LED driver using a depletion mode transistor to serve as a current source

• US 20050275711A1
• Filed: 06/10/2005
• Published: 12/15/2005
• Est. Priority Date: 06/14/2004
• Status: Active Grant

• Current Assignee: Richtek Technology Corporation (MediaTek, Inc.)
• Original Assignee: Richtek Technology Corporation (MediaTek, Inc.)
• Inventors: Liu, Jing-Meng, Pai, Chung-Lung, Su, Hung-Der
• Granted Patent: US 7,728,529 B2
• Time in Patent Office: Days
• US Class Current: 347/237
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

In a LED driver using a depletion mode transistor to serve as a current source, the depletion mode transistor is self-biased for providing a driving current to drive at least one LED, thereby requesting no additional control circuit to control the depletion mode transistor. The driving current is independent on the supply voltage coupled to the at least one LED, thereby requesting no additional voltage regulator, reducing the circuit size, and lowering the cost.

Claims

1. A LED driver comprising:

at least one LED coupled with a supply voltage; and

a current source including a depletion mode transistor self-biased for providing a driving current to drive the at least one LED.

2. The LED driver of claim 1, further comprising a switch for switching the driving current.

3. The LED driver of claim 1, wherein the depletion mode transistor is a MOSFET.

4. The LED driver of claim 3, wherein the MOSFET has a threshold voltage lower than −

0.5V.

5. The LED driver of claim 1, wherein the depletion mode transistor is a JFET.

6. The LED driver of claim 5, wherein the at least one LED and current source are integrated in a chip.

7. The LED driver of claim 5, further comprising a switch for switching the driving current.

8. The LED driver of claim 7, wherein the at least one LED, current source and switch are integrated in a chip.

9. The LED driver of claim 2, further comprising a controller for switching the switch.

10. The LED driver of claim 9, wherein the controller comprises a PWM or PFM controller.