Primary-side-control power converter having a switching controller using frequency hopping and voltage and current control loops

• US 20060077697A1
• Filed: 10/07/2004
• Published: 04/13/2006
• Est. Priority Date: 10/07/2004
• Status: Active Grant

• Current Assignee: Fairchild Semiconductor Corporation (ON Semiconductor Corporation)
• Original Assignee: System General Corporation (ON Semiconductor Corporation)
• Inventors: Yang, Ta-yung
• Granted Patent: US 7,259,972 B2
• Time in Patent Office: Days
• US Class Current: 363/21.130
• CPC Class Codes: H02M 1/44 Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
• 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 power converter includes a switch and a controller. The switch switches electrical power in the power converter. The controller generates a switching signal to control the switch in response to a first feedback signal associated with a voltage control loop and a second feedback signal associated with a current control loop. The controller can also allow the switching frequency to hop from frequency to frequency according to a digital pattern.

Claims

1. A power converter comprising:

a switch, responsive to a switching signal, to control electrical power in the power converter; and

a controller to generate the switching signal and to control the switching signal in response to a first feedback signal associated with a voltage control loop and a second feedback signal associated with a current control loop.

2. The power converter of claim 1, wherein the controller generates a frequency-hopping switching signal to the switch.

3. The power converter of claim 2, wherein the controller generates a digital pattern for the frequency-hopping switching signal.

4. The power converter of claim 1, further comprising:

a transformer to transfer electrical power from a primary-side of the power converter to a secondary-side of the power converter, and wherein the switch is to switch the transformer.

5. The power converter of claim 4, wherein the transformer includes an auxiliary winding, a primary winding, and a secondary winding, and wherein the switch controls electrical power flowing through at least the primary winding.

6. The power converter of claim 5, wherein the controller generates the first feedback signal by sampling a voltage from the auxiliary winding of the transformer and a discharge time of the transformer.

7. The power converter of claim 6, further comprising:

a sense circuit to sense current through the primary winding of the transformer.

8. The power converter of claim 7, wherein the controller generates the second feedback signal by sampling of the sensed current from the sense circuit and the discharge time of the transformer.

9. The power converter of claim 8, wherein the discharge time of the transformer occurs while the switching signal is off.

10. The power converter of claim 4, wherein the current control loop limits the peak current flowing through the transformer.

11. The power converter of claim 10, wherein the current control loop controls an average value of a secondary-side current in the power converter.

12. The power converter of claim 5, wherein the voltage control loop limits the peak auxiliary voltage associated with the auxiliary winding.

13. A method for regulating power in a power converter, comprising:

receiving electrical power from input terminals; and

controlling a switching signal to regulate the connection of the electrical power to output terminals in response to a first feedback signal associated with a voltage control loop and a second feedback signal associated with a current control loop.

14. The method of claim 13, further comprising:

generating a frequency-hopping switching signal in order to reduce at least electro-magnetic interference (EMI).

15. The method of claim 14, further comprising:

generating a digital pattern for the frequency-hopping switching signal.

16. The method of claim 15, further comprising:

programming the digital pattern.

17. The method of claim 14, further comprising:

passing electrical power from a primary-side to a secondary-side of a transformer based on the switching signal.

18. The method of claim 17, further comprising:

generating the first feedback signal by sampling a voltage from an auxiliary winding of the transformer and a discharge time of the transformer.

19. The method of claim 18, further comprising:

sensing a current through a primary winding of the transformer.

20. The method of claim 19, further comprising:

generating the second feedback signal by sampling of sensed current and the discharge time of the transformer.

21. The method of claim 20, wherein the discharge time of the transformer occurs when the switching signal is off.

22. A power converter comprising:

input terminals and output terminals;

a transformer to transfer electrical power from the input terminals to the output terminals;

a switch to control the transformer in response to a switching signal having a switching frequency; and

a controller to generate the switching signal and to allow the switching frequency to hop from frequency to frequency according to a digital pattern.

23. The power converter of claim 22, wherein the controller adjusts the digital pattern.

24. The power converter of claim 22, wherein the controller generates the switching signal in response to a first feedback signal associated with a voltage control loop and a second feedback signal associated with a current control loop.

25. A power converter comprising:

input terminals and output terminals;

a transformer to transfer electrical power from the input terminals to the output terminals;

a switch to switch the transformer in response to a switching signal having a switching frequency; and

a controller to generate the switching signal in response to a first feedback signal associated with a voltage control loop and a second feedback signal associated with a current control loop in the primary-side of the transformer.

26. The power converter of claim 25, wherein the voltage control loop provides voltage-loop frequency compensation and the current control loop provides current-loop frequency compensation.

27. The power converter of claim 25, wherein the controller comprises:

a first waveform detector to generate the first feedback signal and a discharge-time signal of the transformer;

a second waveform detector and an integrator to generate the second feedback signal;

a first error amplifier and a second error amplifier for amplifying the first feedback signal and the second feedback signal, respectively;

an oscillator to generate a pulse signal and a timing signal in response to an output of the second error amplifier;

a peak-current limiter to limit a sensed current signal; and

a PWM circuit to generate the switching signal in response to the pulse signal, an output of the first error amplifier, and an output of the peak-current limiter.

28. The power converter of claim 27, wherein the first waveform detector generates the first feedback signal by sampling a voltage signal from an auxiliary winding of the transformer, and generates the discharge-time signal using a discharge-time of a secondary-side switching current of the transformer.

29. The power converter of claim 28, wherein the integrator integrates an average-current signal with the discharge-time signal.

30. The power converter of claim 29, wherein the average-current signal is derived from a current-waveform signal integrated with the pulse width of the timing signal.

31. The power converter of claim 30, wherein the pulse width of the timing signal correlates with the switching frequency of the switching signal.

32. The power converter of claim 27, wherein the controller further comprises:

a programmable current source to provide temperature compensation and to generate a programmable current in response to a temperature of the controller.

33. The power converter of claim 32, wherein the controller further comprises:

a pattern generator to generate a digital pattern;

a first programmable capacitor coupled to the oscillator and the pattern generator for modulating the switching frequency in response to the digital pattern; and

a second programmable capacitor coupled to the integrator and the pattern generator for correlating the time constant of the integrator with the switching frequency;

wherein the capacitances of the first programmable capacitor and the second programmable capacitor are controlled by the digital pattern.

34. The power converter of claim 33, wherein the time constant of the integrator correlates with a switching period of the switching signal.

35. A power converter comprising:

a transformer coupled to an input voltage for the power converter;

a switch to switch electrical power flowing through the transformer;

a sense device coupled to the transformer to sense at least current from the transformer; and

a controller coupled to the transformer, the controller to provide a switching signal to the switch for regulating output power for the power converter, and to control the switching signal based on a first feedback signal associated with a first control loop and a second feedback signal associated with a second control loop in the primary-side of the power converter.

36. The power converter of claim 35, wherein the first control loop includes a voltage control loop and the second control loop includes a current control loop.

37. The power converter of claim 35, wherein the controller generates the first feedback signal and a discharge-time signal by sampling of a voltage associated with the transformer and a discharge-time of the transformer during an off time the switching signal.

38. The power converter of claim 37, wherein the controller generates the second feedback signal in response to the discharge-time signal and sensed current from the sense device, and controls the switching frequency of the switching signal in response to the second feedback signal.

39. The power converter of claim 35, wherein the controller comprises:

a first waveform detector coupled to the transformer, the first waveform detector to generate the first feedback signal and the discharge-time signal by sampling of a voltage signal from an auxiliary winding of the transformer, wherein the discharge time signal corresponds to the discharge time of the secondary-side switching current of the transformer;

a second waveform detector and an integrator, the second waveform detector and integrator to generate the second feedback signal by integrating an average-current signal with the discharge-time signal;

a first error amplifier and a second error amplifier to amplify the first feedback signal and the second feedback signal, respectively;

an oscillator coupled to the second error amplifier to generate a pulse signal and the timing signal in response to an output of the second error amplifier;

a peak-current limiter coupled to the sense device to limit a maximum value of the current signal;

a PWM circuit to generate the switching signal in response to the pulse signal, an output of the first error amplifier, and an output of the peak-current limiter.

40. The power converter of claim 39, wherein the second waveform detector generates the average-current signal by integrating a current-waveform signal with the pulse width of the timing signal, wherein the current-waveform signal is a measured current signal.

41. The power converter of claim 39, wherein the pulse signal determines the switching frequency of the switching signal.

42. The power converter of claim 41, wherein the controller further comprises:

a programmable current source coupled to an input of the first waveform detector for temperature compensation, and wherein the programmable current source is generate a programmable current in response to a temperature of the controller.

43. The power converter of claim 42, wherein the controller further comprises:

a pattern generator to generate a digital pattern;

a first programmable capacitor coupled to the oscillator and the pattern generator for modulating the switching frequency in accordance with the digital pattern;

a second programmable capacitor coupled to the integrator and the pattern generator to correlate a time constant of the integrator with the switching frequency, and wherein the capacitances of the first programmable capacitor and the second programmable capacitor are dictated by the digital pattern.

44. The power converter of claim 43, wherein the time constant of the integrator correlates with the switching period of the switching signal.

45. The power converter of claim 39, wherein the first waveform detector comprises:

a sample-pulse generator to generate a sample-pulse signal;

a threshold generator to generate a threshold signal that adds to the voltage signal to produce a level-shift signal;

a first capacitor and a second capacitor to provide a first-hold voltage and a second-hold voltage;

a first signal generator to generate a first sample signal and a second sample signal, wherein the first sample signal and the second sample signal are used for alternately sampling the voltage signal;

a buffer amplifier to generate a hold signal from a higher voltage of the first-hold voltage and said second-hold voltage;

a first output capacitor to generate the first feedback signal by sampling the hold signal; and

a second signal generator to generate the discharge-time signal.

46. The power converter of claim 45, wherein the first signal generator alternately generates the first sample signal and the second sample signal in response to the sample-pulse signal during an enable period of the discharge-time signal.

47. The power converter of claim 46, wherein the first signal generator inserts a delay time at a beginning of the discharge-time signal and wherein the first sample signal and second sample signal are disabled during the period of the delay time.

48. The power converter of claim 45, wherein the second signal generator generates the discharge-time signal such that it is enabled as the switching signal is disabled, and wherein after the delay time the discharge-time signal is disabled once the level-shift signal is lower than the first feedback signal, and wherein the discharge-time signal is disabled as long as the switching signal is enabled.

49. The power converter of claim 48, wherein the first waveform detector samples the voltage signal to generate an end voltage used for the first feedback signal, and wherein the end voltage is sampled and measured instantly before the secondary-side switching current falls to zero.

50. The power converter of claim 43, wherein the pattern generator comprises:

a clock generator to generate a clock signal; and

a register to generate the digital pattern in response to the clock signal.

51. The power converter of claim 39, wherein the oscillator comprises:

a first V-to-I converter to generate a first charge current, a discharge current, and a second charge current in accordance with an output of the second error amplifier, and wherein the first V-to-I converter includes a first operational amplifier, a first oscillator resistor, and a first group of transistors;

a first oscillator capacitor;

a first switch having a first terminal supplying the said first charge current and a second terminal coupled to the first oscillator capacitor;

a second switch having a first terminal coupled to the first oscillator capacitor and a second terminal driving the discharge current;

a first comparator having a non-inverting input coupled to the first oscillator capacitor, and wherein the first comparator generates the pulse signal;

a third switch having a first terminal supplying a high-threshold voltage and a second terminal coupled to an inverting input of the first comparator;

a fourth switch having a first terminal supplying a low-threshold voltage and a second terminal coupled to the inverting input of the first comparator;

an inverter having an input coupled to an output of the first comparator for producing an inverse pulse signal and wherein the pulse signal turns on/off of the second switch and the fourth switch, and wherein the inverse pulse signal turns on/off the first switch and the third switch;

a third resistor to generate a trip-point voltage in response to the second charge current;

a second oscillator capacitor;

a fifth switch connected in parallel with the second oscillator capacitor; and

a second comparator having an inverting input coupled to the second oscillator capacitor and a non-inverting input coupled to the trip-point voltage, and wherein the second comparator generates the timing signal.

52. The power converter of claim 39, wherein the second waveform detector comprises:

a peak detector to generate a peak-current signal by measuring a peak value of the current signal;

a third capacitor to hold the peak-current signal;

a second output capacitor to produce the current-waveform; and

a switch to conduct the peak-current signal to the second output capacitor.

53. The power converter of claim 39, wherein said integrator comprises:

a first V-to-I converter including a first operational amplifier, a first timing resistor, and a first group of transistors, wherein the first V-to-I converter generates a first int-charge current in response to said current-waveform signal;

a first timing capacitor to produce a first integrated signal;

a first switch having a first terminal supplying the first int-charge current and a second terminal coupled to the first timing capacitor, and wherein the timing signal controls the on/off of the first switch;

a second switch connected in parallel with the first timing capacitor for discharging the first timing capacitor;

a third switch;

a second output capacitor to produce an average-current signal by sampling the first integrated signal through the third switch;

a second V-to-I converter including a second operational amplifier, a second timing resistor, and a second group of transistors, and wherein the second V-to-I converter generates a second int-charge current in response to the average-current signal;

a third timing capacitor to produce a second integrated signal;

a fourth switch having a first terminal supplying the second int-charge current and a second terminal coupled to the third timing capacitor, and wherein said discharge-time signal controls the on/off of the fourth switch;

a fifth switch connected in parallel with the third timing capacitor for discharging the third timing capacitor;

a sixth switch; and

a fourth output capacitor to produce the second feedback signal by sampling the second integrated signal through the sixth switch.

54. The power converter of claim 35, wherein the switching signal has a minimum on-time once the switching signal is enabled in order to ensure a minimum value of the discharge-time for sampling the voltage signal.

55. A power converter comprising:

a transformer to transfer electrical power from a primary-side of the power converter to a secondary-side of the power converter;

a switch to switch the electrical power transferred by the transformer, the switching being controlled by a switching signal;

a controller to generate the switching signal and to control the switching signal in response to a first feedback signal by sampling a voltage signal and a discharge-time associated with the transformer during an off time of the switching signal.