LED array control circuit with voltage adjustment function and driver circuit and method for the same

• US 20110204797A1
• Filed: 05/24/2010
• Published: 08/25/2011
• Est. Priority Date: 02/25/2010
• Status: Active Grant

• Current Assignee: Richtek Technology Corporation (MediaTek, Inc.)
• Original Assignee: Richtek Technology Corporation (MediaTek, Inc.)
• Inventors: Liu, Ti-Ti, Lin, Shui-Mu
• Granted Patent: US 8,319,442 B2
• Time in Patent Office: Days
• US Class Current: 315/161
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines

Abstract

The present invention discloses an LED array control circuit with voltage adjustment function and a driver circuit and a method for the same. The LED array includes multiple LED strings each of which has multiple LED devices connected in series. The LED array control circuit includes: a power supply circuit for providing a supply voltage to the LED array; and an LED driver circuit for controlling current through each LED string, the LED driver circuit including: multiple current sources corresponding to the multiple LED strings respectively, each current source having a first end which is coupled to a corresponding LED string, and a second end; and a voltage adjustment circuit for adjusting a voltage of the second end of a corresponding current source according to a signal indicating a voltage drop across the corresponding LED string.

Claims

1. An LED array control circuit with voltage adjustment function, for controlling an LED array which includes multiple LED strings, each LED string having multiple LED devices connected in series;

each LED string having a first end and a second end, and all the first ends being coupled to a common node, the LED array control circuit comprising;

a first power supply circuit coupled to the common node for providing a supply voltage to the LED array; and

an LED driver circuit for controlling current through each LED string, the LED driver circuit including;

multiple current sources corresponding to the multiple LED strings respectively, each current source having a first end and a second end, wherein the first end of each current source is coupled to the second end of a corresponding LED string; and

a voltage adjustment circuit for adjusting a voltage of the second end of a corresponding current source according to a signal indicating a voltage drop across the corresponding LED string.

2. The LED array control circuit of claim 1, further comprising:

a second power supply circuit coupled to the LED driver circuit, which provides at least one voltage as an option for the second end of the corresponding current source to be coupled to.

3. The LED array control circuit of claim 2, wherein the second power supply circuit includes one or a combination of more than one of:

a buck switching regulator, a boost switching regulator, an inverter switching regulator, a buck-boost switching regulator, an inverter-boost switching regulator, a linear regulator, and a charge pump.

4. The LED array control circuit of claim 2, wherein the LED driver circuit further includes a charge pump which receives the voltage provided from the second power supply circuit and generates a different voltage as another option for the second end of the corresponding current source to be coupled to.

5. The LED array control circuit of claim 1, wherein the signal indicating the voltage drop across the corresponding LED string is obtained from the second end of the corresponding LED string.

6. The LED array control circuit of claim 1, wherein the voltage adjustment circuit includes:

a comparator for comparing the signal indicating the voltage drop across the corresponding LED string with a reference voltage and determining how to adjust the voltage of the second end of the corresponding current source thereby.

7. The LED array control circuit of claim 1, wherein:

the LED driver circuit further includes multiple switches for selectively connecting the second end of the corresponding current source to a chosen voltage level; and

the voltage adjustment circuit includes;

multiple comparators for comparing the signal indicating the voltage drop across the corresponding LED string with multiple reference voltages; and

a switch operation circuit for controlling the multiple switches according to the comparison results of the multiple comparators.

8. The LED array control circuit of claim 1, wherein the first power supply circuit provides a negative voltage, and the second end of each current source is coupled to ground or a positive voltage.

9. An LED driver circuit with voltage adjustment function, for controlling current through LEDs of an LED array, the LED array including multiple LED strings, each LED string having multiple LED devices connected in series;

each LED string having a first end and a second end, and all the first ends being coupled to a power supply circuit, the LED driver circuit comprising;

multiple current sources corresponding to the multiple LED strings respectively, each current source having a first end and a second end, wherein the first end of each current source is coupled to the second end of a corresponding LED string; and

a voltage adjustment circuit for adjusting a voltage of the second end of a corresponding current source according to a signal indicating a voltage drop across the corresponding LED string.

10. The LED driver circuit of claim 9, further comprising a charge pump which receives a voltage provided from external of the LED driver circuit and generates a different voltage as an option for the second end of the corresponding current source to be coupled to.

11. The LED driver circuit of claim 9, wherein the signal indicating the voltage drop across the corresponding LED string is obtained from the second end of the corresponding LED string.

12. The LED driver circuit of claim 9, wherein the power supply circuit provides a negative voltage, and the second end of each current source is coupled to ground or a positive voltage.

13. The LED driver circuit of claim 9, wherein the voltage adjustment circuit includes:

a comparator for comparing the signal indicating the voltage drop across the corresponding LED string with a reference voltage and determining how to adjust the voltage of the second end of the corresponding current source thereby.

14. The LED driver circuit of claim 9, further comprising:

multiple switches for selectively connecting the second end of the corresponding current source to a chosen voltage level; and

wherein the voltage adjustment circuit includes;

multiple comparators for comparing the signal indicating the voltage drop across the corresponding LED string with multiple reference voltages; and

a switch operation circuit for controlling the multiple switches according to comparison results of the multiple comparators.

15. The LED driver circuit of claim 9, wherein each current source includes:

a transistor;

a resistor having a first end coupled to one end of the transistor, and a second end coupled to a node; and

an operational amplifier having an input terminal coupled to the first end of the resistor, another input terminal receiving a voltage which is equal to a voltage at the node plus a bias voltage, and an output controlling the transistor.

16. A method for controlling an LED array with voltage adjustment, comprising:

providing an LED array which includes multiple LED strings;

coupling each LED string with one end of a corresponding current source which controls current through the corresponding LED string; and

adjusting a voltage of the other end of the corresponding current source according to a voltage drop across the corresponding LED string.

17. The method of claim 16, further comprising:

providing at least one voltage other than ground, as an option for adjusting the voltage of the other end of the current source to.

18. The method of claim 16, further comprising:

providing at least one positive voltage and one negative voltage level as options for adjusting the voltage of the other end of the current source to.