Ground fault detection circuit, abnormality detection circuit, light emitting device, vehicle

Patent metadata

Field	Value
Publication number	US-9853439-B2
Application number	US-201715581260-A
Country	US
Kind code	B2
Filing date	Apr 28, 2017
Priority date	May 10, 2016
Publication date	Dec 26, 2017
Grant date	Dec 26, 2017

Abstract

A light emitting device includes a series connection unit constituted of N light emitting elements, a light emitting element driving circuit having an output terminal connected to an anode of the series connection unit, N short-circuit switches respectively connected in parallel to the light emitting elements, and a switch control unit arranged to control on and off of the short-circuit switches. A ground fault detection circuit, which detects a ground fault of the light emitting device, includes a reference voltage source arranged to generate a reference voltage, and a comparator arranged to compare the anode voltage of the series connection unit with the reference voltage. The reference voltage has a value smaller than the product of an on-resistance of one of the short-circuit switches and output current of the light emitting element driving circuit.

First claim

What is claimed is:

1. A ground fault detection circuit arranged to detect a ground fault of a light emitting device including a series connection unit constituted of N light emitting elements (N is a natural number equal to or larger than two), a light emitting element driving circuit having an output terminal connected to an anode of the series connection unit, N short-circuit switches respectively connected in parallel to the light emitting elements, and a switch control unit arranged to control on and off of the short-circuit switches, the ground fault detection circuit comprising:
an input portion to which an anode voltage of the series connection unit is input; and
a ground fault determination unit arranged to determine that a ground fault has occurred without a short-circuit switch in the ground fault path, when the anode voltage of the series connection unit input through the input portion is equal to or smaller than a predetermined value that is smaller than the product of an on-resistance of one of the short-circuit switches and output current of the light emitting element driving circuit.

2. The ground fault detection circuit according to claim 1 , wherein the ground fault determination unit includes
a reference voltage source arranged to generate a reference voltage having the predetermined value, and
a comparator arranged to compare the anode voltage of the series connection unit with the reference voltage.

3. A ground fault detection circuit arranged to detect a ground fault of a light emitting device including a series connection unit constituted of N light emitting elements (N is a natural number equal to or larger than two), a light emitting element driving circuit having an output terminal connected to an anode of the series connection unit, N short-circuit switches respectively connected in parallel to the light emitting elements, and a switch control unit arranged to control on and off of the short-circuit switches, the ground fault detection circuit comprising:
N short-circuit detection circuits arranged respectively to detect short-circuits in the light emitting elements; and
a ground fault determination unit arranged to determine that a ground fault has occurred without a short-circuit switch in the ground fault path, if all the N short-circuit detection circuits detect that short-circuits have occurred in all the N light emitting elements when the switch control unit makes all the N short-circuit switches be in off state.

4. An abnormality detection circuit comprising:
the ground fault detection circuit according to claim 1 ;
N short-circuit detection circuits arranged respectively to detect short-circuits in the light emitting elements; and
a short-circuit determination unit arranged to determine that a short circuit has occurred, if at least one of the short-circuit detection circuits detects that a short circuit has occurred in the light emitting element when the switch control unit makes all the N short-circuit switches be in off state.

5. An abnormality detection circuit comprising:
the ground fault detection circuit according to claim 3 ; and
a short-circuit determination unit arranged to determine that a short circuit has occurred, if at least one of the short-circuit detection circuits detects that a short circuit has occurred in the light emitting element when the switch control unit makes all the N short-circuit switches be in off state.

6. The abnormality detection circuit according to claim 4 , further comprising a signal generation unit arranged to generate an abnormality detection signal based on an output signal of the ground fault determination unit and an output signal of the short-circuit determination unit, wherein
the signal generation unit generates the abnormality detection signals having different waveforms between a case where the output signal of the ground fault determination unit is a signal indicating a ground fault without a short-circuit switch in the ground fault path, and a case where the output signal of the ground fault determination unit is not the signal indicating a ground fault without a short-circuit switch in the ground fault path while the output signal of the short-circuit determination unit is a signal indicating a short-circuit.

7. The abnormality detection circuit according to claim 5 , further comprising a signal generation unit arranged to generate an abnormality detection signal based on an output signal of the ground fault determination unit and an output signal of the short-circuit determination unit, wherein
the signal generation unit generates the abnormality detection signals having different waveforms between a case where the output signal of the ground fault determination unit is a signal indicating a ground fault without a short-circuit switch in the ground fault path, and a case where the output signal of the ground fault determination unit is not the signal indicating a ground fault without a short-circuit switch in the ground fault path while the output signal of the short-circuit determination unit is a signal indicating a short-circuit.

8. A light emitting device comprising:
the ground fault detection circuit according to claim 1 ;
a series connection unit constituted of N light emitting elements (N is a natural number equal to or larger than two);
a light emitting element driving circuit having an output terminal connected to an anode of the series connection unit;
N short-circuit switches respectively connected in parallel to the light emitting elements; and
a switch control unit arranged to control on and off of the short-circuit switches.

9. A light emitting device comprising:
the ground fault detection circuit according to claim 3 ;
a series connection unit constituted of N light emitting elements (N is a natural number equal to or larger than two);
a light emitting element driving circuit having an output terminal connected to an anode of the series connection unit;
N short-circuit switches respectively connected in parallel to the light emitting elements; and
a switch control unit arranged to control on and off of the short-circuit switches.

10. The light emitting device according to claim 8 , wherein the light emitting element is a light emitting diode or an organic EL element.

11. The light emitting device according to claim 9 , wherein the light emitting element is a light emitting diode or an organic EL element.

12. The light emitting device according to claim 8 , wherein the light emitting device is used as an in-vehicle lamp.

13. The light emitting device according to claim 9 , wherein the light emitting device is used as an in-vehicle lamp.

14. The light emitting device according to claim 12 , wherein the light emitting device is mounted in a vehicle as a headlight module, a turn lamp module, or a rear lamp module.

15. The light emitting device according to claim 13 , wherein the light emitting device is mounted in a vehicle as a headlight module, a turn lamp module, or a rear lamp module.

16. A vehicle comprising the light emitting device according to claim 12 .

17. A vehicle comprising the light emitting device according to claim 13 .

18. The vehicle arranged to claim 16 , wherein the light emitting device is used as at least one of a headlight, a day and night running light source, a tail lamp, a stop lamp, and a turn lamp.

19. The vehicle arranged to claim 17 , wherein the light emitting device is used as at least one of a headlight, a day and night running light source, a tail lamp, a stop lamp, and a turn la

Assignees

• Rohm Co Ltd

Inventors

• Nakatani Yoshiyuki
• Takagimoto Shinsuke

Classifications

• H05B45/48

  having LEDs organised in strings and incorporating parallel shunting devices · CPC title

• H02H1/0007

  concerning the detecting means (in general G01R or other subclasses of G01; reed switches H01H71/2445) · CPC title

• B60Q1/04

  the devices being headlights · CPC title

• B60Q1/34

  for indicating change of drive direction (B60Q1/22 takes precedence) · CPC title

• B60Q1/44

  for indicating braking action {or preparation for braking, e.g. by detection of the foot approaching the brake pedal} · CPC title