LED driving circuit having SCR dimmer, circuit module and control method thereof

Patent metadata

Field	Value
Publication number	US-10285229-B2
Application number	US-201815935239-A
Country	US
Kind code	B2
Filing date	Mar 26, 2018
Priority date	Apr 6, 2017
Publication date	May 7, 2019
Grant date	May 7, 2019

Abstract

An apparatus can include: a bleeder circuit coupled to a DC bus of an LED driving circuit having an SCR dimmer; the bleeder circuit being configured to stabilize a voltage of the DC bus at a predetermined value by drawing a bleed current through a bleed path in a first mode, and to cut off the bleed path in a second mode; and a controller configured to control the bleeder circuit to be in the first mode before the SCR dimmer is turned on, and to switch to the second mode after the SCR dimmer is turned on, where the predetermined value is greater than zero.

First claim

What is claimed is:

1. An apparatus, comprising:
a) a bleeder circuit coupled to a DC bus of a light-emitting diode (LED) driving circuit having a silicon-controlled rectifier (SCR) dimmer;
b) a mode switch coupled to said bleeder circuit, and being configured to control said bleeder circuit to operate in a first mode or a second mode;
c) wherein said bleeder circuit is configured to stabilize a voltage of said DC bus at a predetermined value by drawing a bleed current through a bleed path in said first mode, and to cut off said bleed path in said second mode; and
d) a controller comprising said mode switch, and being configured to control said bleeder circuit to be in said first mode before said SCR dimmer is turned on, and to switch to said second mode after said SCR dimmer is turned on, wherein said predetermined value is greater than zero.

2. The apparatus of claim 1 , wherein said predetermined value is configured such that said DC bus voltage is greater than a predetermined load driving voltage when said SCR dimmer is turned on.

3. The apparatus of claim 1 , wherein said controller is configured to determine an on state of said SCR dimmer by detecting a rising speed of said DC bus voltage.

4. The apparatus of claim 1 , wherein said controller is configured to control said bleeder circuit to switch to said first mode when said DC bus voltage is below a predetermined threshold.

5. The apparatus of claim 1 , wherein said bleeder circuit comprises a transistor having two power terminals coupled to two terminals of said DC bus, said transistor being configured to regulate said DC bus voltage in accordance with a signal at a control terminal of said transistor.

6. The apparatus of claim 5 , wherein said bleeder circuit further comprises a maximum current clamp circuit coupled in series with said transistor, and being configured to limit a maximum value of said bleed current.

7. The apparatus of claim 1 , wherein said controller comprises a transconductance amplifier configured to receive a voltage reference signal at a first input terminal, and a bus voltage sampling signal at a second terminal, and to generate a control signal at an output terminal that is coupled to said mode switch.

8. The apparatus of claim 7 , wherein said mode switch is coupled between said output terminal of said transconductance amplifier and ground.

9. The apparatus of claim 7 , wherein said apparatus further comprises a voltage dividing circuit configured to divide said DC bus voltage, and to generate said bus voltage sampling signal, said DC bus voltage being greater than said predetermined load driving voltage by adjusting a voltage dividing ratio of said voltage dividing circuit when said SCR dimmer is turned on.

10. The apparatus of claim 9 , wherein said predetermined value is configured to be regulated by adjusting said voltage dividing ratio.

11. The apparatus of claim 7 , wherein said controller further comprises a mode switching circuit configured to turn on said mode switch when said bus voltage sampling signal is increased from a first threshold to a second threshold within a predetermined time, and to turn off said mode switch when said bus voltage sampling signal is decreased to be below a third threshold.

12. The apparatus of claim 11 , wherein said mode switching circuit comprises:
a) a first comparator configured to compare said bus voltage sampling signal against said first threshold;
b) a single pulse trigger circuit configured to generate a pulse signal for a predetermined time in response to an output signal of said first comparator;
c) a second comparator configured to compare said bus voltage sampling signal against said second threshold;
d) an AND-gate having two input terminals coupled to output terminals of said single pulse trigger circuit and said second comparator;
e) a third comparator configured to compare said bus voltage sampling signal against said third threshold; and
f) a RS flip-flop having a set terminal coupled to an output terminal of said AND-gate, a reset terminal coupled to an output terminal of said third comparator, and an output terminal coupled to a control terminal of said mode switch, wherein said first threshold is greater than said second threshold, and said second threshold is greater than said third threshold.

13. The apparatus of claim 1 , wherein said bleeder circuit comprises:
a) a Zener diode; and
b) a bleed switch, wherein said Zener diode, said bleed switch, and said maximum current clamp circuit are coupled in series to receive said DC bus voltage, and said bleed switch is configured to control said bleeder circuit to operate in said first mode or said second mode.

14. The apparatus of claim 13 , wherein said controller is configured to turn off said bleed switch when a bus voltage sampling signal is increased from a first threshold to a second threshold within a predetermined time, and to turn on said bleed switch when said bus voltage sampling signal is decreased to be below a third threshold.

15. The apparatus of claim 14 , wherein said controller comprises:
a) a first comparator configured to compare said bus voltage sampling signal against said first threshold;
b) a single pulse trigger circuit configured to generate a pulse signal for a predetermined time in response to an output signal of said first comparator;
c) a second comparator configured to compare said bus voltage sampling signal against said second threshold;
d) an AND-gate having input terminals coupled to output terminals of said single pulse trigger circuit and said second comparator;
e) a third comparator configured to compare said bus voltage sampling signal against said third threshold; and
f) a RS flip-flop having a set terminal coupled to an output terminal of said AND-gate, a reset terminal coupled to an output terminal of said third comparator, and an output terminal coupled to a control terminal of said bleed switch, wherein said first threshold is greater than said second threshold, and said second threshold is greater than said third threshold.

16. The apparatus of claim 13 , wherein said DC bus voltage is made greater than a predetermined load driving voltage by adjusting a breakdown voltage of said Zener diode when said SCR dimmer is turned on.

17. The apparatus of claim 16 , wherein said predetermined value is regulated by adjusting said breakdown voltage of said Zener diode.

18. A method of controlling a bleeder circuit coupled to a DC bus of a light-emitting diode (LED) driving circuit having a silicon-controlled rectifier (SCR) dimmer, the method comprising:
a) controlling, by a mode switch coupled to said bleeder circuit, said bleeder circuit to operate in a first mode or a second mode;
b) stabilizing, by said bleeder circuit, a voltage of said DC bus at a predetermined value by drawing a bleed current through a bleed path in said first mode;
c) cutting off, by said bleeder circuit, said bleed path in said second mode; and
d) controlling said bleeder circuit to be in said first mode before said SCR dimmer is turned on, and to switch to said second mode after said SCR dimmer is turned on, wherein said predetermined value is greater than zero.

19. The method of claim 18 , wherein said predetermined value is configured such that said DC bus voltage is greater than a predetermined load driving voltage.

20. The method of claim 19 , wherein said DC bus voltage is rapidly increased when said SCR dimmer is turned on by limiting the maximum value of said bleed current.

Assignees

• Silergy Semiconductor Technology Hangzhou Ltd

Inventors

• Wang Jianxin
• Chen Huiqiang

Classifications

• H05B33/0815 Primary

  Electricity · mapped topic

• H05B33/0845

  Electricity · mapped topic

• H05B33/0809

  Electricity · mapped topic

• H05B45/31

  Phase-control circuits · CPC title

• H05B45/3575

  by means of dummy loads or bleeder circuits, e.g. for dimmers · CPC title