U.S. patent application number 15/829888 was filed with the patent office on 2018-06-07 for lighting device, luminaire, and control method for the lighting device.
The applicant listed for this patent is Panasonic Intellectual Property Management Co., Ltd.. Invention is credited to Ryuhei Hayashi, Kazuhiro Kumada, Shinichi MURAKAMI.
Application Number | 20180160495 15/829888 |
Document ID | / |
Family ID | 62163697 |
Filed Date | 2018-06-07 |
United States Patent
Application |
20180160495 |
Kind Code |
A1 |
MURAKAMI; Shinichi ; et
al. |
June 7, 2018 |
LIGHTING DEVICE, LUMINAIRE, AND CONTROL METHOD FOR THE LIGHTING
DEVICE
Abstract
A lighting device includes: a variable voltage source; a
transistor which controls a current flowing through a
light-emitting element; and a control circuit which causes the
transistor to pass a current corresponding to a received
instruction for a dimming level through the light-emitting element.
When the received instruction instructs at least a predetermined
dimming Level, the control circuit causes a voltage drop in the
transistor to become a first voltage by controlling the variable
voltage source, and when the received instruction instructs a
dimming level less than the predetermined dimming level, the
control circuit causes the voltage drop to become a second voltage
higher than the first voltage, by controlling the variable voltage
source.
Inventors: |
MURAKAMI; Shinichi; (Osaka,
JP) ; Kumada; Kazuhiro; (Hyogo, JP) ; Hayashi;
Ryuhei; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Panasonic Intellectual Property Management Co., Ltd. |
Osaka |
|
JP |
|
|
Family ID: |
62163697 |
Appl. No.: |
15/829888 |
Filed: |
December 2, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F21Y 2115/10 20160801;
H05B 45/10 20200101; H05B 45/395 20200101; H05B 45/37 20200101;
F21S 8/026 20130101; F21W 2131/406 20130101; F21V 23/001 20130101;
F21Y 2115/20 20160801; F21S 8/00 20130101 |
International
Class: |
H05B 33/08 20060101
H05B033/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 7, 2016 |
JP |
2016-238032 |
Claims
1. A lighting device which supplies power to a light-emitting
element, the lighting device comprising: a variable voltage source
which supplies a DC voltage that is variable to the light-emitting
element; a transistor which is connected in series to the
light-emitting element and controls a current flowing through the
light-emitting element; and a control circuit which receives an
instruction for a dimming level of the light-emitting element,
causes the transistor to pass a current corresponding to the
instruction received through the light-emitting element, and causes
the variable voltage source to output the DC voltage that causes a
voltage drop in the transistor to become a predetermined voltage,
wherein when the instruction received instructs at least a
predetermined dimming level, the control circuit causes the voltage
drop to become a first voltage by controlling the variable voltage
source, and when the instruction received instructs a dimming level
less than the predetermined dimming level, the control circuit
causes the voltage drop to become a second voltage higher than the
first voltage, by controlling the variable voltage source.
2. The lighting device according to claim 1, wherein the control
circuit includes a first control terminal connected to the variable
voltage source; and a second control terminal connected to the
transistor, and the control circuit: controls the variable voltage
source via the first control terminal such that the voltage drop
becomes the predetermined voltage; and causes the transistor via
the second control terminal to pass the current corresponding to
the instruction received through the light-emitting element.
3. The lighting device according to claim 1, wherein the first
voltage is a value that decreases with an increase in the dimming
level instructed by the instruction received.
4. The lighting device according to claim 3, wherein the second
voltage is a constant value independent of the dimming level
instructed by the instruction received.
5. The lighting device according to claim 1, wherein the second
voltage is a constant value independent of the dimming level
instructed by the instruction received.
6. The lighting device according to elm wherein the variable
voltage source supplies the DC voltage to a series circuit
including at least the light-emitting element and the
transistor.
7. The lighting device according to claim 1, wherein the control
circuit: monitors a voltage at a connection point between the
light-emitting element and the transistor; causes the transistor to
pass the current corresponding to the instruction received through
the light-emitting element, using the voltage at the connection
point as feedback information; and causes the voltage drop in the
transistor to become the predetermined voltage by controlling the
variable voltage source.
8. The lighting device according to claim 1, wherein the variable
voltage source is a step-down switching power supply.
9. A luminaire comprising: a light-emitting element; and the
lighting device according to claim 1 which supplies the power to
the light emitting element.
10. A lighting device which supplies power to a light-emitting
element, the lighting device comprising: a variable voltage source
which supplies a DC voltage that is variable to the light-emitting
element; a transistor which is connected in series to the
light-emitting element and controls a current flowing through the
light-emitting element; and a control circuit which receives an
instruction for a dimming level of the light-emitting element and
causes the transistor to pass a current corresponding to the
instruction received through the light-emitting element, wherein
when the instruction received instructs at least a predetermined
dimming level, the control circuit causes a voltage drop in the
transistor to become a first voltage by controlling the variable
voltage source, and when the instruction received instructs a
dimming level less than the predetermined dimming level, the
control circuit causes the voltage drop to become a second voltage
higher than the first voltage, by controlling the variable voltage
source.
11. A luminaire comprising: a light-emitting element; and the
lighting device according to claim 10 which supplies the power to
the light-emitting element.
12. A control method for a lighting device which supplies power to
a light-emitting element, the control method comprising: receiving
an instruction for a dimming level of the light-emitting element,
and causing a transistor to pass a current corresponding to the
instruction received through the light-emitting element, the
transistor being connected in series to the light-emitting element;
and causing a variable voltage source to output a DC voltage that
causes a voltage drop in the transistor to become a predetermined
voltage, the variable voltage source supplying the DC voltage that
is variable to the light-emitting element, wherein in the causing
of the variable voltage source, when the instruction received
instructs at least a predetermined dimming level, the voltage drop
is caused to become a first voltage by controlling the variable
voltage source, and when the instruction received instructs a
dimming level less than the predetermined dimming level, the
voltage drop is caused to become a second voltage higher than the
first voltage, by controlling the variable voltage source.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of priority of Japanese
Patent Application Number 2016-238032 filed on Dec. 7, 2016, the
entire content of which is hereby incorporated by reference.
BACKGROUND
1. Technical Field
[0002] The present disclosure relates to a lighting device, a
luminaire including the lighting device, and a control method for
the lighting device.
2. Description of the Related Art
[0003] For luminaires used for stage effects etc., performance
different from ordinary luminaires is demanded. The performance
referred to here is the ability to smoothly build up from a
non-lighting state by fading. Here, fading is an operation to
gradually change a brightness of a luminaire.
[0004] Various luminaires making fading possible have been
conventionally proposed (see Patent Literature (PTL) 1 (Japanese
Unexamined Patent Application Publication No. 2012-226924), for
example). The luminaire of PTL 1 smoothly adjusts a current flowing
through a light-emitting element, by intermittently stopping an
on-off operation of a switching element for use in a DC-DC
converter included in a lighting device.
SUMMARY
[0005] However, although the luminaire of PTL 1 makes ordinary
fading possible, the luminaire does not make very smooth fading
necessary for the stage effects etc. easy. This is because a
switching power supply including a step-down chopper circuit is
used in the luminaire of PTL 1, and a shift in responsiveness (a
relationship between a dimming instruction value and a brightness),
a rapid increase or decrease in light intensity during fading,
etc., occur clue to an electrolytic capacitor for anti-video
flicker included in the switching power supply.
[0006] Here, it is conceivable that in order to achieve very smooth
building up necessary for the stage effects etc., instead of a
step-down chopper circuit, a dropper circuit which makes use of a
voltage drop in a transistor is included in a lighting device. In
order to reduce heat generation by a voltage drop in the
transistor, a voltage drop (e.g., source-drain voltage Vds of an
FET) in the transistor is caused to become a constant voltage as
low as possible by controlling the lighting device including the
dropper circuit.
[0007] However, when source-drain voltage Vds is caused to stay at
an excessively low voltage by performing the controlling,
illumination light may flicker due to an influence of a variation
in drain-source voltage Vds caused by external noise. In
particular, the flicker is noticeable at a low dimming level (e.g.,
a dimming level close to the lowest limit of dimming). In other
words, the lighting device including the dropper circuit makes
reducing the heat generation in the transistor and increasing a
resistance to the flicker at the low dimming level conflict with
each other, and has difficulty managing both of them.
[0008] In view of this, the present disclosure has an object to
provide, for example, a lighting device which includes a dropper
circuit that makes very smooth fading possible, and which reduces
heat generation in the dropper circuit and the occurrence of a
flicker even at a low dimming level.
[0009] In order to achieve the above object, a lighting device
according to one aspect of the present disclosure is a lighting
device which supplies power to a light-emitting element and
includes: a variable voltage source which supplies a DC voltage
that is variable to the light-emitting element; a transistor which
is connected in series to the light-emitting element and controls a
current flowing through the light-emitting element; and a control
circuit which receives an instruction for a dimming level of the
light-emitting element, causes the transistor to pass a current
corresponding to the instruction received through the
light-emitting element, and causes the variable voltage source to
output the DC voltage that causes a voltage drop in the transistor
to become a predetermined voltage. When the instruction received
instructs at least a predetermined dimming level, the control
circuit causes the voltage drop to become a first voltage by
controlling the variable voltage source, and when the instruction
received instructs a dimming level less than the predetermined
dimming level, the control circuit causes the voltage drop to
become a second voltage higher than the first voltage, by
controlling the variable voltage source.
[0010] Moreover, in order to achieve the above object, a luminaire
according to one aspect of the present disclosure includes a
light-emitting element and the above-described lighting device
which supplies power to the light-emitting element.
[0011] Moreover, in order to achieve the above object, a control
method for a lighting device according to one aspect of the present
disclosure is a control method for a lighting device which supplies
power to a light-emitting element and includes: receiving an
instruction for a dimming level of the light-emitting element, and
causing a transistor to pass a current corresponding to the
instruction received through the light-emitting element, the
transistor being connected in series to the light-emitting element;
and causing a variable voltage source to output a DC voltage that
causes a voltage drop in the transistor to become a predetermined
voltage, the variable voltage source supplying the DC voltage that
is variable to the light-emitting element. In the causing of the
variable voltage source, when the instruction received instructs at
least a predetermined dimming level, the voltage drop is caused to
become a first voltage by controlling the variable voltage source,
and when the instruction received instructs a dimming level less
than the predetermined dimming level, the voltage drop is caused to
become a second voltage higher than the first voltage, by
controlling the variable voltage source.
[0012] The present disclosure provides a lighting device which
includes a dropper circuit making very smooth fading possible and
reduces heat generation in the dropper circuit and the occurrence
of a flicker even at a low dimming level, a luminaire including the
lighting device, and a control method for a lighting device.
BRIEF DESCRIPTION OF DRAWINGS
[0013] The figures depict one or more implementations in accordance
with the present teaching, by way of examples only, not by way of
limitations. In the figures, like reference numerals refer to the
same or similar elements.
[0014] FIG. 1 is a circuit diagram illustrating a lighting device
according to an embodiment;
[0015] FIG. 2A is a flow chart illustrating a control on a
transistor by a control circuit of the lighting device in FIG.
1;
[0016] FIG. 2B is a flow chart illustrating a control on a variable
voltage source by the control circuit of the lighting device in
FIG. 1;
[0017] FIG. 3 is a graph illustrating an example of a relationship
between a dimming level and a voltage drop in the transistor in the
control illustrated by the flow chart of FIG. 2B;
[0018] FIG. 4A is an external view illustrating an example
(downlight) of a luminaire according to the embodiment; and
[0019] FIG. 4B is an external view illustrating another example
(spotlight) of the luminaire according to the embodiment.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0020] Hereinafter, embodiments of the present disclosure will be
described in detail with reference to the drawings. It should be
noted that each of the embodiments described below shows a specific
example of the present disclosure. Therefore, numerical values,
shapes, materials, structural components, the arrangement and
connection of the structural components, steps, the sequence of the
steps, etc. shown in the following embodiments are mere examples,
and are not intended to limit the scope of the present disclosure.
Furthermore, among the structural components in the following
embodiments, structural components not recited in any one of the
independent claims which indicate the broadest concepts of the
present disclosure are described as optional structural components.
Furthermore, the figures are schematic diagrams and are not
necessarily precise illustrations. In the figures, substantially
identical components are assigned the same reference signs, and
overlapping description thereof is omitted or simplified.
[0021] FIG. 1 is a circuit diagram illustrating lighting device 10
according to an embodiment.
[0022] Lighting device 10 is a device which supplies power to
light-emitting element 5, and is a power circuit which makes use of
a dropper circuit (a voltage drop in transistor Q2). Lighting
device 10 includes input circuit 11, rectifier circuit 12, power
factor correction (PFC) circuit 13, smoothing circuit 14, variable
voltage source 15, transistor Q2, resistor R1, and id control
circuit 16. It should be noted that FIG. 1 also illustrates
light-emitting element 5 and dimmer 6 connected to lighting device
10.
[0023] Light-emitting element 5 is an element which emits
illumination light in response to supply of current, and is, for
example, a light-emitting diode (LED).
[0024] Dimmer 6 is a device which outputs, to lighting device 10
(more specifically control circuit 16), a dimming signal
instructing a dimming level. Dimmer 6 includes, for example, an
input device such as a dial, a slider, an operation button, and a
touch panel, a detection circuit which reads an instruction from
the input device, and a signal generation/output/communication
circuit which outputs the instruction as a dimming signal via a
wired or wireless connection.
[0025] Input circuit 11 is a circuit which receives
alternating-current (AC) power, and includes, for example, a
connector connected to a commercial power source, a power filter,
and so on.
[0026] Rectifier circuit 12 is a circuit which converts AC power
into direct-current (DC) power, and includes a bridge diode and so
on.
[0027] PFC circuit 13 is, for example, a DC-DC converter.
[0028] Smoothing circuit 14 is a circuit which smoothes a pulsating
voltage/current into a voltage/current similar to a DC
voltage/current, and includes, for example, a capacitor, a choke
coil, and so on.
[0029] Variable voltage source 15 is a power source which supplies
a variable DC voltage to light-emitting element 5, and steps down a
DC voltage outputted from smoothing circuit 14 to a DC voltage
corresponding to a control signal received from first control
terminal 16a of control circuit 16, and outputs the stepped-down DC
voltage. The outputted DC voltage is applied to light-emitting
element 5, transistor Q2, and resistor R1 that are connected in
series.
[0030] More specifically, variable voltage source 15 is a step-down
switching power supply including diode D1, inductor L1, capacitor
C1, and transistor Q1. Transistor Q1 is turned on and off as a
switching element according to a control signal received from first
control terminal 16a of control circuit 16. When transistor Q1 is
turned on, inductor L1 stores energy as a current flows through
inductor L1. When transistor Q1 is turned off, inductor L1
generates an electromotive force, and a current flows through
inductor L via diode D1. In this manner, capacitor C1 smoothes the
current flowing through inductor L1, and variable voltage source 15
outputs a DC voltage.
[0031] Transistor Q2 is a transistor which is connected in series
to light-emitting element 5 and controls a current flowing through
light-emitting element 5, and is, for example, an n-channel MOS
FET. Transistor Q2 also serves as a dropper circuit which steps
down a voltage that variable voltage source 15 applies to a load
(light-emitting element 5) by a voltage drop generated (a
drain-source voltage).
[0032] Resistor R1 is a resistor for protection, and is, for
example, a resistance element having a small resistance value.
[0033] Control circuit 16 is a circuit which controls variable
voltage source 15 and transistor Q2 based on a dimming signal from
dimmer 6, and is achieved by, for example, a microcomputer. The
microcomputer is a one-chip semiconductor integrated circuit
including a read-only memory (ROM) which stores a program, a
random-access memory (RAM), a processor (CPU) which executes a
program, a timer, and an input-output circuit such as an A/D
converter and a D/A converter.
[0034] More specifically, when receiving an instruction (dimming
signal) for a dimming level of light-emitting element 5 from dimmer
6, control circuit 16 performs the following two controls.
Specifically, transistor Q2 is caused to pass a current
corresponding to the received instruction through light-emitting
element 5. Variable voltage source 15 is caused to output a DC
voltage which causes a drop voltage in transistor Q2 to become a
predetermined voltage. Specifically, when the instruction received
from dimmer 6 instructs at least a predetermined dimming level,
control circuit 16 causes the drop voltage in transistor Q2 to
become a first voltage by controlling variable voltage source 15.
In contrast, when the instruction received from dimmer 6 instructs
dimming level less than the predetermined dimming level, control
circuit 16 causes the drop voltage in transistor Q2 to become a
second voltage by controlling variable voltage source 15.
[0035] Control circuit 16 includes: first control terminal 16a
connected to a control terminal (gate) of transistor Q1 of variable
voltage source 15; and second control terminal 16b connected to a
control terminal (gate) of transistor Q2. Control circuit 16 causes
the voltage drop in transistor Q2 to become a predetermined voltage
by controlling variable voltage source 15 via first control
terminal 16a. On the other hand, control circuit 16 causes
transistor Q2 via second control terminal 16b to pass the current
corresponding to the instruction (dimming signal) from dimmer 6
through light-emitting element 5.
[0036] Next, operations performed by lighting device 10 according
to the embodiment which is thus configured will be described. In
what follows, operations performed by control circuit 16 receiving
an instruction (dimming signal) from dimmer 6 will be mainly
described.
[0037] When receiving an instruction (dimming signal) for a dimming
level of light-emitting element 5 from dimmer 6, control circuit 16
performs the following two controls in parallel (or sequentially).
Specifically, transistor Q2 is caused to pass a current
corresponding to the instruction received through light-emitting
element 5. Variable voltage source 15 is caused to output a DC
voltage which causes a drop voltage in transistor Q2 to become a
predetermined voltage.
[0038] FIG. 2A is a flow chart illustrating a control (i.e., a
dimming step) on transistor Q2 by control circuit 16 of lighting
device 10.
[0039] When receiving an instruction (dimming signal) for a dimming
level of dimmer 6 (S10), control circuit 16 causes transistor Q2
via second control terminal 16b to pass a current corresponding to
the instruction (dimming signal) from dimmer 6 through
light-emitting element 5 (S11).
[0040] Specifically, control circuit 16 stores a correspondence
table for instructions from dimmer 6 and voltages to be applied to
the control terminal (gate) of transistor Q2, and applies a voltage
corresponding to the instruction from dimmer 6 to the control
terminal (gate) of transistor Q2 by reference to the correspondence
table. It should be noted that by monitoring a voltage at a
connection point between transistor Q2 and resistor R1 and
performing a feedback control such that the voltage becomes
constant, control circuit 16 may perform a constant current control
such that a current flowing through resistor R1, that is, a current
flowing through light-emitting element 5, becomes constant.
[0041] With such a control illustrated in FIG. 2A, the current
corresponding to the instruction from dimmer 6 flows through
light-emitting element 5, and a dimming control is performed.
[0042] FIG. 2B is a flow chart illustrating a control (i.e., a
voltage control step) on variable voltage source 15 by control
circuit 16 of lighting device 10.
[0043] When receiving an instruction (dimming signal) for a dimming
level from dimmer 6 (S20), control circuit 16 determines whether
the instruction instructs at least a predetermined dimming level
(S21).
[0044] When the instruction from dimmer 6 is determined to instruct
at least the predetermined dimming level (YES in S21), control
circuit 16 causes a voltage drop in transistor Q2 to become a
predetermined first voltage by controlling variable voltage source
15 via first control terminal 16a (S22).
[0045] More specifically, control circuit 16 monitors, as the
voltage drop in transistor Q2, a voltage at a connection point
between light-emitting element 5 an transistor Q2, and performs a
feedback control on transistor Q1 such that the voltage becomes a
first voltage. The control on transistor Q1 is performed by, for
example, changing a duty cycle of a PWM signal provided to
transistor Q1, that is, changing on time in a single on-off cycle
in which transistor Q1 is turned on and off.
[0046] It should be noted that the voltage at the connection point
between light-emitting element 5 and transistor Q2 is strictly the
sum of the voltage drop in transistor Q2 and a voltage drop in
resistor R1. However, because the resistance value of resistor R1
is small, in the embodiment, control circuit 16 performs the
control, assuming that the voltage at the connection point between
light-emitting element 5 and transistor Q2 is the voltage drop in
transistor Q2.
[0047] In contrast, when the instruction from dimmer 6 instructs a
dimming level less than the predetermined dimming level (NO in
S21), control circuit 16 causes a drop voltage in transistor Q2 to
become a predetermined second voltage higher than the first
voltage, by controlling variable voltage source 15 via first
control terminal 16a (S23). Specifically, control circuit 16
monitors, as the voltage drop in transistor Q2, a voltage at the
connection point between light-emitting element 5 and transistor
Q2, and performs a feedback control such that the voltage becomes
the second voltage.
[0048] FIG. 3 is a graph illustrating an example of a relationship
between an instruction from dimmer 6 ("dimming level" indicated by
the horizontal axis) and a voltage drop in transistor Q2
("drain-source voltage Vds" indicated by the vertical axis) in the
control illustrated by the flow chart of FIG. 2B.
[0049] In this example, when the instruction from dimmer 6
instructs at least the predetermined dimming level (20%), control
circuit 16 causes drain-source voltage Vds of transistor Q2 to
become the first voltage by controlling voltage variable voltage
source 15 via first control terminal 16a. As illustrated in the
graph, the first voltage is a downward-sloping voltage that
decreases with an increase in dimming level. Specifically,
drain-source voltage Vds becomes 10V when the dimming level is 20%;
decreases with the increase in dimming level; and becomes 2V when
the dimming level is 100%. Accordingly, in the case of at least the
predetermined dimming level that may cause problematic heat
generation by a large current flowing through light-emitting
element 5, the voltage drop in transistor Q2 is maintained at the
first voltage that is relatively low.
[0050] In contrast, when the instruction from dimmer 6 instructs a
dimming level less than the predetermined dimming level (20%),
control circuit 16 causes the voltage drop in transistor Q2 to
become the predetermined second voltage (10V) higher than the first
voltage, by controlling variable voltage source 15 via first
control terminal 16a. Here, the second voltage is a constant value
(10V) independent of a dimming level. Accordingly, in the case of
the dimming level less than the predetermined dimming level that
causes no problematic heat generation, the voltage drop in
transistor Q2 is maintained at the second voltage that is
relatively high and less likely to be influenced by external noise
(i.e., less likely to cause a flicker).
[0051] It should be noted that a value (%) of a dimming level
corresponds to a brightness. For example, full illumination (the
maximum brightness) is indicated by 100%, and a non-illumination
state is indicated by 0%.
[0052] With such a control illustrated in FIG. 2B and FIG. 3, the
voltage drop in transistor Q2 is controlled according to the
instruction from dimmer 6, the heat generation in the dropper
circuit (transistor Q2) is reduced, and the occurrence of the
flicker is reduced even at the low dimming level.
[0053] As described above, lighting device 10 according to the
embodiment is a lighting device which supplies power to
light-emitting element 5 and includes: variable voltage source 15
which supplies a DC voltage that is variable to light-emitting
element 5; transistor Q2 which is connected in series to
light-emitting element 5 and controls a current flowing through
light-emitting element 5; and control circuit 16 which receives an
instruction for a dimming level of light-emitting element 5, causes
transistor Q2 to pass a current corresponding to the instruction
received through light-emitting element 5, and causes variable
voltage source 15 to output the DC voltage that causes a voltage
drop in transistor Q2 to become a predetermined voltage. When the
received instruction instructs at least a predetermined dimming
level, control circuit 16 causes the voltage drop to become a first
voltage by controlling variable voltage source 15, and when the
received instruction instructs a dimming level less than the
predetermined dimming level, control circuit 16 causes the voltage
drop to become a second voltage higher than the first voltage, by
controlling variable voltage source 15.
[0054] With this, in lighting device 10 including the dropper
circuit, in the case of at least the predetermined dimming level
that may cause problematic heat generation by a large current
flowing through light-emitting element 5, the voltage drop in
transistor Q2 is maintained at the first voltage that is relatively
low. In contrast, in the case of the dimming level less than the
predetermined dimming level that causes no problematic heat
generation, the voltage drop in transistor is maintained at the
second voltage that is relatively high and less likely to be
influenced by external noise. Accordingly, the lighting device is
achieved which includes the dropper circuit that makes very smooth
fading necessary for the stage effects etc. possible, and reduces
the heat generation in the dropper circuit and the occurrence of a
flicker even at the low dimming level.
[0055] Moreover, control circuit 16 includes first control terminal
16a connected to variable voltage source 15; and second control
terminal 16b connected to transistor Q2. In addition, control
circuit 16: controls variable voltage source 15 via first control
terminal 16a such that the voltage drop becomes the predetermined
voltage; and causes transistor Q2 via second control terminal 16b
to pass the current corresponding to the instruction received
through light-emitting element 5.
[0056] With this, control circuit 16 may control variable voltage
source 15 via one of the two control terminals, and transistor Q2
via the other of the two control terminals. Accordingly, the simple
control reduces the heat generation in the dropper circuit and the
occurrence of the flicker at the low dimming level.
[0057] Moreover, the first voltage is a value that decreases with
an increase in the dimming level instructed by the instruction
received.
[0058] With this, the voltage drop in transistor Q2 is caused to
decrease with an increase in a current flowing through transistor
Q2 via light-emitting element 5. As a result, an increase in the
heat generation in transistor Q2 when the dimming level is high is
reduced.
[0059] Moreover, the second voltage is a constant value independent
of the dimming level instructed by the instruction received.
[0060] With this, when a current flowing through transistor Q2 via
light-emitting element 5 is low, the voltage drop in transistor Q2
may be maintained constant independent of the current flowing
through transistor Q2. As a result, the control on transistor Q2 is
simplified.
[0061] Moreover, a control method for lighting device 10 according
to the embodiment is a method for supplying power to light-emitting
element 5, the method including: receiving an instruction for a
dimming level of light-emitting element 5, and causing transistor
Q2 to pass a current corresponding to the instruction received
through light-emitting element 5, transistor Q2 being connected in
series to light-emitting element 5; and causing variable voltage
source 15 to output a DC voltage that causes a voltage drop in
transistor Q2 to become a predetermined voltage, variable voltage
source 15 supplying the DC voltage that is variable to
light-emitting element 5. In the causing of variable voltage source
15, when the instruction received instructs at least a
predetermined dimming level, the voltage drop is caused to become a
first voltage by controlling variable voltage source 15, and when
the instruction received instructs a dimming level less than the
predetermined dimming level, the voltage drop is caused to become a
second voltage higher than the first voltage, by controlling
variable voltage source 15.
[0062] With this, in lighting device 10 including the dropper
circuit, in the case of at least the predetermined dimming level
that may cause problematic heat generation by a large current
flowing through light-emitting element 5, the voltage drop in
transistor Q2 is maintained at the first voltage that is relatively
low. In contrast, in the case of the dimming level less than the
predetermined dimming level that causes no problematic heat
generation, the voltage drop in transistor Q2 is maintained at the
second voltage that is relatively high and less likely to be
influenced by external noise. Accordingly, the lighting device is
achieved which includes the dropper circuit that makes very smooth
fading necessary for the stage effects etc. possible, and reduces
the heat generation in the dropper circuit and the occurrence of a
flicker even at the low dimming level.
[0063] FIG. 4A and FIG. 4B are external views of luminaires 20a and
20b according to the embodiment, respectively.
[0064] Luminaire 20a illustrated in FIG. 4A is a downlight used for
the stage effects etc., and includes circuit box 21a, lamp body
22a, and wire 23. Circuit box 21a is a metal box which houses
lighting device 10 (not shown) according to the embodiment. Lamp
body 22a is a fixture to which an LED (not shown) that is
light-emitting element 5 is attached and which is fixed by being
embedded in a ceiling etc. Wire 23 is a cable which electrically
connects lighting device 10 in circuit box 21a and the LED in lamp
body 22a.
[0065] Luminaire 20b illustrated in FIG. 4B is a spotlight used for
the stage effects etc., and includes circuit box 21b and lamp body
22b. Circuit box 21b is a metal box which houses lighting device 10
(not shown) according to the embodiment and is attached to a
dedicated rail etc. Lamp body 22b is a fixture to which an LED (not
shown) that is light-emitting element 5 is attached.
[0066] Such luminaires 20a and 20b each include light-emitting
element 5 and lighting device 10 according to the embodiment which
supplies power to light-emitting element 5.
[0067] With this, in lighting device 10 included in each of
luminaires 20a and 20b, the dropper circuit is used, and in the
case of at least the predetermined g level that may cause
problematic heat generation by a large current flowing through
light-emitting element 5, the voltage drop in transistor Q2 is
maintained at the first voltage that is relatively low. In
contrast, in the case of the dimming level less than the
predetermined dimming level that causes no problematic heat
generation, the voltage drop in transistor Q2 is maintained at the
second voltage that is relatively high and less likely to be
influenced by external noise. Accordingly, the luminaire is
achieved which includes the lighting device that makes very smooth
fading necessary for the stage effects etc. possible, and which
reduces the heat generation in the dropper circuit and the
occurrence of a flicker even at the low dimming level.
[0068] Although lighting device 10 and luminaires 20a and 20b
according to the present disclosure have been described based on
the embodiment, the present disclosure is not limited to the
embodiment. Forms obtained by various modifications to the
embodiment that can be conceived by a person skilled in the art as
well as other forms realized by optionally combining some of the
structural components in the embodiment which are within the scope
of the essence of the present disclosure are included in the
present disclosure.
[0069] For example, although light-emitting element 5 is the LED in
the aforementioned embodiment, the present disclosure is not
limited to this. Another light-emitting element such as an organic
electroluminescence (EL) element may be the LED.
[0070] Moreover, although lighting device 10 includes input circuit
11, rectifier circuit 12, PFC circuit 13, and smoothing circuit 14
in the aforementioned embodiment, these circuits may be optional.
Lighting device 10 may be, for example, a power circuit which
includes none of the circuits arid receives DC voltage from a
battery.
[0071] Moreover, although variable voltage source 15 is the
step-down switching power supply in the aforementioned embodiment,
the present disclosure is not limited to this. Variable voltage
source 15 may be any voltage source such as a linear regulator as
long as the voltage source is a DC voltage source capable of
changing an output voltage according to an external control
signal.
[0072] Moreover, although resistor R1 for protection is used in
lighting device 10 in the aforementioned embodiment, resistor R1 is
optional and may not be omitted depending on required
specifications.
[0073] Moreover, control circuit 16 is implemented through software
by a microcomputer having a program in the aforementioned
embodiment. However, the implementation method is not limited to
such, and control circuit 16 may be implemented through hardware by
a dedicated electronic circuit including an A/D converter, a logic
circuit, a gate array, a D/A converter, etc.
[0074] Moreover, the first voltage used in control circuit 16 is a
value that decreases with the increase in dimming level in the
aforementioned embodiment. However, the first voltage is not
limited to this, and may be a voltage that stays constant
independent of a dimming level, a voltage that decreases in a
staircase pattern with the increase in dimming level, a voltage
that curvilinearly decreases with the increase in dimming level, or
the like, as long as any of these voltages is lower than the second
voltage.
[0075] Moreover, the second voltage used in control circuit 16 is a
constant voltage independent of a dimming level in the
aforementioned embodiment. However, the second voltage is not
limited to this, and may be a value that decreases with the
increase in dimming level, like the first voltage, as long as the
value is a voltage higher than the first voltage.
[0076] Moreover, although luminaires 20a and 20b are the downlight
and the spotlight, respectively, in the aforementioned embodiment,
luminaires 20a and 20b are not limited to these types, and may be
other types of luminaire such as a ceiling light, a chandelier, a
pendant light, and a flat light.
[0077] While the foregoing has described one or more embodiments
and/or other examples, it is understood that various modifications
may be made therein and that the subject matter disclosed herein
may be implemented in various forms and examples, and that they may
be applied in numerous applications, only some of which have been
described herein. It is intended by the following claims to claim
any and all modifications and variations that fall within the true
scope of the present teachings.
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