JP5734764B2 - LED lighting device, display device including the same, and control method of LED lighting device - Google Patents

Description

  The present invention relates to an LED lighting device, a display device including the same, and a method for controlling the LED lighting device.

  Conventionally, as shown in FIG. 5, an AC voltage supplied from an AC power source is full-wave rectified by a rectifying element (bridge diode) B1, and the rectified voltage is composed of a plurality of LEDs (LED1 to LEDn) connected in series. An LED lighting device for lighting the LED element 11 by adding to the LED element 11 is known.

  At this time, the current control unit 120 controls the current flowing through the LED element 11 to a constant current. Specifically, the current control unit 120 includes an N-type MOS transistor Q11, resistors R11 to R14, and a shunt regulator IC11. The transistor Q11 has a drain connected to the cathode of the LED element 11 and a source connected to the resistor R11. Resistors R12 and R13 output a reference voltage obtained by dividing the source voltage of the transistor Q11. The shunt regulator IC11 controls the gate voltage of the transistor Q11 so that the input reference voltage is constant. Thereby, since the voltage of the source of the transistor Q11 is controlled to be constant, the current flowing through the resistor R11 (that is, the current flowing through the LED element 11) is controlled to a constant current.

  As a device similar to this LED lighting device, for example, a device described in Patent Document 1 is known.

JP 2004-093657 A

  In the conventional LED lighting device described above, the LED element 11 is turned on when a constant current flows, so that the temperatures of the rectifying element B1, the LED element 11, and the current control unit 120 rise. In addition to the temperature increase due to this current, when the LED lighting device is installed outdoors, the temperature is likely to increase further due to the influence of direct sunlight, and the durability of the LED lighting device may be reduced due to the temperature increase. Further, when the forward voltage Vf of the LED element 11 decreases due to the temperature rise, the voltage applied to the transistor Q11 and the resistor R11 of the current control unit 120 increases, so that the power loss in the transistor Q11 and the resistor R11 increases. . For these reasons, it is preferable to suppress the temperature rise of the LED lighting device.

  Then, an object of this invention is to provide the LED lighting device which can suppress a temperature rise, a display apparatus provided with the same, and the control method of an LED lighting device.

An LED lighting device according to an embodiment according to one aspect of the present invention,
A rectifying element that rectifies an AC voltage supplied from an AC power source and outputs a rectified voltage between the first terminal and the second terminal;
An LED element having one end connected to the first terminal;
A current control unit that is connected between the other end of the LED element and the second terminal and controls the current flowing through the LED element to decrease as the temperature rises;

In the LED lighting device,
The current controller is
A current control element having one end connected to the other end of the LED element;
A first resistor connected between the other end of the current control element and the second terminal;
A step-down unit that steps down the voltage at the other end of the current control element by a temperature-dependent voltage that decreases as the temperature rises, and generates a reference voltage;
A voltage control unit that controls a voltage of a control terminal of the current control element so that the reference voltage is constant.

In the LED lighting device,
The step-down unit is
A diode element having an anode connected to the other end of the current control element;
You may have the 2nd resistance connected between the cathode of the said diode element, and the said 2nd terminal.

In the LED lighting device,
The temperature dependent voltage may decrease as the temperature of the diode element increases.

In the LED lighting device,
The diode element may include a plurality of diodes connected in series between the other end of the current control element and the second resistor.

In the LED lighting device,
The voltage controller is
A third resistor having one end connected to the first terminal;
A cathode is connected to the other end of the third resistor and a control terminal of the current control element, an anode is connected to the second terminal, the reference voltage is supplied to a reference terminal, and when the reference voltage increases, And a shunt regulator that increases the voltage of the cathode when the reference voltage decreases.

In the LED lighting device,
The rectifying element may be a bridge diode.

In the LED lighting device,
The LED element may include a plurality of LEDs connected in series between the first terminal and the current control unit.

In the LED lighting device,
The current control element may be an N-type MOS transistor.

In the LED lighting device,
Instead of the AC voltage from the AC power source, a DC voltage from a DC power source may be directly supplied between the first terminal and the second terminal without passing through the rectifying element.

A display device according to an embodiment of one aspect of the present invention includes:
The LED lighting device;
And a control unit for controlling whether or not to apply an AC voltage supplied from an AC power source to the rectifying element of the LED lighting device.

An LED lighting device control method according to an embodiment of one aspect of the present invention includes:
A rectifying element that rectifies an AC voltage supplied from an AC power source and outputs a rectified voltage between the first terminal and the second terminal, an LED element having one end connected to the first terminal, and the other end of the LED element And a current control unit connected between the second terminal, and a control method of an LED lighting device comprising:
The current control unit controls the current flowing through the LED element so as to decrease as the temperature rises.

  According to the LED lighting device according to one aspect of the present invention, the current control unit controls the current flowing through the LED element to decrease as the temperature rises. Thereby, when temperature rises, the electric current which flows into each part of a LED lighting device reduces. Therefore, temperature rise can be suppressed as compared with the case where a constant current is applied regardless of the temperature. Therefore, the durability of the LED lighting device can be increased, and power loss in the current control element or the like can be reduced.

1 is a circuit diagram of a display device including an LED lighting device according to Embodiment 1 of the present invention. FIG. 2 is a waveform diagram showing an input current of the LED lighting device according to Embodiment 1 of the present invention. FIG. 3 is a waveform diagram showing an input current of the LED lighting device according to Embodiment 1 of the present invention. FIG. 4 is a diagram illustrating a change over time in input current between the LED lighting device according to Embodiment 1 of the present invention and the conventional LED lighting device. FIG. 5 is a circuit diagram of a conventional LED lighting device.

  Embodiments according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a circuit diagram of a display device including an LED lighting device 10 according to Embodiment 1 of the present invention. The display device includes an LED lighting device 10 and a control unit (control panel) 20. The control unit 20 controls whether or not to apply the AC voltage supplied from the AC power source E to the LED lighting device 10 using, for example, a semiconductor relay SSR (Solid State Relay). In this embodiment, it is assumed that the display device constitutes a pedestrian traffic light.

  The LED lighting device 10 includes a rectifying element B1, an LED element 11, and a current control unit 12.

  The rectifying element B1 is a bridge diode composed of four diodes, and full-wave rectifies the AC voltage supplied from the AC power source E of the control unit 20 to rectify the voltage Vr between the first terminal T1 and the second terminal T2. Is output.

  The LED element 11 has an anode (one end) connected to the first terminal T1 of the rectifying element B1. In the present embodiment, the LED element 11 is composed of first to n-th plurality of LEDs (LED1 to LEDn) connected in series between the first terminal T1 and the current control unit 12.

  The current control unit 12 is connected between the cathode (the other end) of the LED element 11, that is, the cathode of the nth LED (LEDn), and the second terminal T <b> 2. It controls so that it decreases with.

  Specifically, the current control unit 12 includes an N-type MOS transistor (current control element) Q1, a first resistor R1, a step-down unit 13, and a voltage control unit 14.

  The N-type MOS transistor Q1 has a drain (one end) connected to the cathode of the LED element 11.

  The first resistor R1 is connected between the source (the other end) of the N-type MOS transistor Q1 and the second terminal T2.

  The step-down unit 13 steps down the source voltage Vs of the N-type MOS transistor Q1 by a temperature-dependent voltage that decreases as the temperature rises to generate a reference voltage Vref.

  The voltage control unit 14 controls the voltage Vg of the gate (control terminal) of the N-type MOS transistor Q1 so that the reference voltage Vref is constant.

  The step-down unit 13 includes a diode element D1 and a second resistor R2. The diode element D1 has an anode connected to the source of the N-type MOS transistor Q1. The second resistor R2 is connected between the cathode of the diode element D1 and the second terminal T2.

  In the present embodiment, it is assumed that the diode element D1 is composed of four diodes connected in series between the source of the N-type MOS transistor Q1 and the second resistor R2. These four diodes are connected so that a forward current flows from the source of the N-type MOS transistor Q1 to the second resistor R2.

  The temperature dependent voltage is the sum of the forward voltages Vf of the diodes constituting the diode element D1. Therefore, the temperature dependent voltage decreases as the temperature of the diode element D1 increases. Assuming that the temperature coefficient of the forward voltage Vf of one diode is about −2 mV / ° C., in this embodiment, the temperature coefficient of the temperature dependent voltage is about −8 mV / ° C.

  The voltage control unit 14 includes a third resistor R3 and a shunt regulator IC1. One end of the third resistor R3 is connected to the first terminal T1.

  In the shunt regulator IC1, the cathode is connected to the other end of the third resistor R3 and the gate of the N-type MOS transistor Q1, the anode is connected to the second terminal T2, and the reference voltage Vref is supplied to the reference terminal. The shunt regulator IC1 operates so that when the reference voltage Vref increases, the cathode voltage Vg decreases, and when the reference voltage Vref decreases, the cathode voltage Vg increases.

  With the above configuration, the LED lighting device 10 operates as follows.

  The rectified voltage Vr changes periodically between about 0 V and about 140 V, for example, according to the AC voltage. Then, in each period when the rectified voltage Vr is equal to or higher than a predetermined voltage, the LED element 11 is turned on, a current flows, and it is lit.

  The current of the LED element 11 is controlled to be substantially constant by the current controller 12 because the temperature-dependent voltage is constant under the condition of constant temperature. That is, the source voltage Vs of the N-type MOS transistor Q1 is stepped down by the temperature-dependent voltage of the diode element D1, and the reference voltage Vref is obtained. When the source voltage Vs of the N-type MOS transistor Q1 increases, the reference voltage Vref increases. Then, the cathode voltage Vg of the shunt regulator IC1 is lowered and the source voltage Vs of the N-type MOS transistor Q1 is lowered so that the reference voltage Vref is kept substantially constant. Therefore, the voltage Vs at the source of the N-type MOS transistor Q1, that is, the voltage Vs at one end of the first resistor R1, is kept substantially constant, so that the current flowing through the LED element 11 is controlled to be substantially constant.

  Thus, when a current flows through the rectifying element B1, the LED element 11, the N-type MOS transistor Q1, the first resistor R1, and the like, these generate heat and the temperature rises.

  When the temperature of the diode element D1 rises due to the temperature rise of each element or the temperature rise due to heat from the outside, the temperature dependent voltage drops with a temperature coefficient of about −8 mV / ° C. as described above. Therefore, even if the source voltage Vs of the N-type MOS transistor Q1 does not change, the reference voltage Vref increases. Then, the cathode voltage Vg of the shunt regulator IC1 is lowered and the source voltage Vs of the N-type MOS transistor Q1 is lowered so that the reference voltage Vref is kept substantially constant. Therefore, the current flowing through the LED element 11 decreases.

  Contrary to this operation, when the temperature decreases, the current flowing through the LED element 11 increases.

  FIG. 2 is a waveform diagram showing an input current of the LED lighting device 10 according to the first embodiment of the present invention. FIG. 2 shows an initial state immediately after energization. The vertical axis of the figure shows the input current input from the AC power source E to the LED lighting device 10, and the horizontal axis shows time. As shown in the figure, the input current is a rectangular wave that changes positively and negatively, and its cycle is equal to the cycle of the AC voltage of the AC power source E. The maximum absolute value of the input current is controlled to a substantially constant value. Most of the input current is a current flowing through the LED element 11.

  FIG. 3 is a waveform diagram showing an input current of the LED lighting device 10 according to the first embodiment of the present invention. FIG. 3 shows a state after energization for 30 minutes from the initial state of FIG. The vertical and horizontal axes in the figure are the same scale as in FIG.

  As can be seen from the range A shown in FIGS. 2 and 3, the maximum value of the input current input from the AC power source E to the LED lighting device 10 decreases after 30 minutes of energization. This is due to the temperature rise.

  FIG. 4 is a diagram showing a time change of input current between the LED lighting device 10 according to the first embodiment of the present invention and the conventional LED lighting device (FIG. 5). The vertical axis in the figure indicates the average value of the input current input from the AC power source E to the LED lighting device 10, and the horizontal axis indicates time.

  As shown in the figure, in the LED lighting device 10 of the present embodiment, the average value of the input current decreases with the passage of time. That is, the average value of the input current is about 80 mA in the initial state, and is reduced to about 75.5 mA after energization for 30 minutes. In the period of 30 minutes, for example, the temperature of the N-type MOS transistor Q1 has increased by about 35 ° C. due to the influence of energization.

  On the other hand, in the conventional LED lighting device of FIG. 5, the average value of the input current does not decrease with the passage of time, and is controlled to a substantially constant current even after energization for 30 minutes. During the period of 30 minutes, for example, the temperature of the N-type MOS transistor Q11 of FIG.

  Thus, the LED lighting device 10 of the present embodiment can suppress the temperature rise as compared with the conventional LED lighting device.

  As described above, according to the LED lighting device 10 of the present embodiment, the step-down unit 13 steps down the source voltage Vs of the N-type MOS transistor Q1 by a temperature-dependent voltage that decreases as the temperature rises. The reference voltage Vref is generated, and the voltage controller 14 controls the voltage Vg of the gate of the N-type MOS transistor Q1 so that the reference voltage Vref becomes constant. Thereby, when the temperature rises, the reference voltage Vref increases. Then, the voltage control unit 14 decreases the voltage Vg of the gate of the N-type MOS transistor Q1 so that the reference voltage Vref becomes constant, so that the current of the N-type MOS transistor Q1 decreases. That is, when the temperature rises, the current flowing through each part of the LED lighting device 10 decreases.

  Therefore, the temperature rise caused by the current can be more effectively suppressed than when a constant current is applied regardless of the temperature. Thereby, durability of the LED lighting device 10 can be increased.

  In particular, in a pedestrian traffic light installed outdoors, the temperature of the LED lighting device 10 is more likely to rise due to the influence of direct sunlight. According to the LED lighting device 10 of the present embodiment, since the temperature rise can be suppressed as compared with the conventional LED lighting device, the durability of the LED lighting device 10 can be increased even under such conditions.

  In addition, when the temperature rise is suppressed, a decrease in the forward voltage Vf of the LED element 11 can be suppressed, so that an increase in voltage applied to the N-type MOS transistor Q1 and the resistor R1 can be suppressed. Accordingly, power loss in the N-type MOS transistor Q1 and the resistor R1 can be reduced.

  Further, if the resistor R12 in the conventional LED lighting device of FIG. 5 is replaced with the diode element D1, the LED lighting device 10 of the present embodiment can be realized, so that the temperature rise can be suppressed without using a complicated control circuit.

  Further, since the temperature coefficient of the temperature-dependent voltage can be changed by increasing or decreasing the number of diodes connected in series constituting the diode element D1, the current reduction rate with respect to the temperature rise can be easily changed.

  Furthermore, since the control part (control panel) 20 is the same as the control part of the existing pedestrian traffic light using the incandescent light bulb, the incandescent light bulb of the pedestrian traffic light using the incandescent light bulb is replaced with the LED of this embodiment. A pedestrian traffic light using LEDs can be easily realized at low cost simply by replacing the lighting device 10 with the lighting device 10.

  As mentioned above, although the Example of this invention was explained in full detail, a concrete structure is not limited to the said Example, A various deformation | transformation can be implemented in the range which does not deviate from the summary of this invention.

For example, instead of the AC voltage from the AC power source E, a DC voltage from the DC power source may be directly supplied between the first terminal T1 and the second terminal T2 without passing through the rectifying element B1.
Moreover, although the example which the display apparatus comprises the pedestrian traffic light was demonstrated, it is not restricted to this. The display device may constitute an automobile traffic light or may be a device that displays some information by turning on and off the LED element 11.

  Moreover, the diode element D1 may be comprised by one diode, and may be comprised by the some diode connected in series. Furthermore, the LED element 11 may be comprised by one LED.

DESCRIPTION OF SYMBOLS 10 LED lighting apparatus B1 Rectifier element 11 LED element 12 Current control part 13 Buck part 14 Voltage control part LED1-LEDn LED
Q1 N-type MOS transistor (current control element)
R1 1st resistance R2 2nd resistance R3 3rd resistance D1 Diode element IC1 Shunt regulator 20 Control part

Claims (11)

A rectifying element that rectifies an AC voltage supplied from an AC power source and outputs a rectified voltage between the first terminal and the second terminal;
An LED element having one end connected to the first terminal;
A current control unit that is connected between the other end of the LED element and the second terminal and controls the current flowing through the LED element to decrease as the temperature rises ;
The current controller is
A current control element having one end connected to the other end of the LED element;
A first resistor connected between the other end of the current control element and the second terminal;
A step-down unit that steps down the voltage at the other end of the current control element by a temperature-dependent voltage that decreases as the temperature rises, and generates a reference voltage;
A voltage control unit that controls a voltage of a control terminal of the current control element so that the reference voltage is constant ; The step-down unit is
A diode element having an anode connected to the other end of the current control element;
LED lighting device according to claim 1, characterized in that it comprises a second resistor connected between the cathode and the second terminal of the diode element. The LED lighting device according to claim 2 , wherein the temperature-dependent voltage decreases as the temperature of the diode element increases. The diode element, LED lighting according to claim 2 or claim 3, characterized in that it is composed of a plurality of diodes connected in series between the other end and the second resistor of the current control element apparatus. The voltage controller is
A third resistor having one end connected to the first terminal;
A cathode is connected to the other end of the third resistor and a control terminal of the current control element, an anode is connected to the second terminal, the reference voltage is supplied to a reference terminal, and when the reference voltage increases, It decreases the voltage, LED lighting device according to any one of claims 1 to 4, characterized in that it comprises a shunt regulator voltage of the cathode and the reference voltage is reduced to increase. The LED lighting device according to any one of claims 1 to 5 , wherein the rectifying element is a bridge diode. The LED lighting according to any one of claims 1 to 6 , wherein the LED element includes a plurality of LEDs connected in series between the first terminal and the current control unit. apparatus. It said current control element, LED lighting device according to any one of claims 1 to 5, characterized in that the N-type MOS transistor. The DC voltage from a DC power supply is directly supplied between the first terminal and the second terminal without passing through the rectifying element instead of the AC voltage from the AC power supply. The LED lighting device according to claim 8 . The LED lighting device according to any one of claims 1 to 8 ,
A control unit that controls whether or not to apply an AC voltage supplied from an AC power source to the rectifying element of the LED lighting device. A rectifying element that rectifies an AC voltage supplied from an AC power source and outputs a rectified voltage between the first terminal and the second terminal, an LED element having one end connected to the first terminal, and the other end of the LED element And a current control unit connected between the second terminal and the current control unit , wherein the current control unit includes a current control element having one end connected to the other end of the LED element, and the other end of the current control element. said first resistor connected between the second terminal, that Yusuke and step-down unit, a voltage control unit, a method of controlling an LED lighting device and,
By the step-down unit, the voltage at the other end of the current control element is stepped down by a temperature-dependent voltage that decreases as the temperature rises to generate a reference voltage,
The voltage control unit controls the voltage of the control terminal of the current control element so that the reference voltage is constant,
The method for controlling an LED lighting device, wherein the current control unit controls the current flowing through the LED element to decrease as the temperature rises.

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