LIGHT EMITTING DEVICE DRIVER CIRCUIT AND CONTROL CIRCUIT AND CONTROL METHOD THEREOF

• US 20140285109A1
• Filed: 03/15/2014
• Published: 09/25/2014
• Est. Priority Date: 03/21/2013
• Status: Abandoned Application

• Current Assignee: Richtek Technology Corporation (MediaTek, Inc.)
• Original Assignee: Richtek Technology Corporation (MediaTek, Inc.)
• Inventors: Liao, Chia-Wei, Hsiu, Leng-Nien
• Application Number:
  US14/214,747
• Publication Number:
  US 20140285109A1
• Time in Patent Office: Days
• US Class Current: 315/291
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/385 using flyback topology
• CPC Class Codes: H05B 45/39 Circuits containing inverter bridges

Abstract

The present invention discloses a light emitting device driver circuit and a control circuit and a control method thereof. The light emitting device driver circuit converts an input voltage to an output voltage, and provides an output current to a light emitting device circuit. The present invention detects whether the output voltage exceeds a predetermined level, and if no, the regulation target of the output current is set to a relatively higher current to fast charge an output capacitor; if yes, the output current is regulated to a desired target, wherein the relatively higher current is higher than the desired target.

Claims

1. A light emitting device driver circuit comprising:

a power stage circuit, for operating at least one power switch therein according to an operation signal to convert an input voltage to an output voltage, and to provide an output current to a light emitting device circuit;

an output capacitor, which is coupled to the output voltage; and

a control circuit, which is coupled to the power stage circuit, for generating the operation signal according to a feedback signal related to the output current and according to information related to the output voltage;

wherein when the output voltage does not exceed a predetermined level, the power stage circuit is controlled to fast charge the output capacitor, and when the output voltage exceeds the predetermined level, the power stage circuit is controlled to regulate the output current to a desired target, wherein before the power stage circuit starts a present operation or in a last turned OFF stage of the light emitting device circuit, there is a previous setting for the output current which corresponds to a preset charging current to the output capacitor in a condition that the output capacitor requires to be charged, and the power stage circuit fast charges the output capacitor with a relatively higher current which is higher than the preset charging current.

2. The light emitting device driver circuit of claim 1, wherein the predetermined level is equal to or lower than a threshold conduction forward bias of the light emitting device circuit.

3. The light emitting device driver circuit of claim 2, wherein the predetermined level is higher than or equal to 90% of the threshold conduction forward bias, and is lower than 100% of the threshold conduction forward bias.

4. The light emitting device driver circuit of claim 1, wherein the control circuit controls the power stage circuit to regulate the output current to the desired target, and the control circuit further adjusts the desired target according to a dimming control signal when the output voltage exceeds the predetermined level.

5. The light emitting device driver circuit of claim 1, wherein the output capacitor is fast charged by increasing a regulation target of the output current.

6. The light emitting device driver circuit of claim 5, wherein the control circuit adjusts the regulation target of the output current or the predetermined level according to temperature information.

7. A light emitting device control circuit, for generating an operation signal to control a power stage circuit such that an input voltage is converted to an output voltage across an output capacitor and an output current is provided to a light emitting device circuit, the light emitting device control circuit comprising:

a selection circuit, for selecting a first reference level or a fast charging reference;

a first comparison circuit, for comparing an output of the selection circuit with a feedback signal related to the output current, and generating a first comparison result;

an operation signal generation circuit, for generating the operation signal according to the first comparison result; and

a second comparison circuit, for comparing a voltage sensing signal related to the output voltage with a second reference level, and generating a second comparison result to determine whether the first reference level or the fast charging reference is selected by the selection circuit;

wherein the light emitting device control circuit sets a regulation target of the output current according to the fast charging reference to fast charge the output capacitor when the output voltage does not exceed a predetermined level corresponding to the second reference level, and sets a regulation target of the output current according to the first reference level when the output voltage exceeds the predetermined level.

8. The light emitting device control circuit of claim 7, wherein the predetermined level is equal to or lower than a threshold conduction forward bias of the light emitting device circuit.

9. The light emitting device control circuit of claim 7, wherein the predetermined level is higher than or equal to 90% of the threshold conduction forward bias, and is lower than 100% of the threshold conduction forward bias.

10. The light emitting device control circuit of claim 7, wherein the first reference level is adjustable.

11. The light emitting device control circuit of claim 7, wherein the fast charging reference or the second reference level is adjustable.

12. A light emitting device control method, for operating a power stage circuit to convert an input voltage to an output voltage across an output capacitor, and to provide an output current to a light emitting device circuit, the light emitting device control method comprising:

detecting whether the output voltage exceeds a predetermined level;

setting a regulation target of the output current to a relatively higher current for fast charging the output capacitor when the output voltage does not exceed the predetermined level; and

regulating the output current at a desired target when the output voltage exceeds the predetermined level, wherein the relatively higher current is higher than the desired target.

13. The control method of claim 12, wherein the desired target is a setting of the output current before the power stage circuit starts a present operation or in a last turned OFF stage of the light emitting device circuit, and the setting of the output current corresponds to a relatively lower brightness of the light emitting device circuit, and wherein the relatively higher current corresponds to a maximum brightness of the light emitting device circuit.

14. The control method of claim 12, wherein the relatively higher current is a maximum current allowed to be supplied by the power stage circuit.

15. The control method of claim 12, wherein the predetermined level is equal to or lower than a threshold conduction forward bias of the light emitting device circuit.

16. The control method of claim 15, wherein the predetermined level is higher than or equal to 90% of the threshold conduction forward bias, and is lower than 100% of the threshold conduction forward bias.

17. The control method of claim 12, further comprising:

adjusting the desired target according to a dimming control signal when the output voltage exceeds the predetermined level.

18. The control method of claim 12, further comprising:

adjusting the relatively higher current of the output current or the predetermined level according to temperature information.