JP7189598B2 - lighting equipment - Google Patents

Description

The present invention relates to a lighting device using LEDs (Light Emitting Diodes).

In recent years, stage lighting and production lighting using three primary color (RGB) LEDs have become widespread. The three primary color LEDs are connected to a controller (for example, an operator console, a PC, etc.) via a cable conforming to the DMX512 standard, for example, and are dimmed and controlled by the controller for each color at arbitrary timing (see, for example, Patent Document 1).

As a method of driving the three primary color LEDs, a DC/DC converter with constant current output is connected to each LED of each color, and each DC/DC converter is PWM (Pulse Width Modulation) controlled to individually dim and control the LEDs of each color. We can think of a way to do this.

JP 2003-264090 A

In the driving method described above, starting and stopping of the DC/DC converter are frequently repeated. Turning on/off the output of this DC/DC converter generates a large amount of noise. Audible noise may also occur.

Also, if a DC/DC converter is installed for each LED of each color, three DC/DC converters are required, which increases the installation space of the DC/DC converters. Also, the cost of the DC/DC converter increases.

Also, the circuit board on which the three primary color LEDs are mounted is designed on the basis of heat dissipation when all the three LEDs are lit. Normally, a DC/DC converter that drives an LED of a certain color does not know the lighting state of LEDs of other colors. driving the LED. Therefore, when the LEDs of other colors are turned off, the LEDs are driven with power lower than the allowable power of the circuit board.

The present invention has been made in view of such circumstances, and its object is to fully exhibit the capabilities of LEDs with a small circuit area and low noise in a lighting device having a plurality of LEDs connected in parallel. To provide a lighting device capable of

In order to solve the above problems, a lighting device according to one aspect of the present invention includes: a plurality of LEDs connected in parallel; a plurality of first switches connected in series to the plurality of LEDs; a first control circuit for individually controlling the plurality of first switches based on an optical signal; a dummy load connected in parallel with the plurality of LEDs; and a second switch connected in series with the dummy load. a DC/DC converter that converts an input DC voltage and outputs constant-current DC power to a power supply line in which the plurality of LEDs and the dummy load are connected in parallel; and the plurality of first switches. monitoring a plurality of signals for controlling on/off, outputting a signal for controlling the second switch to be off when at least one of the plurality of signals includes an on signal, and outputting a signal for controlling the second switch to be off, all of the plurality of signals and a second control circuit that outputs a signal for controlling the second switch to be ON when is an OFF signal.

Any combination of the above constituent elements, and conversion of expressions of the present invention between devices, methods, systems, etc. are also effective as aspects of the present invention.

Advantageous Effects of Invention According to the present invention, in a lighting device having a plurality of LEDs connected in parallel, it is possible to fully exhibit the performance of the LEDs with a small circuit area and low noise.

It is a figure which shows the circuit structure of the illuminating device which concerns on a comparative example. It is a figure which shows the circuit structure of the illuminating device which concerns on embodiment of this invention. 4 is a diagram summarizing the ON/OFF relationship of a red switch, a green switch, and a blue switch controlled by a first control circuit, and a dummy load switch controlled by a second control circuit; FIG.

FIG. 1 is a diagram showing a circuit configuration of a lighting device 1 according to a comparative example. The illumination device 1 is a full-color illumination device including three primary color LEDs (specifically, a red LED 20R, a green LED 20G, and a blue LED 20B). A DC power supply and a dimming signal are supplied to the lighting device 1 from the outside. In the example shown in FIG. 1, a DC voltage of 24 V is supplied from the outside through two wires, a power supply line and a ground line. The power line is connected to the power terminal VIN of the lighting device 1 , and the ground line is connected to the ground terminal GND of the lighting device 1 . Also, a dimming signal is supplied from the outside through the control signal line. The transmission side of the control signal line is connected to a dimming controller (for example, an operator console, PC, etc.), and the receiving side of the control signal line is connected to the dimming terminal DIM of the illumination device 1 . A dimming signal conforming to, for example, the DMX512 standard is supplied to the lighting device 1 from the dimming controller.

In the lighting device 1, a fuse F1 and a first diode D1 are inserted in the input stage of a power supply line (24V DC line in the example shown in FIG. 1) connected to the power supply terminal VIN. The fuse F1 is fused when a current exceeding the rated value flows through the power supply line (24V line), and protects the components in the lighting device 1 from overcurrent. A polyswitch may be used instead of the fuse F1. The first diode D1 is a reverse-connection prevention diode that is connected in such a direction that the power supply terminal VIN side becomes an anode. When an operator or user mistakenly connects the ground wire to the power terminal VIN of the lighting device 1 and the power wire to the ground terminal GND, the reverse current does not flow in the lighting device 1 .

The DC/DC converter 11 is a step-down constant current DC/DC converter. A power supply line (24V line) is connected to the input terminal VIN of the DC/DC converter 11 . A power supply line W1 connected to a load is connected to an output terminal SW of the DC/DC converter 11 . The main loads in FIG. 1 are the red LED 20R, the green LED 20G and the blue LED 20B connected in parallel.

A current detection terminal CS of the DC/DC converter 11 receives a voltage for detecting the current flowing through the load (that is, the output current of the DC/DC converter 11). More specifically, a divided voltage between the load and the fifth resistor R5 connected in series is input. A fifth resistor R5 is a sensing resistor for detecting the current flowing through the load.

The DC/DC converter 11 internally includes switches, drivers, comparators, and error amplifiers as main components. The switch is connected in the wiring between the input terminal VIN and the output terminal SW. For example, a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) can be used for the switch. The error amplifier amplifies the error between a predetermined reference voltage and the voltage input to the current detection terminal CS to generate an error signal. The comparator compares a predetermined carrier wave (triangular wave) signal and an error signal input from the error amplifier to generate a PWM signal. The driver controls on/off of the switch according to the PWM signal input from the comparator.

When the output current of the DC/DC converter 11 monitored by the voltage input to the current detection terminal CS becomes lower than the target value, the DC/DC converter 11 controls to increase the duty ratio of the switch, and the output current becomes higher than the target value, the duty ratio of the switch is controlled to be lowered. With such current feedback control, the current output from the output terminal SW of the DC/DC converter 11 is maintained at the target value.

An output filter is connected to the output terminal SW of the DC/DC converter 11 . In the example shown in FIG. 1, the output filter is composed of an LC filter. Specifically, an inductor L1 is inserted in the power supply line W1 connected to the output terminal SW of the DC/DC converter 11 . A capacitor C1 is connected between the power supply line W1 and the ground line. Capacitor C1 is connected to the output side of inductor L1.

A second diode D2 is connected between the power supply line W1 and the ground line. The second diode D2 is a commutation diode (free wheel diode) connected in such a direction that the anode is on the ground line side and the cathode is on the power supply line W1 side. A second diode D2 is connected to the input side of the inductor L1. The second diode D2 commutates the energy stored in the inductor L1 to the load while the switch in the DC/DC converter 11 is off.

A first resistor R1, a red LED 20R, and a red switch S1r are connected in series between a power supply line W1 (high side line) and a low side line W2. A second resistor R2, a green LED 20G, and a green switch S1g are connected in series between the power supply line W1 and the low side line W2. A third resistor R3, a blue LED 20B, and a blue switch S1b are connected in series between the power supply line W1 and the low-side line W2.

The low side line W2 is connected to the ground potential via the fifth resistor R5. The voltage of the low side line W2 is input to the current detection terminal CS of the DC/DC converter 11 as described above.

In the example shown in FIG. 1, N-channel MOSFETs are used for the red switch S1r, the green switch S1g, and the blue switch S1b. Specifically, the source terminals of the red switch S1r, the green switch S1g, and the blue switch S1b are commonly connected to the low side line W2, and the drain terminals are the cathode terminal of the red LED 20R, the cathode terminal of the green LED 20G, and the blue LED 20G. They are connected to the cathode terminals of the LEDs 20B, respectively. A drive signal defined by a PWM signal is input from the first control circuit 12 to each gate terminal of the switch S1r for red, the switch S1g for green, and the switch S1b for blue.

The first control circuit 12 receives dimming signals for the red LED 20R, the green LED 20G, and the blue LED 20B that are input from the dimming terminal DIM, and switches the red switch S1r, the green switch S1g, and the blue switch S1g according to the received dimming signal. A PWM signal is generated to be supplied to each switch S1b. In the example shown in FIG. 1, the first control circuit 12 is composed of a DMX decoder IC.

Note that the dimming signal may be given in a data format other than the DMX format. If the dimming signal is given in a data format other than the DMX format, the first control circuit 12 is composed of a microcontroller or another logic IC corresponding to the data format.

The first control circuit 12 applies a high-level voltage (on signal) to the gate terminal of the red switch S1r to turn on the red switch S1r and turn on the red LED 20R. Further, the first control circuit 12 can turn off the red switch S1r and turn off the red LED 20R by applying a low level voltage (off signal) to the gate terminal of the red switch S1r. Also, the first control circuit 12 can adjust the light amount of the red LED 20R by controlling the duty ratio of the high level and the low level.

Similarly, the first control circuit 12 can control the ON/OFF of the green LED 20G and the amount of light by controlling the ON/OFF of the green switch S1g. Similarly, the first control circuit 12 can control the ON/OFF of the blue LED 20B and the amount of light by controlling the ON/OFF of the blue switch S1b.

In this manner, the first control circuit 12 can individually PWM-control the red LED 20R, the green LED 20G, and the blue LED 20B. Therefore, the first control circuit 12 can simultaneously turn on three of the red LED 20R, the green LED 20G and the blue LED 20B, or turn on two of them at the same time, or turn on only one of them. It can also be lit. It is also possible to change the amount of light of two or three LEDs that are lit at the same time. This makes it possible to obtain an arbitrary emission color.

A first resistor R1 connected to the anode terminal of the red LED 20R, a second resistor R2 connected to the anode terminal of the green LED 20G, and a third resistor R3 connected to the anode terminal of the blue LED 20B equalize the current flowing through each LED. It is a balance resistor to make The forward voltage drop Vf of the LED varies depending on the color of emitted light. Generally, a red LED is about 1.8 to 2.2V, a green LED is about 2.2 to 3.7V, and a blue LED is about 3.2 to 3.7V.

The first resistor R1, the second resistor R2, and the third resistor R3 are designed to equalize the load of the three series circuits in which the red LED 20R, the green LED 20G, and the blue LED 20B, each having a different forward voltage drop Vf, are connected. be done. For example, the resistance value of the first resistor R1 is set higher than the resistance value of the third resistor R3. The load on each column can be adjusted by changing the number of resistance elements connected to each column.

In the example shown in FIG. 1, the DC/DC converter 11 continues to output constant-current DC power regardless of the ON/OFF states of the switch S1r for red, the switch S1g for green, and the switch S1b for blue. When the red switch S1r, the green switch S1g, and the blue switch S1b are all turned on, the output current of the DC/DC converter 11 is evenly divided into three lines. In addition, in a state in which two of the switch S1r for red, the switch S1g for green, and the switch S1b for blue are turned on, the output current of the DC/DC converter 11 is evenly split between the two lines that are turned on. When any one of the red switch S1r, the green switch S1g, and the blue switch S1b is turned on, the output current of the DC/DC converter 11 all flows through the one row that is turned on.

In any state, the current output from the DC/DC converter 11 is constant. is lit, the light intensity of each LED is 1/2, and when three LEDs are lit, the light intensity of each LED is 1/3.

A target value of the output current of the DC/DC converter 11 is set to a value equal to or less than the maximum allowable current of each of the red LED 20R, the green LED 20G, and the blue LED 20B. The closer the target output current is to the maximum allowable current, the higher the efficiency. It should be noted that the target value of the output current also needs to be less than or equal to the allowable current of the board and other parts in the lighting device 1 . In addition, the target value of the output current needs to satisfy the heat resistance condition for the substrates and parts in the lighting device 1 against heat dissipation by the output current.

In the circuit configuration according to the comparative example, when the red switch S1r, the green switch S1g, and the blue switch S1b are all turned off, the output voltage of the DC/DC converter 11 is equal to the input voltage (24 V in the example shown in FIG. ) is a problem. Since the DC/DC converter 11 is always controlled to output a constant current, the output voltage rises as the current flowing through the load approaches zero.

When any one of the red switch S1r, green switch S1g, and blue switch S1b is turned off, a high voltage equivalent to 24 V is momentarily applied to the LED connected to the switch. will be If the withstand voltage of the LED is exceeded due to this high voltage, the LED may malfunction.

FIG. 2 is a diagram showing a circuit configuration of lighting device 1 according to the embodiment of the present invention. A circuit configuration portion added to the circuit configuration according to the comparative example shown in FIG. 1 will be described below. In the circuit configuration according to the embodiment shown in FIG. 2, a dummy load 15 and a dummy load switch S2 are further connected in series between the power supply line W1 and the low side line W2.

In the example shown in FIG. 2, the dummy load 15 is composed of a dummy diode 20D and a fourth resistor R4 connected in series. The dummy diode 20D is a non-light emitting diode. A forward voltage drop Vf of a general silicon diode is about 0.6 to 0.7V. Therefore, the dummy diode 20D is configured by connecting a plurality of (for example, two) diode elements in series so as to approximate the forward voltage drop Vf of the LEDs connected in parallel.

A fourth resistor R4 connected to the anode terminal of the dummy diode 20D is a balance resistor for equalizing currents flowing through the red LED 20R, the green LED 20G, the blue LED 20B, and the dummy diode 20D. In order to equalize the loads of the four columns, the resistance value of the fourth resistor R4 and/or the number of resistive elements forming the fourth resistor R4 are adjusted.

Note that the row of dummy diodes 20D does not necessarily have to be designed to have the same load as the other three rows. The load on the row of dummy diodes 20D may be designed to be smaller than the loads on the other three rows within a range in which an increase in the output voltage of DC/DC converter 11 is permissible.

In the example shown in FIG. 2, an N-channel MOSFET is used for the dummy load switch S2, like the red switch S1r, the green switch S1g, and the blue switch S1b. The source terminal of the dummy load switch S2 is connected to the low side line W2, and the drain terminal is connected to the cathode terminal of the dummy diode 20D. An on/off signal is input from the second control circuit 13 to the gate terminal of the dummy load switch S2.

The second control circuit 13 monitors three drive signals (PWM signals) output from the first control circuit 12 for turning on/off the red switch S1r, the green switch S1g, and the blue switch S1b. do. The second control circuit 13 outputs a low level (off signal) to the gate terminal of the dummy load switch S2 when at least one of the three drive signals is high level (on signal). On the other hand, the second control circuit 13 outputs a high level (on signal) to the gate terminal of the dummy load switch S2 when all of the three drive signals are at low level (off signal).

The second control circuit 13 receives, for example, three drive signals for on/off-controlling the red switch S1r, the green switch S1g, and the blue switch S1b, and controls the dummy load switch S2 on/off. It can be configured by a NOR circuit that outputs a drive signal.

FIG. 3 summarizes the on/off relationship of the red switch S1r, the green switch S1g, and the blue switch S1b controlled by the first control circuit 12, and the dummy load switch S2 controlled by the second control circuit 13. It is a diagram.

As described above, according to the present embodiment, without PWM dimming in the DC/DC converter 11, PWM dimming is performed by the red switch S1r, the green switch S1g, and the blue switch S1b, and the DC/DC converter 11 continues to output a constant current. As a result, frequent repetition of stop and restart of the DC/DC converter 11 is eliminated, and the output noise of the DC/DC converter 11 is reduced. Audible noise is suppressed and quietness is improved.

Further, according to this embodiment, the three primary color LEDs are driven by one DC/DC converter 11 instead of three DC/DC converters. Thereby, the space in which the DC/DC converter 11 is installed can be saved. Therefore, the illumination device 1 can be miniaturized. Also, cost can be reduced by reducing the number of DC/DC converters.

Further, according to the present embodiment, the current output from one DC/DC converter 11 is divided by the LEDs in the ON path. By dividing the current, the power consumption is the same regardless of whether the number of LEDs to be lit is one, two, or three. When one LED lights up, a current can flow through the one LED up to the allowable power limit of the circuit board, and the ability of the LED can be fully exploited.

On the other hand, when three DC/DC converters are used to drive three primary color LEDs, basically only 1/3 of the allowable power of the circuit board can flow. If each of the three DC/DC converters grasps the lighting state of the LEDs of the three primary colors, more than 1/3 of the current can flow, but the circuit configuration becomes complicated. In contrast, according to the present embodiment, it is possible to sufficiently bring out the capabilities of the LED with a simple circuit configuration.

Depending on the performance of the three primary color LEDs, there may be times when all the three primary color LEDs are turned off. When the load of the DC/DC converter 11 becomes lighter, the output voltage rises and large noise occurs. In contrast, according to the present embodiment, the dummy load 15 is added, and the dummy load 15 is made conductive at the timing when all the LEDs of the three primary colors are turned off. As a result, the load applied to the DC/DC converter 11 becomes substantially constant regardless of the performance, the operation of the DC/DC converter 11 is stabilized, and noise is reduced. It should be noted that in a general presentation, the period in which all the LEDs of the three primary colors are turned off is extremely short, and the amount of current that is wastefully consumed is negligible.

On the other hand, if the DC/DC converter 11 is stopped every time all the LEDs of the three primary colors are turned off, large noise is generated. In addition, a signal line for notifying the DC/DC converter 11 that all three primary color LEDs are turned off is required, which complicates the circuit configuration.

The present invention has been described above based on the embodiments. It should be understood by those skilled in the art that the present embodiment is an example, and that various modifications can be made to the combination of each component, and that such modifications are within the scope of the present invention.

In the above embodiment, an example using LEDs of three primary colors has been described, but the present invention can be applied to any configuration in which a plurality of LEDs are connected in parallel. For example, a configuration in which a white LED and/or a yellow LED are further connected in parallel to a red LED, a green LED, and a blue LED is also applicable. It is also applicable to a configuration in which two color LEDs are connected in parallel, such as a red LED and a green LED, or a white LED and an orange LED. It is also applicable to a configuration in which a plurality of LEDs of the same color are connected in parallel. Even with a plurality of LEDs of the same color, if the installation positions are separated, it is possible to produce an effect with a plurality of LEDs.

Further, in the above-described embodiment, an example in which the first control circuit 12 and the second control circuit 13 are configured by separate IC chips has been described. In this regard, the first control circuit 12 and the second control circuit 13 may be integrated into one IC chip.

Also, in the above-described embodiments, an example in which a DC voltage is supplied from the outside has been described. In this respect, when an AC voltage is supplied from the outside, an AC/DC converter may be installed in front of the DC/DC converter 11 in the lighting device 1 .

Further, in the above-described embodiment, an example of using N-channel MOSFETs for the red switch S1r, the green switch S1g, the blue switch S1b, and the dummy load switch S2 has been described. In this regard, other types of switches such as bipolar transistors or relays may be used.

1 Lighting Device 11 DC/DC Converter 12 First Control Circuit 13 Second Control Circuit 15 Dummy Load 20R Red LED 20G Green LED 20B Blue LED 20D Dummy Diode S1r Red Switch S1g Green Switch S1b Blue switch S2 Dummy load switch F1 Fuse D1, D2 Diode L1 Inductor C1 Capacitor R1-R5 Resistor W1 Power supply line W2 Low side line.

Claims (4)

a plurality of LEDs (Light Emitting Diodes) connected in parallel;
a plurality of first switches connected in series to the plurality of LEDs;
a first control circuit that individually controls the plurality of first switches based on an input dimming signal;
a dummy load connected in parallel with the plurality of LEDs;
a second switch connected in series with the dummy load;
A power supply in which the plurality of LEDs and the dummy load are connected in parallel , regardless of the on/off state of each of the plurality of first switches, by converting an input DC voltage into constant-current DC power. a DC/DC converter that continues to output to the line;
monitoring a plurality of signals for controlling on/off of the plurality of first switches, and outputting a signal for controlling the second switch to be off when at least one of the plurality of signals includes an on signal; a second control circuit for outputting a signal for turning on the second switch when all of the plurality of signals are off signals;
A lighting device comprising: the plurality of LEDs connected in parallel are a red LED, a green LED and a blue LED;
there are three first switches;
2. The second control circuit according to claim 1, wherein the second control circuit outputs a signal for turning on the second switch when all of the three signals supplied to the three first switches are off signals. lighting system. 3. The lighting device according to claim 1, further comprising a plurality of balancing resistance elements connected in series to the plurality of LEDs, respectively, for equalizing currents flowing through the LEDs. The dummy load is
a non-light-emitting diode;
a balancing resistance element connected in series with the diode;
4. The lighting device according to any one of claims 1 to 3, comprising:

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