# US 10,375,783 B2 · Lighting circuit and vehicular lamp

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- Number: US 10,375,783 B2
- Document ID: US10375783B2
- Status: Granted
- Kind: B2
- Application number: 15/659,937
- Filed: 2017-07-26
- Published: 2018-02-15
- Granted: 2019-08-06
- Earliest claimed: 2016-08-10
- Assignees: Koito Manufacturing Co., Ltd.
- Applicants: Koito Manufacturing Co., Ltd.
- Inventors: Kotaro Matsui; Yasushi Noyori; Shinji Ohta
- Web page: https://patentgrep.com/patent/US10375783B2

## CPC

- H05B 45/30: Driver circuits
- B60Q 1/1407: {General lighting circuits comprising dimming circuits}
- H05B 45/44: with an active control inside an LED matrix
- H05B 45/46: having LEDs disposed in parallel lines
- H05B 45/48: having LEDs organised in strings and incorporating parallel shunting devices
- H05B 45/10: Controlling the intensity of the light
- H05B 47/10: Controlling the light source
- H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- B60Q: ARRANGEMENT OF SIGNALLING OR LIGHTING DEVICES, THE MOUNTING OR SUPPORTING THEREOF OR CIRCUITS THEREFOR, FOR VEHICLES IN GENERAL

## Abstract

Provided is a lighting circuit that drives a first light source and a second light source connected in series with each other. A bypass switch is provided in parallel with the second light source. A constant current circuit is connected in parallel with one of the first light source and the second light source. A drive circuit supplies a drive current to a serially-connected circuit of the first light source and the second light source.

## Claims

### Claim 1

A lighting circuit comprising:
a first light source;
a second light source connected in series with the first light source to form a serially-connected circuit;
a bypass switch provided in parallel with the second light source;
a constant current circuit connected in parallel with only one of the first light source or the second light source at a time and configured to generate a constant current; and
a drive circuit configured to supply a drive current to the serially-connected circuit including the first light source and the second light source,
wherein the drive circuit is only directly connected to an input of the first light source of the serially-connected circuit including the first light source and the second light source.

### Claim 2 (depends on 1)

The lighting circuit of claim 1, wherein the constant current circuit is provided in parallel with the second light source and in parallel with the bypass switch.

### Claim 3 (depends on 1)

The lighting circuit of claim 1, wherein the constant current circuit is provided in parallel with the first light source.

### Claim 4 (depends on 3)

The lighting circuit of claim 3, wherein on/off of a current of the constant current circuit is configured to be switchable.

### Claim 5 (depends on 4)

The lighting circuit of claim 4, wherein the on/off of the current of the constant current circuit is switchable in association with the bypass switch.

### Claim 6 (depends on 5)

The lighting circuit of claim 5, wherein the on/off of the current of the constant current circuit is controlled complementarily with on/off of the bypass switch.

### Claim 7 (depends on 4)

The lighting circuit of claim 4, further comprising:
a current control switch connected in series with the constant current circuit so as to form a path that is in parallel with the first light source.

### Claim 8 (depends on 5)

The lighting circuit of claim 5, further comprising:
a current control switch connected in series with the constant current circuit so as to form a path that is in parallel with the first light source.

### Claim 9 (depends on 1)

A vehicular lamp comprising:
the lighting circuit of claim 1 that drives the first light source and the second light source.

### Claim 10 (depends on 1)

The lighting circuit of claim 1, further comprising:
a switch driver configured to turn off the bypass switch when an input terminal is at a high level, and turn on the bypass switch when the input terminal is at a low level.

### Claim 11 (depends on 1)

The lighting circuit of claim 1, wherein components having different rated currents are selected for the first light source and the second light source, respectively.

### Claim 12 (depends on 1)

The lighting circuit of claim 1, wherein the drive circuit is a constant voltage output converter.

### Claim 13 (depends on 2)

The lighting circuit of claim 2, wherein the constant current circuit only generates constant current when the bypass switch is turned off.

### Claim 14 (depends on 3)

The lighting circuit of claim 3, wherein the constant current circuit only generates constant current when the bypass switch is turned on.