Multi-string LED driver with current balancing

Patent metadata

Field	Value
Publication number	US-9655174-B2
Application number	US-201514798596-A
Country	US
Kind code	B2
Filing date	Jul 14, 2015
Priority date	Jul 14, 2015
Publication date	May 16, 2017
Grant date	May 16, 2017

Abstract

The present invention discloses a current-source-output light-emitting-diode (LED) driver based on LCLC circuit to provide a constant output current regardless of variations in LED parameters. In the LCLC circuit, the number of additional capacitors is scalable with the number of LED strings for current balancing. Moreover, the input impedance of the improved LCLC circuit is designed to be resistive at the operating frequency to minimize reactive power. The conventional duty cycle control can easily incorporate zero-voltage-switching (ZVS).

First claim

What is claimed is:

1. A device for driving a plurality of LED strings with current balancing, comprising:
a T circuit comprising an input capacitor, a body inductor, and a plurality of output capacitors; and
at least one full-wave rectifier connecting one of the output capacitors of the T circuit to one of the LED strings, or at least one half-wave rectifier connecting one of the output capacitors of the T circuit to a pair of the LED strings;
wherein:
the input capacitor is selected to have a first capacitance value;
the output capacitors have a same value of capacitance; and
the same value of capacitance is given by the first capacitance value divided by the number of the output capacitors.

2. The device of claim 1 , wherein the T circuit further comprises an isolation transformer.

3. The device of claim 2 , wherein the T circuit further comprises a body inductor connected in parallel to the isolation transformer.

4. The device of claim 1 , further comprising a dimming switch connected in parallel to one of the LED strings.

5. The device of claim 4 , wherein the filter inductor and the input capacitor of the T circuit are configured such that one or more high order harmonics of an AC input to the T circuit are filtered out.

6. The device of claim 1 , further comprising a filter inductor connecting in series to the input capacitor of the T circuit.

7. The device of claim 1 , further comprising a full-bridge circuit connected to the input capacitor of the T circuit.

8. A device for driving a plurality of LED strings with current balancing, comprising:
a T circuit comprising an input capacitor, a body inductor, and a plurality of output capacitors, wherein the output capacitors have a same value of capacitance;
at least one full-wave rectifier connecting one of the output capacitors of the T circuit to one of the LED strings, or at least one half-wave rectifier connecting one of the output capacitors of the T circuit to a pair of the LED strings; and
a dimming switch connected in parallel to one of the LED strings.

Assignees

• Univ Hong Kong Polytechnic

Inventors

• Qu Xiaohui
• Wong Siu-Chung
• Tse Chi Kong

Classifications

• H05B45/35

  Balancing circuits · CPC title

• H05B45/46 Primary

  having LEDs disposed in parallel lines · CPC title

• H05B33/0827

  Electricity · mapped topic

• H05B33/0809 Primary

  Electricity · mapped topic

• H05B45/345

  Current stabilisation; Maintaining constant current · CPC title