Power converter, LED driver and control method

Patent metadata

Field	Value
Publication number	US-10638562-B2
Application number	US-201816210102-A
Country	US
Kind code	B2
Filing date	Dec 5, 2018
Priority date	Dec 15, 2017
Publication date	Apr 28, 2020
Grant date	Apr 28, 2020

Abstract

A power converter for an LED driver, can include: an input capacitor circuit coupled between input terminals of the power converter and being configured to receive an output signal of a rectifier circuit; a transistor coupled in series with an LED load; and a control circuit configured to regulate a capacitance value of the input capacitor circuit to regulate an input current, and to control the transistor to regulate a current flowing through the LED load.

First claim

What is claimed is:

1. A power converter configured for a light-emitting diode (LED) driver, the power converter comprising:
a) an input capacitor circuit comprising a first capacitor and a switch coupled in series between input terminals of said power converter, and being configured to receive an output signal of a rectifier circuit;
b) a transistor coupled in series with an LED load; and
c) a control circuit configured to control said switch to regulate a capacitance value of said input capacitor circuit to regulate an input current of said power converter, and to control said transistor to regulate a current flowing through said LED load.

2. The power converter of claim 1 , wherein said control circuit is configured to control said switch to turn on and off alternately in each power frequency half-wave period.

3. The power converter of claim 2 , wherein:
a) said control circuit is configured to control said switch to be turned off for a time length in each power frequency half-wave period to reduce a charging time of said first capacitor; and
b) said time length is a predetermined time duration.

4. The power converter of claim 2 , wherein said control circuit is configured to control said switch to be turned off for a predetermined time such that an input current of said power converter is substantially concentrated during a time period during which a voltage difference at two power terminal of said transistor is less than a predetermined value.

5. The power converter of claim 2 , further comprising a unidirectional conduction circuit coupled in parallel with said switch, wherein said unidirectional conduction circuit, said first capacitor, said transistor, and said LED load form a current loop circuit when an absolute value of an alternating current input voltage of said rectifier circuit is less than an input voltage of said power converter.

6. The power converter of claim 2 , wherein:
a) said control circuit is configured to control said switch to be turned on when a voltage difference between the two power terminals of said transistor is less than a predetermined value;
b) an absolute value of an alternating current input voltage of said rectifier circuit is not less than an input voltage of said power converter for at least part of a time when said switch is turned on; and
c) said switch is controlled to be turned off when said voltage difference is greater than said predetermined value.

7. The power converter of claim 6 , wherein said transistor is a field-effect transistor.

8. The power converter of claim 7 , wherein:
a) said transistor operates at a constant current region when said voltage difference is greater than said predetermined value; and
b) said transistor operates at a variable resistance region when said voltage difference is less than said predetermined value.

9. The power converter of claim 4 , wherein:
a) said control circuit is configured to control said switch to be turned off for said time length when an input sampling voltage is increased to be greater than a compensation signal;
b) said input sampling voltage characterizes an input voltage of said power converter; and
c) said compensation signal characterizes error information between said output current and a desired current value.

10. The power converter of claim 9 , wherein said time length is set such that an absolute value of an alternating current input voltage of said rectifier circuit is less than said input voltage of said power converter.

11. The power converter of claim 9 , wherein said control circuit comprises:
a) a compensation signal generating circuit configured to generate said compensation signal in accordance with said input sampling voltage and a reference voltage, wherein said compensation signal is used to control said transistor, and said input sampling voltage is used to characterize one of said output current and said input current;
b) a comparator configured to receive said input sampling voltage at a first input terminal, and said compensation signal at a second input terminal; and
c) a single triggered circuit configured to generate a control signal in response to a transition of an output signal of said comparator.

12. The power converter of claim 2 , wherein said power converter further comprises a second capacitor coupled between said input terminals.

13. The power converter of claim 2 , wherein said switch comprises a transistor having a body diode.

14. The power converter of claim 1 , wherein said LED load is coupled between output terminals of said power converter without an output capacitor connected thereto.

15. The power converter of claim 1 , wherein said capacitance value of said input capacitor circuit is regulated in accordance with a compensation signal representing error information between said output current and a desired current value and an input voltage of said power converter.

16. A method of controlling a light-emitting diode (LED) driver, the method comprising:
a) obtaining a sampling voltage representing an input voltage of a power converter of said LED driver, wherein said power converter comprises a switch and a first capacitor coupled in series between output terminals of a rectifier circuit;
b) controlling, by a control circuit, said switch to be turned off for a time length in each power frequency half-wave period to reduce a charging time of said first capacitor; and
c) controlling, by said control circuit, a transistor to regulate a current flowing through an LED load, wherein said transistor is coupled in series with said LED load.

17. The method of claim 16 , wherein said switch is controlled to be turned off for said time length, such that an input current of said LED driver is substantially concentrated during a time period in which a voltage difference at two power terminals of a transistor is less than a predetermined value.

18. The method of claim 17 , wherein:
a) said switch is turned on when a voltage difference between said two power terminals of said transistor is less than said predetermined value;
b) an absolute value of an alternating current input voltage of said rectifier circuit is not less than an input voltage of said power converter for at least part of a time duration when said switch is turned on; and
c) said switch is controlled to be turned off when said voltage difference is greater than said predetermined value.

19. The method of claim 17 , wherein:
a) said switch is turned off for said time length when an input sampling voltage is increased to be greater than a compensation signal;
b) said input sampling voltage characterizes an input voltage of said power converter; and
c) said compensation signal characterizes an error information between said output current and a desired current value.

20. The method of claim 17 , wherein said time length is set such that an absolute value of the alternating current input voltage of said rectifier circuit is less than an input voltage of said power converter.

Assignees

• Silergy Semiconductor Technology Hangzhou Ltd

Inventors

• Huang Qiukai
• Wang Jianxin
• Zheng Qingliang

Classifications

• H05B45/37 Primary

  Converter circuits · CPC title

• H05B45/36

  Circuits for reducing or suppressing harmonics, ripples or electromagnetic interferences [EMI] · CPC title

• H05B45/14

  using electrical feedback from LEDs or from LED modules · CPC title

• H05B33/0815 Primary

  Electricity · mapped topic

• H05B33/0812

  Electricity · mapped topic