# US 2011/0254469 A1 · Dimming circuit and method for leds

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- Number: US 2011/0254469 A1
- Document ID: US20110254469A1
- Status: Published application
- Kind: A1
- Application number: 13/081,131
- Filed: 2011-04-06
- Published: 2011-10-20
- Earliest claimed: 2010-04-14
- Assignees: Richpower Microelectronics Corporation
- Inventors: Chen-Jie RUAN; Chin-Hui Wang; Peng-Ju Lan
- Web page: https://patentgrep.com/patent/US20110254469A1

## CPC

- H05B 45/38: using boost topology
- H05B 45/14: using electrical feedback from LEDs or from LED modules
- H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL

## Abstract

A dimming circuit and method for a LED provide a first driving voltage or a second driving voltage according to a dimming signal provided by a functional IC to enable or disable the LED. The values of the first and second driving voltages are controlled so that overstressing of the LED is avoided while the functional IC is capable of working even when the LED is off. The LED's life time is thus prolonged.

## Claims

### Claim 1

A dimming circuit for supplying an output voltage to a LED according to a dimming signal provided by a functional IC, the dimming circuit comprising:
a selector connected to the functional IC, being controlled by the dimming signal to select one of a first driving voltage setting signal and a second driving voltage setting signal as an output of the selector; and
a power source connected to the functional IC and the selector, providing a first driving voltage or a second driving voltage as the output voltage according to the output of the selector, and supplying the output voltage to the functional IC.

### Claim 2 (depends on 1)

The dimming circuit of claim 1, further comprising a voltage setting circuit connected to the selector, providing the first driving voltage setting signal and the second driving voltage setting signal.

### Claim 3 (depends on 2)

The dimming circuit of claim 2, wherein the voltage setting circuit comprises:
a current sense resistor connected to the LED, detecting a current of the LED to generate a feedback signal;
a first error amplifier connected to the selector and the current sense resistor, amplifying a difference between the feedback signal and a first reference voltage to generate the first driving voltage setting signal; and
a second error amplifier connected to the selector and the power source, amplifying a difference between the output voltage and a second reference voltage to generate the second driving voltage setting signal.

### Claim 4 (depends on 3)

The dimming circuit of claim 3, wherein the second reference voltage is controlled by an off voltage setting signal.

### Claim 5 (depends on 1)

The dimming circuit of claim 1, wherein the power source provides a predefined current to the LED in a first one of two phases.

### Claim 6 (depends on 5)

The dimming circuit of claim 5, further comprising:
a voltage source connected to the selector, providing a reference voltage as the first driving voltage setting signal; and
an automatic voltage detector connected to the selector and the power source, detecting and recording a voltage of the LED in the first phase as the second driving voltage setting signal.

### Claim 7 (depends on 6)

The dimming circuit of claim 6, wherein the automatic voltage detector comprises:
a capacitor connected to the selector, recording and providing the second driving voltage setting signal; and
a switch connected between the LED and the capacitor, being controlled to connect the LED to the capacitor in the first phase.

### Claim 8

A dimming method for supplying an output voltage to a LED according to a dimming signal provided by a functional IC, the dimming method comprising the steps of:
(A) providing a first voltage setting signal and a second voltage setting signal;
(B) selecting one of the first voltage setting signal and the second voltage setting signal according to the dimming signal; and
(C) providing a first driving voltage or a second driving voltage as the output voltage according to the selected driving voltage setting signal, and supplying the output voltage to the functional IC.

### Claim 9 (depends on 8)

The dimming method of claim 8, wherein the step A comprises the steps of:
detecting a current of the LED to generate a feedback signal;
amplifying a difference between the feedback signal and a first reference voltage to generate the first voltage setting signal; and
amplifying a difference between the output voltage and a second reference voltage to generate the second voltage setting signal.

### Claim 10 (depends on 9)

The dimming method of claim 9, further comprising the step of adjusting the second reference voltage to change the second voltage setting signal.

### Claim 11 (depends on 7)

The dimming method of claim 7, wherein the step A comprises the steps of:
providing a reference voltage as the first voltage setting signal; and
in a first one of two phases, supplying a predefined current to the LED, and detecting and recording a voltage of the LED as the second voltage setting signal.