JP2010021008A - Led lighting device - Google Patents

Abstract

An object of the present invention is to provide an LED illumination device capable of dimming irradiation light with a simple and inexpensive configuration.
A first series in which a first LED group having a first emission color and a first switch element are connected in series to an output terminal of a DC-DC converter having a constant current feedback loop. An LED lighting device 100 that connects a circuit 20 and a second series circuit 30 in which a second LED group 31 having a second emission color and a second switch element 32 are connected in series. A current detection element 40 that detects a combined current A0 of currents flowing through the column circuit 20 and the second series circuit 30; and a control circuit 50 that controls the first LED group 21 and the second LED group 31. The DC-DC converter 10 controls so that the value of the combined current A0 detected by the current detection element 40 becomes constant, and the control circuit 50 complementarily connects the first switch element 22 and the first switch element 22. Turn on and off Please is carried out.
[Selection] Figure 1

Description

  The present invention relates to an LED lighting device. More specifically, it relates to dimming of the LED lighting device.

  In recent years, with the development of high-intensity LEDs, there is an illuminating device that uses an LED that has been used mainly for display as a light source for illumination. The illuminating device using such an LED includes a conventional fluorescent lamp and an illuminating device having LEDs with different emission colors in order to reproduce the irradiation light color close to natural light or freely change the irradiation light color. is there.

  In such an illuminating device, a method for controlling a direct current flowing in an LED is known as means for changing the brightness of illumination light and the color of irradiated light.

  However, in order to change the brightness of the illumination light or the color of the irradiation light, it is necessary to provide a constant current circuit for each LED having a different emission color. In addition, there is a problem that the control becomes complicated in order to change only the illumination light color while keeping the brightness of the illumination light constant, or to change only the brightness of the illumination light while keeping the illumination light color constant. It was.

  Therefore, a device using a pulse width modulation signal is known as means for controlling the average current flowing in the LED. The brightness of the illumination light and the color of the irradiated light are changed by blinking the LEDs of the respective emission colors based on the pulse width modulation signal. The illumination light color can be changed by changing the brightness of the illumination light by changing the turn-off time of the LED of each emission color, and changing the ratio of the turn-on time of the LED of each emission color. For example, as described in Patent Document 1. By doing so, the brightness of the illumination light and the color of the irradiated light can be changed without providing a control circuit for changing the current value.

However, in the technique of Patent Document 1 described above, in order to obtain desired illumination light brightness and irradiation light color by the pulse width modulation signal, it is necessary to make the current value flowing through the LEDs of the respective emission colors constant. . Therefore, it is necessary to provide a DC-DC converter (constant current power supply circuit) having constant current feedback for each light emitting LED, which is disadvantageous in terms of increase in the number of parts and cost increase.
JP 2005-142137 A

  The present invention has been made in view of such problems, and it is possible to change the brightness of the irradiation light while keeping the color of the irradiation light constant with a simple and inexpensive configuration, or to keep the brightness of the irradiation light constant. It aims at provision of the LED illuminating device which can change an irradiation light color.

In claim 1, a first series circuit in which a first LED group having a first emission color and a first switch element are connected in series to an output terminal of a DC-DC converter having a constant current feedback loop; A second LED circuit having a second emission color and a second series circuit in which a second switch element is connected in series;
A control circuit that controls the first LED group and the second LED group; and a current detection element that detects a combined current of currents flowing through the first series circuit and the second series circuit. ,
The control circuit performs control to turn off the second switch element when the first switch element is on, and to turn on the second switch element when the first switch element is off. The DC converter performs control so that the value of the combined current detected by the current detection element is constant.

3. The DC-DC converter according to claim 2, wherein the DC-DC converter includes a constant voltage feedback loop, and an output voltage of the DC-DC converter in which the constant voltage feedback loop operates is the DC-DC in which the constant current feedback operates. Set higher than the output voltage of the converter,
The control circuit turns off the second switch element when the first switch element is on, and turns on the second switch element when the first switch element is off. The first switch element and the second switch element are controlled so as to provide a time for turning off at the same time for a very short time.

  As effects of the present invention, the following effects can be obtained.

  According to the first aspect of the present invention, the combined current of the currents flowing through the first series circuit and the second series circuit is controlled to a constant value by the DC-DC converter having the constant current feedback loop and the current detection element. . Here, since only one of the first LED group and the second LED group is lit by the control circuit, the value of the combined current detected by the current detection element is either one of the lit LEDs. It is the maximum current flowing in the group. Therefore, a single DC-DC converter with constant current feedback makes it possible to control the current flowing through multiple LED groups to a constant value, and by changing the maximum current value, the color of the emitted light can be kept constant with a simple and inexpensive configuration. It is possible to change the brightness of the irradiation light while maintaining the above.

  Since it comprised like Claim 2, even if the total on-duty ratio of a 1st LED group and a 2nd LED group is the operation state of about 100%, it is ensured that a 1st LED group and a 2nd LED group light simultaneously. Can be prevented. At this time, even if both the first switch element and the second switch element are turned off and no current flows, the output voltage is suppressed to a voltage at which constant voltage feedback operates. Therefore, the DC-DC converter may have a power capacity capable of lighting one LED group, and can change the brightness of the irradiation light while keeping the irradiation light color constant with a simple and inexpensive configuration.

  Next, an LED lighting device 100 that is an embodiment of the LED lighting device according to the present invention will be described with reference to FIGS. 1, 2, and 5. In addition, although the LED lighting apparatus 100 according to the present embodiment includes two LED groups, the present invention is not limited to this.

  As shown in FIG. 1, the LED lighting device 100 changes the brightness of illumination light and the color of irradiated light by combining LEDs having different emission colors. The LED lighting device 100 mainly includes a DC-DC converter 10, a first series circuit 20, a second series circuit 30, a current detection element 40, a control circuit 50, and the like.

  The DC-DC converter 10 converts the output current to a constant current. The DC-DC converter 10 mainly includes an input terminal 11, a voltage conversion circuit 12, a constant current feedback loop 13, an output terminal 14, a current detection element 40, and the like.

  The input terminal 11 is a terminal for inputting the input voltage V0 and is connected to the power supply 1.

  The voltage conversion circuit 12 transforms a direct current voltage, transforms the input voltage V0 input from the input terminal 11 to a predetermined voltage, and outputs it as an output voltage V1.

  The constant current feedback loop 13 feeds back the fluctuation of the output current. The constant current feedback loop 13 mainly includes an operational amplifier 13a and a reference voltage source 13b. The negative terminal of the operational amplifier 13a is connected to the high potential side terminal P1 of the current detection element 40, and the positive terminal of the operational amplifier 13a is connected to the reference voltage source 13b. The reference voltage source 13b determines a current value output from the DC-DC converter 10, and the voltage Va of the reference voltage source 13b is configured to be set to an arbitrary value. The constant current feedback loop 13 generates a voltage corresponding to the potential difference between the voltage applied to the current detection element 40 input to the negative terminal of the operational amplifier 13a and the voltage Va input to the positive terminal of the operational amplifier 13a. Enter.

  The output terminal 14 outputs a voltage. In the present embodiment, the first series circuit 20 and the second series circuit 30 are connected in parallel to the output terminal 14.

  The current detection element 40 detects a current value. In this embodiment, the current detection element 40 is configured by a resistor R1, and is connected between the voltage conversion circuit 12 and the first series circuit 20 and the second series circuit 30 that are configured in parallel. The value of the voltage V2 generated in the resistor R1 is detected by a current (hereinafter referred to as a combined current) A0 that flows when the current A1 that flows through the column circuit 20 and the current A2 that flows through the second series circuit 30 merge.

  The first series circuit 20 constitutes a light source of the LED lighting device 100. The first series circuit 20 is configured by connecting a first LED group 21 having a first emission color and a first switch element 22 in series. The first LED group 21 is turned on when the first switch element 22 is on, and is turned off when the first switch element 22 is off.

The second series circuit 30 constitutes a light source of the LED lighting device 100. The second series circuit 30 is configured by connecting a second LED group 31 having a second emission color and a second switch element 32 in series. The second LED group 31 is turned on when the second switch element 32 is on, and is turned off when the second switch element 32 is off.
The first LED group 21 having the first emission color and the second LED group 31 having the second emission color are lit as close as possible, and the total lighting cycle of the first LED group 21 and the second LED group 31 is fast. When (100 Hz or more is desirable), the irradiation light is recognized as an intermediate color according to the lighting time ratio of the first emission color and the second emission color.

  The control circuit 50 performs on / off control of the first switch element 22 and the second switch element 32. In the control circuit 50, the first switch element 22 and the second switch element 32 are connected. The control circuit 50 inputs the pulse width modulation signal S1 to the control input terminal (gate) of the first switch element 22 to turn on and off the first switch element 22, and the pulse width modulation signal S2 obtained by inverting the pulse width modulation signal S1. Is input to the control input terminal (gate) of the second switch element 32 to turn the second switch element 32 on and off. That is, the control circuit 50 performs control to turn off the second switch element 32 when the first switch element 22 is on, and turn on the second switch element 32 when the first switch element 22 is off.

  Below, the control aspect of the LED lighting apparatus 100 is demonstrated.

  The DC-DC converter 10 outputs the input voltage V0 from the power source 1 input to the input terminal 11 from the output terminal 14 as the output voltage V1 by the voltage conversion circuit 12.

The voltage Va is input to the + terminal of the operational amplifier 13a. The voltage V2 applied to the current detection element 40 is input to the negative terminal of the operational amplifier 13a. The operational amplifier 13a compares the voltage V2 with the voltage Va. If the voltage Va is larger than the voltage V2, the voltage according to the potential difference is input to the voltage conversion circuit 12, and the voltage conversion circuit 12 increases the output voltage V1. Further, when the voltage Va and the voltage V2 are equal, or when the voltage Va is smaller than the voltage V2, the voltage conversion circuit 12 decreases the output voltage.
Therefore, the DC-DC converter 10 can control the voltage conversion circuit 12 so that the voltage V2 and the voltage Va coincide with each other by the constant current feedback loop 13, thereby making the output current constant.

  As shown in FIG. 2A, the first LED group 21 blinks by the first switch element 22 that is turned on / off based on the pulse width modulation signal S1 from the control circuit 50, and the second LED group 31 is controlled. The blinking operation is performed by the second switch element 32 which is turned on / off based on the pulse width modulation signal S2 from the circuit 50. Therefore, since only one of the first LED group 21 and the second LED group 31 is lit, the current from the DC-DC converter 10 flows only to the lit LED group. That is, the value of the combined current A0 detected by the current detection element 40 is equal to the current A1 flowing through the first LED group 21 or the current A2 flowing through the second LED group 31.

  When changing the brightness of the irradiated light, as shown in FIGS. 2A and 2B, the current A1 and the second current flowing in the first LED group 21 are changed by changing the voltage Va of the reference voltage source 13b. The current A2 flowing through the LED group 31 is changed. The DC-DC converter 10 controls the constant voltage feedback loop 13 so that the voltage V2 becomes the changed voltage Va. Thereby, the brightness of the irradiation light of the first LED group 21 and the second LED group 31 is changed. At this time, since the value of the combined current A0 detected by the current detection element 40 is equal to the current A1 flowing through the first LED group 21 and the current A2 flowing through the second LED group 31, the irradiation light of the first LED group 21 The brightness and the brightness of the irradiation light of the second LED group 31 are simultaneously changed equally. That is, the current A1 flowing through the first LED group 21 and the current A2 flowing through the second LED group 31 can be controlled to a constant value with one DC-DC converter 10 having the constant current feedback loop 13.

  When changing the irradiation light color of the irradiation light, as shown in FIGS. 5A and 5B, the pulse width modulation signal S1 and the pulse width modulation signal S2 are changed, and the average current value flowing through each LED group is changed. To change. While maintaining the total lighting time Ton of the first LED group 21 and the second LED group 31, the ratio of the lighting time T1on of the first LED group 21 and the lighting time T2on of the second LED group 31 is changed. By doing so, the ratio of each emission color changes, but the total lighting time Ton does not change, so the total brightness of the irradiation light of the first LED group 21 and the irradiation light of the second LED group 31 changes. Without changing, only the color of the irradiated light can be changed.

As described above, the first LED group 21 having the first emission color and the first switch element 22 are connected in series to the output terminal 14 of the DC-DC converter 10 having the constant current feedback loop 13. An LED lighting device 100 that connects in parallel a column circuit 20, a second series circuit 30 in which a second LED group 31 having a second emission color and a second switch element 32 are connected in series,
A control circuit 50 that controls the first LED group 21 and the second LED group 31; a current detection element 40 that detects a combined current A0 of currents flowing through the first series circuit 20 and the second series circuit 30; Comprising
The control circuit 50 controls to turn off the second switch element 32 when the first switch element 22 is on, and to turn on the second switch element 32 when the first switch element 22 is off. The converter 10 performs control so that the value of the combined current A0 detected by the current detection element 40 is constant.
With this configuration, the current A1 flowing in the first series circuit 20 and the current A2 flowing in the second series circuit 30 by the DC-DC converter 10 including the constant current feedback loop 13 and the current detection element 40 The combined current A0 is controlled to a constant value. Here, since only one of the first LED group 21 and the second LED group 31 is turned on by the control circuit 50, the combined current A0 detected by the current detection element 40 is turned on. This is the maximum current flowing in the LED group. Therefore, a single DC-DC converter 10 having a constant current feedback loop 13 can control the current flowing in a plurality of LED groups to a constant value, and by changing the maximum current value, the constant current can be maintained with a simple and inexpensive configuration. The brightness of the irradiation light can be changed while maintaining the irradiation light color.

  Below, 2nd embodiment of the LED lighting apparatus which concerns on this invention is described using FIG.3, FIG.4 and FIG.5. Note that, in the following embodiments, the same points as those of the first embodiment described above are denoted by the same reference numerals, the detailed description thereof will be omitted, and differences will be mainly described.

  As shown in FIG. 3, the LED lighting device 200 of the second embodiment includes a DC-DC converter 10 including a constant current feedback loop 13 and a constant voltage feedback loop 15.

The reference voltage source 13b is connected to the + terminal of the operational amplifier 13a provided in the constant current feedback loop 13, and the-terminal of the operational amplifier 13a is connected to the low potential side of the current detection element 40 through the resistor R2 and is connected to the resistor. It is connected to the reference voltage source 15b via R3. At this time, the terminal P1 on the high potential side of the current detection element 40 (the negative side of the reference voltage sources 13b and 15b) is set to GND (reference potential), and the voltage of the terminal P2 on the low potential side of the current detection element 40 is set to −V2. For example, the voltage input to the negative terminal of the operational amplifier 13a is the voltage V3 obtained by subtracting the voltage V2 from the voltage obtained by dividing the reference voltage source Vb and the voltage V2 by the resistors R3 and R2. Is done. Therefore, when the output current increases, the voltage applied to the resistor R1 increases and the voltage V3 input to the negative terminal of the operational amplifier 13a decreases.
The constant current feedback loop 13 converts a voltage according to a potential difference between the voltage Va of the reference voltage source 13b input to the + terminal of the operational amplifier 13a and the voltage V3 applied to the resistor R2 input to the − terminal of the operational amplifier 13a to a voltage conversion circuit. 12 is input.

The constant voltage feedback loop 15 feeds back the output voltage V1. The constant voltage feedback loop 15 mainly includes an operational amplifier 15a and a reference voltage source 15b. The resistor R4 and the resistor R5 are connected to both ends of the first series circuit 20 and the second series circuit 30 that are configured in parallel. The positive terminal of the operational amplifier 15a is connected between the resistors R4 and R5, and the negative terminal of the operational amplifier 15a is connected to the reference voltage source 15b.
In the constant voltage feedback loop 15, the voltage V4 obtained by dividing the output voltage V1 by the resistors R4 and R5 is input to the + terminal of the operational amplifier 15a, and this voltage V4 and the reference voltage input to the-terminal of the operational amplifier 15a. A voltage corresponding to the potential difference between the voltage Vb of the source 15b and the voltage conversion circuit 12 is input. Further, the output voltage V1 of the DC-DC converter 10 in which the constant voltage feedback loop 15 operates is the output voltage V1 when the constant current feedback loop 13 is operated by the voltage Vb of the resistor R4, the resistor R5 and the reference voltage source 15b. Higher voltage V1max.

  The constant current feedback loop 13 and the constant voltage feedback loop 15 input a voltage to the voltage conversion circuit 12 via the OR circuit 16 and the transistor 17. The OR circuit 16 inputs a voltage to the voltage conversion circuit 12 when at least one of the constant current feedback loop 13 and the constant voltage feedback loop 15 inputs a voltage to the OR circuit 16.

The control circuit 50 performs on / off control of the first switch element 22 and the second switch element 32. The control circuit 50 is connected to the first switch element 22 and the second switch element 32. The control circuit 50 inputs the pulse width modulation signal S1 to the first switch element 22, turns on the first switch element 22, and inputs the pulse width modulation signal S2 obtained by inverting the pulse width modulation signal S1 to the second switch element 32. Then, the second switch element 32 is turned on / off.
At this time, the first switch element 22 and the second switch element 32 are controlled so as to provide a very short time for turning off at the same time. That is, when the first switch element 22 is turned off, the control circuit 50 turns on the second switch element 32 after the lapse of time T1, and when the second switch element 32 is turned off, the control circuit 50 turns off the first switch element 22 after the lapse of time T2. Control to turn on. Time T1 and time T2 may be equal.

  Below, the control aspect of the LED lighting apparatus 200 is demonstrated.

The voltage Va of the reference voltage source 13b is input to the + terminal of the operational amplifier 13a. The voltage V3 obtained by subtracting the voltage V2 from the voltage obtained by dividing the voltage obtained by adding the reference voltage source Vb and the voltage V2 by the resistor R3 and the resistor R2 is input to the negative terminal of the operational amplifier 13a. Therefore, when the output current increases, the voltage applied to the resistor R1 increases, and the voltage V3 input to the negative terminal of the operational amplifier 13a decreases. The operational amplifier 13a compares the voltage Va of the reference voltage source 13b with the voltage V3, and if the voltage Va is larger than the voltage V3, the voltage is supplied to the voltage conversion circuit 12 by biasing the transistor 17 with a voltage corresponding to the potential difference. input. Therefore, the voltage conversion circuit 12 decreases the output voltage V1. The operational amplifier 13a turns off the transistor 17 by inputting 0V to the transistor 17 when the voltage Va is lower than the voltage V3 or when the voltage Va is equal to the voltage V3. Therefore, the voltage conversion circuit 12 increases the output voltage. While the constant current feedback loop 13 is working, the voltage Rb of the resistor R4, the resistor R5, and the reference voltage source 15b is set so that the constant voltage feedback loop 15 does not work.
Therefore, the DC-DC converter 10 can make the output current value constant by controlling the voltage conversion circuit 12 so that the voltage V3 and the voltage Va are matched by the constant current feedback loop 13.

  The first LED group 21 blinks by the first switch element 22 that is turned on / off based on the pulse width modulation signal S 1 from the control circuit 50, and the second LED group 31 receives the pulse width modulation signal S 2 from the control circuit 50. Based on this, the second switch element 32 that turns on and off blinks. At this time, since the first LED group 21 and the second LED group 31 are provided with a time T1 and a time T2 that are turned off at the same time, it is ensured that both LED groups are turned on at the same time due to variations in operation time of the switch elements. Can be prevented. That is, since only one of the first LED group 21 and the second LED group 31 is lit, the DC-DC converter 10 may have a power capacity capable of lighting one LED group. (See FIG. 4).

  Here, no current flows through the current detection element 40 during the time T1 and the time T2 when the first LED group 21 and the second LED group 31 are turned off simultaneously. At this time, the voltage V3 at the minus terminal of the operational amplifier 13a becomes the same potential as the voltage Va, and the operational amplifier 13a inputs 0V to the transistor 17 to turn off the transistor 17. Therefore, the voltage conversion circuit 12 increases the output voltage V1. The voltage conversion circuit 12 raises the output voltage V1 to a voltage V1max at which the voltage V4 obtained by dividing the output voltage V1 by the resistors R4 and R5 is equal to the voltage Vb, thereby making the voltage constant (see FIG. 4).

  When changing the brightness of the irradiation light, the voltage Va of the reference voltage source 13b is changed, and as shown in FIGS. 5A and 5C, the lighting time T1on and the second LED of the first LED group 21 are changed. It is also possible to change the lighting time T1on and the lighting time T2on by changing the lighting time T1on and the lighting time T2on of the group 31 at a constant ratio. By controlling in this way, the light emission ratio between the first LED group 21 and the second LED group 31 does not change, and the time during which both the first LED group 21 and the second LED group 31 are turned off increases. Therefore, the brightness of the irradiation light can be changed without changing the irradiation light color.

  When changing the irradiation light color, as shown in FIG. 5A and FIG. 5B, the ratio of the on-duty between the first LED group 21 and the second LED group 31 is changed as described above. Is possible.

As described above, the DC-DC converter 10 includes the constant voltage feedback loop 15, and the output voltage V1max of the DC-DC converter 10 that operates the constant voltage feedback loop 15 is DC− that operates the constant current feedback loop 13. Set higher than the output voltage Va of the DC converter 10,
The control circuit 50 turns off the second switch element 32 when the first switch element 22 is on, and turns on the second switch element 32 when the first switch element 22 is off. Control is performed so as to provide time T1 and time T2 at which the one switch element 22 and the second switch element 32 are simultaneously turned off.
With this configuration, the first LED group 21 and the second LED group 31 are simultaneously lit even in an operation state where the total on-duty ratio of the first LED group 21 and the second LED group 31 is approximately 100%. This can be surely prevented. At this time, even if the first switch element 22 and the second switch element 32 are both turned off and no current flows, the output voltage V1 is suppressed to the voltage V1max at which the constant voltage feedback loop 13 operates. Therefore, the DC-DC converter may have a power capacity capable of lighting one LED group, and can change the brightness of the irradiation light while keeping the irradiation light color constant with a simple and inexpensive configuration.

BRIEF DESCRIPTION OF THE DRAWINGS The whole block diagram of the LED illuminating device which concerns on 1st embodiment of this invention. (A) The figure showing the operation state of each LED which concerns on 1st embodiment of this invention. (B) The figure showing the operation state of each LED which concerns on 1st embodiment of this invention. The whole block diagram of the LED lighting device according to the second embodiment of the present invention. The figure showing the operation state of each LED which concerns on 2nd embodiment of this invention. (A) The figure showing the operation state of each LED which concerns on this invention. (B) The figure showing the operation state of each LED concerning the present invention. (C) The figure showing the operation state of each LED concerning the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 DC-DC converter 14 Output terminal 20 1st series circuit 21 1st LED group 22 1st switch element 30 2nd series circuit 31 2nd LED group 32 2nd switch element 40 Current detection element 50 Control circuit 100 LED lighting apparatus

Claims (2)

To the output terminal of the DC-DC converter with a constant current feedback loop,
A first series circuit in which a first LED group having a first emission color and a first switch element are connected in series;
A second series circuit in which a second LED group having a second emission color and a second switch element are connected in series;
LED lighting devices connected in parallel,
A control circuit for controlling the first LED group and the second LED group;
A current detection element for detecting a combined current of currents flowing through the first series circuit and the second series circuit;
Comprising
The control circuit controls to turn off the second switch element when the first switch element is on, and to turn on the second switch element when the first switch element is off,
The LED lighting device according to claim 1, wherein the DC-DC converter controls the value of the combined current detected by the current detection element to be constant. The DC-DC converter
An output voltage of the DC-DC converter that includes a constant voltage feedback loop and that operates the constant voltage feedback loop is set higher than an output voltage of the DC-DC converter that operates the constant current feedback,
The control circuit includes:
When the first switch element is on, the second switch element is turned off, and when the first switch element is off, the second switch element is turned on. The LED lighting device according to claim 1, wherein control is performed so as to provide a time for turning off the second switch element at the same time.

Images