LIGHT EMITTING DEVICE CONTROL CIRCUIT WITH DIMMING FUNCTION AND CONTROL METHOD THEREOF

• US 20150173153A1
• Filed: 12/04/2014
• Published: 06/18/2015
• Est. Priority Date: 12/16/2013
• Status: Active Grant

• Current Assignee: Richtek Technology Corporation (MediaTek, Inc.)
• Original Assignee: Richtek Technology Corporation (MediaTek, Inc.)
• Inventors: Hsiu, Leng-Nien, Chen, Pei-Yuan, Chen, Chien-Yang
• Granted Patent: US 9,247,601 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]

Abstract

The present invention discloses a light emitting device control circuit with dimming function and a control method thereof. The light emitting device control circuit includes: a dimmer circuit, a rectifier and filter circuit, a power converter circuit, and a headroom voltage regulation circuit. The dimmer circuit generates an AC dimming voltage according to an AC voltage. The rectifier and filter circuit generates an input voltage according to the AC dimming voltage. The power converter circuit operates according to a control signal to convert the input voltage to an output voltage which is supplied to a light emitting device circuit. The headroom voltage regulation circuit generates the control signal according to a reference value and a difference between the input voltage and the output voltage, and regulates the difference at a level corresponding to the reference value by a feedback control loop.

Claims

1. A light emitting device control circuit with dimming function, comprising:

a dimmer circuit for generating an AC dimming voltage according to an AC voltage;

a rectifier and filter circuit, which is coupled to the dimmer circuit, for generating an input voltage according to the AC dimming voltage;

a power converter circuit, which is coupled to the rectifier and filter circuit, for operating at least one power switch therein according to a control signal to convert the input voltage to an output voltage, wherein the output voltage is supplied to a light emitting device circuit; and

a headroom voltage regulation circuit, which is coupled to the power converter circuit, for generating the control signal according to a reference value and a difference between the input voltage and the output voltage, and regulating the difference at a level corresponding to the reference value by a feedback control loop.

2. The light emitting device control circuit with dimming function of claim 1, wherein the headroom voltage regulation circuit includes:

a difference sampling circuit, for generating a headroom voltage according to the difference; and

a comparison circuit, which is coupled to the difference sampling circuit, for generating the control signal according to the headroom voltage and a reference voltage, wherein the reference voltage corresponds to the reference value.

3. The light emitting device control circuit with dimming function of claim 2, wherein the difference sampling circuit includes a voltage divider circuit, which has a voltage divider node for generating the headroom voltage.

4. The light emitting device control circuit with dimming function of claim 3, wherein the difference sampling circuit further includes a capacitor, which is coupled to the voltage divider node of the divider circuit.

5. The light emitting device control circuit with dimming function of claim 1, wherein the headroom voltage regulation circuit includes:

an adder circuit or a subtractor circuit, for adding to or subtracting a reference voltage from a voltage corresponding and related to one of the input voltage and the output voltage, wherein the reference voltage corresponds to the reference value; and

a comparison circuit, which is coupled to the adder circuit or the subtractor circuit, for generating the control signal according to a voltage corresponding and related to the other one of the input voltage and the output voltage and an operation result of the adder or the subtractor circuit.

6. The light emitting device control circuit with dimming function of claim 2, wherein the reference voltage is adjustable.

7. The light emitting device control circuit with dimming function of claim 5, wherein the reference voltage is adjustable.

8. The light emitting device control circuit with dimming function of claim 1, further comprising an electronic transformer, which is coupled to the dimmer circuit, for receiving the AC dimming voltage to generate a high frequency AC dimming voltage for being inputted to the rectifier and filter circuit.

9. A control method of a light emitting device control circuit with dimming function, comprising:

receiving an input voltage, wherein the input voltage has an average value which is controllably changeable;

operating at least one power switch in a power converter circuit according to a control signal to convert the input voltage to an output voltage for being supplied to a light emitting device circuit; and

generating the control signal according to a reference value and a difference between the input voltage and the output voltage, and regulating the difference at a level corresponding to the reference value by a feedback control loop.

10. The control method of claim 9, wherein the step of regulating the difference at a level corresponding to the reference value includes:

generating a headroom voltage according to the difference; and

generating the control signal according to the headroom voltage and a reference voltage, wherein the reference voltage corresponds to the reference value.

11. The control method of claim 9, wherein the step of regulating the difference at a level corresponding to the reference value includes:

adding to or subtracting a reference voltage from a voltage corresponding and related to one of the input voltage and the output voltage, wherein the reference voltage corresponds to the reference value; and

generating the control signal according to a voltage corresponding and related to the other one of the input voltage and the output voltage and an operation result of the addition or the subtraction.

12. The control method of claim 10, wherein the reference voltage is adjustable.

13. The control method of claim 11, wherein the reference voltage is adjustable.