AUTOMOBILE LED DRIVING DEVICE

• US 20120074845A1
• Filed: 09/23/2011
• Published: 03/29/2012
• Est. Priority Date: 09/29/2010
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: AOKI, Akira, MIYAMOTO, Koji
• Granted Patent: US 8,754,592 B2
• Time in Patent Office: Days
• US Class Current: 315/119
• CPC Class Codes: B60Q 11/005 for lighting devices, e.g. indicating if lamps are burning or not
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/397 Current mirror circuits
• CPC Class Codes: H05B 45/50 responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
• CPC Class Codes: H05B 47/24 Circuit arrangements for protecting against overvoltage

Abstract

An automobile LED driving device includes a current setting portion to set multiple reference currents independently from one another for multiple respective current setting resistors connected externally, a current controller to select one of the multiple reference currents based on a control signal provided from outside, and an output transistor to control an output current to an automobile LED connected externally based on the reference current selected by the current controller.

Claims

1. An automobile LED driving device comprising:

a current setting portion to set multiple reference currents independently from one another for multiple respective current setting resistors connected externally,

a current controller to select one of the multiple reference currents based on a control signal provided from outside, and

an output transistor to control an output current to an automobile LED connected externally based on the reference current selected by the current controller.

2. The automobile LED driving device according to claim 1 further comprising:

a protect bus controller to generate a protect bus signal according to a detection of an abnormality and to perform an external input/output process for the protect bus signal,

wherein the current controller controls a current supply to the automobile LED based on the protect bus signal.

3. The automobile LED driving device according to claim 1 further comprising:

a LED ground short detector to detect the ground short of the automobile LED,

wherein the current controller turns OFF a supply of the output current forcibly when the ground short of the automobile LED occurs.

4. The automobile LED driving device according to claim 3, wherein the LED ground short detector comprises:

a first comparator to generate a LED ground short detection signal based on a comparison between a forward drop voltage of the automobile LED or a monitor voltage based on the forward drop voltage and a first threshold voltage, and

a ground short recovery circuit to generate the forward drop voltage by flowing current to the automobile LED when recovering the ground short of the automobile LED.

5. The automobile LED driving device according to claim 1 further comprising:

a LED open circuit detector to detect the open circuit of the automobile LED.

6. The automobile LED driving device according to claim 5, wherein the LED open circuit detector comprises:

a second comparator to generate a LED open circuit detection signal based on a comparison between a terminal voltage of an external terminal to which the automobile LED is connected externally and a second threshold voltage, and

an amplifier to generate a current restriction signal by amplifying a difference between the terminal voltage and a clamp voltage lower than the second threshold voltage,

wherein the current controller controls the output current to the automobile LED based on the current restriction signal so as the terminal voltage not to exceed the clamp voltage.

7. The automobile LED driving device according to claim 1, wherein the current setting portion generates the multiple reference currents by applying constant voltages to multiple respective current setting resistors.

8. The automobile LED driving device according to claim 1, wherein the current setting portion generates multiple current setting voltages by flowing constant currents to the multiple respective current setting resistors, and generates multiple reference currents by applying the multiple current setting voltages to respective internal resistors.

9. The automobile LED driving device according to claim 8, wherein negative characteristic thermistors are connected in parallel to the respective current setting resistors.

10. The automobile LED driving device according to claim 1, wherein the current controller comprises:

an input transistor forming a current mirror circuit with the output transistor and generating a mirror current to the output transistor according to the reference current provided to the input transistor.

11. The automobile LED driving device according to claim 10 further comprising:

a bias portion to equalize a voltage between the source-drain voltages of the input transistor and the output transistor.

12. The automobile LED driving device according to claim 2 further comprising:

a LED ground short detector to detect the ground short of the automobile LED,

wherein the current controller turns OFF a supply of the output current forcibly when the ground short of the automobile LED occurs.

13. The automobile LED driving device according to claim 12, wherein the LED ground short detector comprises:

a first comparator to generate a LED ground short detection signal based on a comparison between a forward drop voltage of the automobile LED or a monitor voltage according to the forward drop voltage and a first threshold voltage, and

a ground short recovery circuit to generate the forward drop voltage by flowing current to the automobile LED when recovering the ground short of the automobile LED.

14. The automobile LED driving device according to claim 2 further comprising:

a LED open circuit detector to detect the open circuit of the automobile LED.

15. The automobile LED driving device according to claim 14, wherein the LED open circuit detector comprises:

a second comparator to generate the LED open circuit detection signal based on a comparison between a terminal voltage of an external terminal to which the car LED is connected externally and a second threshold voltage, and

an amplifier to generate a current restriction signal by amplifying a difference between the terminal voltage and a clamp voltage lower than the second threshold voltage,

wherein the current controller controls the output current to the automobile LED based on the current restriction signal so as the terminal voltage not to exceed the clamp voltage.

16. The automobile LED driving device according to claim 3 further comprising:

a LED open circuit detector to detect the open circuit of the automobile LED.

17. The automobile LED driving device according to claim 16, wherein the LED open circuit detector comprises:

a second comparator to generate the LED open circuit detection signal based on a comparison between a terminal voltage of an external terminal to which the car LED is connected externally and a second threshold voltage, and

an amplifier to generate a current restriction signal by amplifying a difference between the terminal voltage and a clamp voltage lower than the second threshold voltage,

wherein the current controller controls the output current to the automobile LED based on the current restriction signal so as the terminal voltage not to exceed the clamp voltage.

18. The automobile LED driving device according to claim 4 further comprising:

a LED open circuit detector to detect the open circuit of the automobile LED.

19. The automobile LED driving device according to claim 18, wherein the LED open circuit detector comprises:

a second comparator to generate the LED open circuit detection signal based on a comparison between a terminal voltage of an external terminal to which the car LED is connected externally and a second threshold voltage, and

an amplifier to generate a current restriction signal by amplifying a difference between the terminal voltage and a clamp voltage lower than the second threshold voltage,

wherein the current controller controls the output current to the automobile LED based on the current restriction signal so as the terminal voltage not to exceed the clamp voltage.