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AssigneeRohm Co., Ltd.
InventorsYoshiyuki Nakatani, Shinsuke Takagimoto
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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.
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:
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:
Dependencies are inferred from the claim text.
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Responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits: in a series array of LEDs
The devices being primarily intended to illuminate the way ahead or to illuminate other areas of way or environments: the devices being headlights
The devices being primarily intended to indicate the vehicle, or parts thereof, or to give signals, to other traffic: for indicating change of…
The devices being primarily intended to indicate the vehicle, or parts thereof, or to give signals, to other traffic: for indicating braking…
About 10 years 6 months of term left · ends 28 Apr 2037 (estimated)
This nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2016-094818 filed in Japan on May 10, 2016, the entire contents of which are hereby incorporated by reference.
The present invention relates to a ground fault detection circuit, and an abnormality detection circuit, a light emitting device, and a vehicle each using the ground fault detection circuit.
A light emitting device including a series connection unit constituted of a plurality of light emitting diodes is used as a headlight of a vehicle, for example. When it is used as a headlight of a vehicle, in order to realize an adaptive front-lighting system (AFS) or an adaptive driving beam (ADB), it is preferred to adopt a structure in which short-circuit switches are disposed and respectively connected in parallel to light emitting elements of the series connection unit, so that the number of lighted light emitting diodes can be controlled by turning on and off the short-circuit switches.
FIG. 1 is a diagram illustrating a first structural example of a light emitting device.
FIG. 2 is a diagram illustrating a second structural example of the light emitting device.
FIG. 3 is a diagram illustrating a third structural example of the light emitting device.
FIG. 1 is a diagram illustrating a first structural example of a light emitting device. The light emitting device illustrated in FIG. 1 includes a series connection unit constituted of eight light emitting diodes D1 to D8, a driving circuit 1 that drives the light emitting diodes D1 to D8, and a lighted element number control IC (integrated circuit) 2 that controls the number of lighted elements in the light emitting diodes D1 to D8. The lighted element number control IC 2 includes N-channel MOS field-effect transistors Q1 to Q8, a control logic circuit 3 that controls on and off of the transistors Q1 to Q8 in accordance with a lighted element number indicating signal S1 supplied externally, short-circuit detection circuits 4A to 4H, an OR gate 5, a comparator 6, and a reference voltage source 7. Note that, in the structural example of FIG. 1, the number of the light emitting diodes, the number of the transistors as short-circuit switches, and the number of the short-circuit detection circuits are each eight, but the number may be two or more without limiting to eight.
The driving circuit 1 is, for example, a series regulator that supplies a constant current to a load connected to its output terminal, a switching regulator that supplies a pulse width modulated (PWM) current having a predetermined on-duty to a load connected to its output terminal, or the like.
The anode of the series connection unit constituted of the light emitting diodes D1 to D8 (anode of the light emitting diode D1) is connected to the output terminal of the driving circuit 1. The cathode of the series connection unit constituted of the light emitting diodes D1 to D8 (cathode of the light emitting diode D8) is connected to the ground.