Switching power supply system, and associated control circuit to eliminate flicker of led

Patent metadata

Field	Value
Publication number	US-2016190941-A1
Application number	US-201514971994-A
Country	US
Kind code	A1
Filing date	Dec 16, 2015
Priority date	Dec 25, 2014
Publication date	Jun 30, 2016
Grant date	—

Abstract

A switching power supply system has a switching circuit and a control circuit. The control circuit has an integrating circuit providing a charge signal by integrating an output current feedback signal, a charge control circuit, and a switching control circuit controlling the switching circuit based on the charge signal and a charge reference signal. The switching power supply system controls an output current stable via controlling the charge signal, so as to eliminate flicker and shimmer of a LED load with low power loss and simple circuit.

First claim

I/We claim:

1 . A control circuit for a switching power supply system, the switching power supply system comprises a switching circuit having an input voltage, an input current and an output current, the control circuit comprising:
an integrating circuit, configured to receive an output current feedback signal representative of the output current, and configured to provide a charge signal by integrating the output current feedback signal; a charge control circuit, having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is configured to receive the charge signal, and the second input terminal is configured to receive a charge reference signal; and a switching control circuit, having an input terminal and an output terminal, wherein the input terminal is coupled to the output terminal of the charge control circuit, and the output terminal is configured to provide a switching control signal to control the switching circuit based on the charge signal and the charge reference signal.

2 . The control circuit of claim 1 , wherein the charge control circuit further comprises:
a gain control circuit, having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is configured to receive the charge signal, the second input terminal is configured to receive the charge reference signal, and the output terminal is configured to provide a gain modulation signal based on the charge signal and the charge reference signal; and a multiplying circuit, having an input terminal, a control terminal and an output terminal, wherein the input terminal is configured to receive the input voltage, the control terminal is coupled to the output terminal of the gain control circuit, and the output terminal is coupled to the input terminal of the switching control circuit to provide a modulated input voltage signal based on the gain modulation signal and the input voltage, wherein the gain modulation signal is configured to control a gain of the input voltage.

3 . The control circuit of claim 2 , further comprises a current feedback circuit, configured to sense the input current and provide an input current feedback signal, the control circuit is configured to control the switching circuit based on the input current feedback signal and the modulated input voltage signal, wherein when the input current feedback signal is larger than the modulated input voltage signal, the switching circuit is turned OFF.

4 . The control circuit of claim 1 , wherein the charge control circuit further comprises:
a charge reference signal generator, configured to provide the charge reference signal; a charge comparison circuit, configured to receive the charge signal and the charge reference signal, and configured to provide a charge comparison signal via comparing the charge signal with the charge reference signal; a gain modulation circuit, having an input terminal and an output terminal, wherein the input terminal is configured to receive the charge comparison signal; a multiplying circuit, having an input terminal, a control terminal and an output terminal, wherein the input terminal is configured to receive the input voltage, the control terminal is coupled to the output terminal of the gain modulation circuit, and the multiplying circuit is configured to control a gain of the input voltage and provide a modulated input voltage signal at the output terminal of the multiplying circuit; a first latch circuit, having a set terminal, a reset terminal and an output terminal, wherein the set terminal is configured to receive a detecting signal, the reset terminal is coupled to the charge comparison circuit to receive the charge comparison signal; and an AND gate, having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is coupled to the output terminal of the switching control circuit, the second input terminal is coupled to the output terminal of the first latch circuit, and the output terminal is coupled to the switching circuit; wherein when the charge signal is larger than the charge reference signal, the first latch circuit is reset to turn OFF the switching circuit; and wherein when the detecting signal indicates that a new input cycle of the input voltage begins, the first latch circuit is set, and the switching circuit is turned ON and turned OFF by the switching control circuit.

5 . The control circuit of claim 4 , wherein the switching control circuit further comprises:
a current comparison circuit, having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is configured to receive the modulated input voltage signal, the second input terminal is configured to receive an input current feedback signal, and the output terminal is configured to provide a current comparison signal via comparing the input current feedback signal with the modulated input voltage signal; and a second latch circuit, having a set terminal, a reset terminal and an output terminal, wherein the set terminal is configured to receive a set signal, the reset terminal is coupled to the output terminal of the current comparison circuit, and the output terminal is coupled to the first input terminal of the AND gate, and wherein the switching circuit is turned ON based on the set signal, and the switching circuit is turned OFF based on the current comparison signal.

6 . The control circuit of claim 4 , wherein the gain modulation circuit is configured to provide a gain increasing signal and a gain decreasing signal to the multiplying circuit, and wherein
when the charge signal is larger than the charge reference signal, or when the input voltage decreases to zero, the gain decreasing signal transits to a first state from a second state, and when a TRIAC dimmer is turned ON, the gain decreasing signal transits to the second state from the first state; when the input voltage decreases to a predetermined voltage threshold, the gain increasing signal transits to the first state from the second state, and when the TRIAC dimmer is turned ON, the gain increasing signal transits to the second state from the first state; when the gain increasing signal is the first state and the gain decreasing signal is the second state, the gain of the input voltage increases; when the gain increasing signal is the second state and the gain decreasing signal is the first state, the gain of the input voltage decreases; and when both of the gain increasing signal and the gain decreasing signal are the first state or when both of the gain increasing signal and the gain decreasing signal are the second state, the gain of the input voltage maintains.

7 . The control circuit of claim 4 , wherein the charge reference signal generator further comprises:
a low pass filter, having an input terminal and an output terminal, wherein the input terminal is configured to receive the input voltage, and the output terminal is configured to provide an average of the input voltage via implementing a low pass filtering operation on the input voltage during a time period; and a clamp circuit, having an input terminal and an output terminal, wherein the input terminal is coupled to the output terminal of the low pass filter, and the output terminal is configured to provide the charge reference signal, the charge reference signal is updated to equal the average of the input voltage at an end of the time period.

8 . The control circuit of claim 1 , further comprises a signal converting circuit, having an input terminal and an output terminal, wherein the input terminal is configured to receive an input current feedback signal representative of

Assignees

• Chengdu Monolithic Power Sys

Inventors

• Kuang Naixing

Classifications

• H02M7/217

  using semiconductor devices only · CPC title

• H02M3/33507 Primary

  with automatic control of the output voltage or current, e.g. flyback converters (H02M3/33561, H02M3/33569 take precedence) · CPC title

• H02M3/33523 Primary

  with galvanic isolation between input and output of both the power stage and the feedback loop · CPC title

• H02M3/33561

  having more than one ouput with independent control · CPC title

• H05B45/59

  for reducing or suppressing flicker or glow effects · CPC title