Drive circuit and light emitting device

Patent metadata

Field	Value
Publication number	US-11363694-B2
Application number	US-202117387633-A
Country	US
Kind code	B2
Filing date	Jul 28, 2021
Priority date	May 31, 2017
Publication date	Jun 14, 2022
Grant date	Jun 14, 2022

Abstract

A drive circuit 3 includes a power source 11; current control units 12-1 to 12-n configured to control the amount of currents supplied to a light emitting element in accordance with a pulse modulation signal; and a calculation unit 13 configured to change a duty ratio of a pulse modulation signal. The current control units 12-1 to 12-n include a first switching element 21 configured to be switched on/off in accordance with a pulse modulation signal; and a second switching element 22 configured to be switched on/off in accordance with an inversion signal of the pulse modulation signal input to the first switching element 21; and an inductor 23. The first switching element 21 and the inductor 23 are serially connected between the power source and the light emitting element. The second switching element 22 is connected between ground 25 and a contact point 24 of the first switching element 21 and the inductor 23. The two or more current control units 12-1 to 12-n are connected in parallel.

First claim

The invention claimed is:

1. A drive circuit configured to generate an output current for driving a light emitting element, comprising:
a power source;
a plurality of current control units connected to the power source in series, the plurality of current control units being connected in parallel with each other; and
a calculation unit configured to,
receive a target current value, and
output a pulse modulation signal and an inversion signal of the pulse modulation signal to the plurality of current control units in accordance with the received target current value, wherein
each of the plurality of current control units includes,
a first switching element and an inductor connected in series between the power source and the light emitting element, and
a second switching element connected between a contact point and ground, the contact point being connected to the first switching element and the inductor,

the first switching element is configured to be switched on or off in accordance with the pulse modulation signal output from the calculation unit, and the second switching element is configured to be switched on or off in accordance with the inversion signal output from the calculation unit, and
the calculation unit is configured to perform a calculation based on previously stored information to change a duty ratio of the pulse modulation signal in response to a change in the target current value received by the calculation unit.

2. The drive circuit according to claim 1 , wherein the previously stored information comprises the target current value, a voltage of the power source, a number of the plurality of current control units, an internal resistance of a current control unit among the plurality of current control units, an internal resistance of the light emitting element, and a threshold voltage due to a potential barrier of the light emitting element.

3. The drive circuit according to claim 1 , wherein the calculation unit is configured to calculate the duty ratio in accordance with Equation (1) described below, where the output current is I o , a voltage of the power source is V in , a number of the plurality of current control units is n, an internal resistance of a current control unit among the plurality of current control units is r L [k], the duty ratio that corresponds to the first switching element is D[k], an internal resistance of the light emitting element is r d , and a threshold voltage due to a potential barrier of the light emitting element is V f0

Io
=

∑

i
=
1

n

⁢

D
⁡

[
k
]

r
L

⁡

[
k
]

·

V
in

-

∑

i
=
1

n

⁢

1

r
L

⁡

[
k
]

·

V

f
⁢

⁢
0

1
+

∑

i
=
1

n

⁢

1

r
L

⁡

[
k
]

·

r
d

.

(
1
)

4. The drive circuit according to claim 1 , wherein the output current satisfies Equation (2) described below, where the output current is I o , a voltage of the power source is V in , a number of the plurality of current control units is n, an internal resistance of a current control unit among the plurality of current control units is r L [k], the duty ratio that corresponds to the first switching element is D[k], an internal resistance of the light emitting element is r d , and a threshold voltage due to a potential barrier of the light emitting element is V f0

Assignees

• Ueno Tsuyoshi
• OKA Yuuki
• Satoh Tetsuya
• Abe Seiya
• Ricoh Co Ltd
• Kyushu Inst Tech

Inventors

• Ueno Tsuyoshi
• OKA Yuuki
• Satoh Tetsuya
• Abe Seiya

Classifications

• G09G3/006

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