-type switching power converter.