DEVICE AND METHOD FOR DETECTING A SHORT-CIRCUITED LIGHT-EMITTING DIODE IN A LIGHT DEVICE OF A MOTOR VEHICLE

• US 20170006671A1
• Filed: 04/28/2016
• Published: 01/05/2017
• Est. Priority Date: 04/29/2015
• Status: Active Grant

• Current Assignee: Valeo Vision (Valeo SE)
• Original Assignee: Valeo Vision (Valeo SE)
• Inventors: LeSaffre, Olivier-Sebastien
• Granted Patent: US 9,668,317 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H05B 45/54 in a series array of LEDs
• CPC Class Codes: H05B 45/56 involving measures to prevent abnormal temperature of the LEDs
• CPC Class Codes: H05B 45/58 involving end of life detection of LEDs
• CPC Class Codes: H05B 47/23 of two or more light sources connected in series
• CPC Class Codes: H05B 47/235 with communication between the lamps and a central unit

Abstract

A light device that makes it possible to detect a short-circuited light-emitting diode in a series assembly of a plurality of such diodes. By taking into account the junction temperature of the diodes, the device and the method associated therewith make it possible to avoid false positive short-circuit detections. The device is also capable of learning the operating parameters necessary to the detection independently and dynamically, which makes it particularly adaptive.

Claims

1. A light device for a motor vehicle, said light device comprising:

driving means for powering a plurality of light-emitting diodes, LEDs, mounted in series, each of said LEDs being characterized by the same forward voltage V_f dependent on its junction temperature;

first means for measuring said junction temperature of said LEDs;

second means for measuring an electrical voltage at the terminals of an assembly; and

processing means for detecting a failure of at least one of said LEDs of said assembly;

wherein said processing means are configured to;

compare said electrical voltage at said terminals of said assembly measured at a first given instant to said electrical voltage at said terminals of said assembly measured at a second given instant, said comparison being conditional on the identity of said junction temperature of said LEDs measured at said first and second instants; and

detect a failure of at least one of said LEDs of said assembly as a function of said comparison.

2. The light device according to claim 1, wherein said light device comprises a memory element, said processing means being configured to read and write in said memory element and being configured to:

obtain, using said measurement means, a measurement T_mes indicative of said junction temperature of at least one of said LEDs and a measurement V_mes indicative of said electrical voltage at said terminals of said assembly at a given instant when said assembly is powered.

3. The light device according to claim 2, wherein said processing means are further configured to:

if said memory element contains a voltage value V_cal associated with said measurement T_mes, compare said measurement V_mes to said voltage value V_cal or to a comparison voltage directly dependent on said voltage value V_cal; and

conclude that one of said LEDs of said assembly is short-circuited as a function of said comparison.

4. The light device according to claim 3, wherein said processing means are configured to:

if said memory element contains said voltage value V_cal associated with said measurement T_mes, compare said measurement V_mes to (V_cal+/−

α

), 0<

α

≦

V_f

conclude that one of said LEDs of said assembly is short-circuited if V_mes<

(V_cal+/−

α

).

5. The light device according to claim 2, wherein said processing means are further configured to:

if said memory element does not contain any said voltage value associated with said measurement T_mes, store said measurement V_mes and associate said measurement V_mes with said measurement T_mes in said memory element.

6. The light device according to claim 2, wherein said processing means are further configured to update said voltage value V_cal stored by using said measurement V_mes, if V_mes≧

(V_cal+/−

α

).

17. The light device according to claim 3, wherein said processing means are further configured to:

if said memory element does not contain any said voltage value associated with said measurement T_mes, store said measurement V_mes and associate said measurement V_mes with said measurement T_mes in said memory element.

18. The light device according to claim 4, wherein said processing means are further configured to:

if said memory element does not contain any said voltage value associated with said measurement T_mes, store said measurement V_mes and associate said measurement V_mes with said measurement T_mes in said memory element.

19. The light device according to claim 3, wherein said processing means are further configured to update said voltage value V_cal stored by using said measurement V_mes, if V_mes≧

(V_cal+/−

α

).

20. The light device according to claim 4, wherein said processing means are further configured to update said voltage value V_cal stored by using said measurement V_mes, if V_mes≧

(V_cal+/−

α

).

7. A method for detecting a short-circuited light-emitting diode, LED, in a light device for a motor vehicle, said light device comprising:

driving means for powering a plurality of light-emitting diodes, LED, mounted in series, each of said LEDs being characterized by the same forward voltage V_f dependent on its junction temperature;

first means for measuring said junction temperature of said LEDs;

second means for measuring an electrical voltage at the terminals of an assembly;

processing means for detecting a failure of at least one of said LEDs of said assembly,

wherein said method comprises the following steps;

comparing said electrical voltage at said terminals of said assembly measured at a first given instant to said electrical voltage at said terminals of said assembly measured at a second given instant, said comparison being conditional on the identity of said junction temperature of said LEDs measured at said first and second instants; and

detecting a failure of at least one of said LEDs of said assembly as a function of said comparison.

8. The method according to claim 7, wherien said method comprises the following steps:

obtaining, using said measurement means, a measurement T_mes indicative of said junction temperature of at least one of said LEDs and a measurement V_mes indicative of said electrical voltage at said terminals of said assembly at a given instant when said assembly is powered.

9. The method according to claim 8, wherein said method comprises the following steps:

if a memory element of said light device contains a voltage value V_cal associated with said measurement T_mes, comparing said measurement V_mes to said voltage value V_cal or to a comparison voltage directly dependent on said voltage value V_cal;

concluding that one of said LEDs of said assembly is short-circuited as a function of said comparison.

10. The method according to claim 9, wherein said method comprises the following steps:

if said memory element contains a said voltage value V_cal associated with said measurement T_mes, comparing said measurement V_mes to (V_cal+/−

α

), 0<

α

≦

V_f;

concluding that one of said LEDs of said assembly is short-circuited if V_mes<

(V_cal+/−

α

).

11. The method according to claim 8, wherein said method comprises the following steps:

if said memory element does not contain any said voltage value associated with said measurement T_mes, storing said measurement V_mes and associating said measurement V_mes with said measurement T_mes in said memory element.

12. The method according to claim 8, wherein said method further comprises the step of updating said voltage value V_cal stored and associated with said measurement T_mes by using said measurement V_mes, if V_mes≧

(V_cal+/−

α

).

13. The method according to claim 8, wherein said method comprises an intermediate step of filtering of said measurements following said obtaining step, during which measurements not belonging to a predetermined range are discarded.

14. The method according to claim 8, wherein said steps are repeated periodically.

15. The method according to claim 8, wherein said steps are implemented if said junction temperature of said LEDs and said electrical voltage at said terminals of said assembly have generally constant values.

16. The method according to claim 7, wherein said method comprises a preliminary step of the provision of initial voltage values associated with a plurality of temperature values in said memory element.