JP2003188415A - Led lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an LED lighting device which has a small change in light quantity since power is turned on. <P>SOLUTION: The LED lighting device has LEDs 1, a control section (microcomputer) 2 capable of controlling currents applied to the LEDs 1, and a means for practically detecting temperatures of the LEDs 1. Based on the characteristics of 'ambient temperature (Ta) - luminous intensity (IV)' of the LEDs 1, the LEDs 1 are changed in currents to keep a substantially constant light quantity. Then, the temperatures of the LEDs are detected based on the measured values of forward currents (IF) and forward voltages (VF) of the LEDs 1. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED (light emitting diode) lighting device.

[0002]

2. Description of the Related Art One of the uses of an LED lighting device is to illuminate an object to be inspected such as various manufactured articles. Then, the object to be inspected illuminated by the LED is photographed by a CCD camera, and the image is processed to inspect the object to be inspected. A large amount of light is required to illuminate the inspection target, and a large number of LEDs are generally used.

[0003]

However, the LED
A large amount of heat is generated by using a large number of. First of all, LE
D has inherent characteristics such as a decrease in luminous intensity (IV) and a decrease in forward voltage (VF) due to heat, and an increase in forward current due to a decrease in forward voltage, and an increase in a forward voltage accordingly, causes the light amount to increase. It should be noted that there is a problem to be solved that it takes a considerable waiting time before the inspection starts because it takes time to stabilize. In view of such problems to be solved, the present invention is an LE in which the change in the light amount after power-on is small
It is an object to provide a D lighting device.

[0004]

SUMMARY OF THE INVENTION The present invention is an LED and an L
It has a control unit that can control the current flowing through the ED and a means that substantially detects the temperature of the LED, and the "ambient temperature (T
a) -luminance (IV) ", the LED lighting device changes the current of the LED to keep the light amount substantially constant. The temperature of the LED may be detected based on the measured values of the forward current and the forward voltage of the LED, or may be detected by a temperature sensor arranged near the LED.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the present invention will be described, but it is merely an exemplary embodiment adopted based on the present invention, and the present invention is based on matters peculiar to the embodiment. However, the technical scope of the present invention should be determined based on the matters shown in the claims and the matters substantially equivalent to the matters.

In the embodiment shown in FIGS. 1 to 6, the LEDs 1 ...
"Ambient temperature (Ta) -luminous intensity (IV)" of the LED 1 having a control unit (microcomputer) 2 capable of controlling the current flowing through the LEDs 1, and means for substantially detecting the temperature of the LEDs 1.
The LED lighting device is configured to change the current of the LED 1 to maintain the light amount substantially constant on the basis of the above characteristics. And LE
The temperature of D1 is the forward current (IF) and forward voltage (V
It detects based on the measured value of F).

This apparatus has an LED light source unit 3 in which a large number of LEDs 1 ...
And the control unit 4, and the control unit 4 has L
"Brightness adjustment switch" to adjust the brightness of ED1 ...
(UP / DOWN) 5 and "brightness setting switch" 6 for maintaining the brightness determined by adjustment are provided. And
The LEDs 1 ... Are pulse-driven as shown in the waveform of FIG.
ON DUTY is represented by TON / T. Also, as shown in FIG.
The adjustment range of the "brightness adjustment switch" (UP / DOWN) 5 can be varied in the range of ON DUTY = 30 to 70%, for example.

FIG. 4 is a circuit block diagram, in which the control unit 2
It operates at 5V DC, and the LED output of the control unit 2 drives the serial / parallel circuit of the LEDs 1 ... Including the current limiting resistors 7 ... Through the transistor Q1, and 12V DC is supplied to these serial / parallel circuits. Further, the control unit 2 detects the sum of the currents flowing through the LEDs 1 ... With the voltage generated in the resistor R1 inserted in the emitter of the transistor Q1, and also detects the voltage across the pair of series LEDs 1. The LED output terminal of the control unit 2 is PW
M control signal is output, and output table number is 0-10
It can be controlled to 0. This range corresponds to 100 steps in 0.01 increments from 0 to 1 as the ON DUTY, but the LED output control by the "brightness adjustment switch" 5 corresponds to the above range and Table No. 30 to 70. I am trying. The forward current IF of one LED 1 is obtained by dividing the voltage across the resistor R1 by its resistance value and further dividing by 5 which is the number of parallel circuits of the LEDs 1. Also, one LED
The forward voltage VF of 1 is calculated by measuring the voltage between the anode and the cathode of the set of series-connected LEDs 1 ... And dividing by 4.

In the present embodiment, in order to maintain the brightness of the LEDs 1 ...
It is good to adjust the brightness of to the desired brightness with the "brightness adjustment switch" 5 and press the "brightness setting switch" 6. Then, the temperature of LED1 ...
Even if the ambient temperature changes, the set brightness can be substantially maintained.

The characteristics of the LED 1 used are shown in FIG. 7, and the relationship between the forward voltage VF and the forward current IF at a temperature Ta of 25 ° C. is VF = a × IF + b (a and b are positive values, and in this example, a = 10, b = 1.65). In addition, the temperature characteristic of the forward voltage VF is represented by θ (V / ° C) (θ
Is a negative value), the relationship between the forward voltage VF and the forward current IF of the LEDs 1 at the temperature Ta ° C. is VF = (a × IF + b)
+ Θ × (Ta−25 ° C.), which is transformed to a temperature Ta = {(VF−a × IF−b) / θ} + 25 ° C., and the temperature Ta of the LEDs 1 ... Is obtained from VF and IF.

When the brightness of the LED 1 is adjusted and the brightness setting switch 6 is pressed, the control unit 2 causes the forward current IF and the forward voltage VF to be detected.
LE when the brightness setting switch 6 is pressed
Calculate the temperature of D1. This temperature is Tset. The control unit 2 detects (measures) the forward current IF and the forward voltage VF every 10 ms, and calculates the current temperature of the LED 1 at any time. This temperature is Tnow. Since the temperature characteristic of the luminous intensity IV shows a negative characteristic as shown in FIG. 7, the values of Tset and Tnow are compared. When Tset <Tnow, the LED1 is driven.
Increase ON DUTY, and if Tset> Tnow, L
Reduce the drive on duty of ED1. This is 10m
By repeating every s, the light amount of the LED 1 can be kept constant. These operations are shown in the flow charts of FIGS.

FIGS. 8 and 9 show another embodiment of the LED.
The temperature of 1 ... Is directly detected by a temperature sensor 11 such as a thermistor arranged near the LEDs 1.

The "brightness-lighting time characteristic" according to the present invention is greatly improved as shown in FIG. 10 as compared with the conventional "brightness-lighting time characteristic", and the change of the light amount after power-on is very small. An LED lighting device is obtained.

[Brief description of drawings]

FIG. 1 is an external view showing an embodiment of the present invention.

[Fig. 2] Same pulse drive waveform diagram

[Figure 3] Same brightness adjustment range diagram

FIG. 4 is a block diagram of the same circuit.

FIG. 5 is a first flow chart of the same.

FIG. 6 is a second flow diagram connected to XY of the first flow.

[Figure 7] LED characteristic diagram

FIG. 8 is a front view of an LED light source unit according to another embodiment.

FIG. 9 is a block diagram of the same circuit.

FIG. 10 is a comparison diagram showing the temporal characteristics of brightness of the present invention and a conventional example.

[Explanation of symbols]

The embodiment shown in FIGS. 1 to 6 has LEDs 1 ...
Control unit (microcomputer) 2 that can control the current flowing to the
LED1 having means for substantially detecting the temperature of D1 ...
It is an LED lighting device that maintains the light amount substantially constant by changing the current of the LED 1 based on the characteristic of "ambient temperature (Ta) -luminous intensity (IV)". Then, the temperature of LED1 is set to L
The detection is performed based on the measured values of the forward current (IF) and the forward voltage (VF) of ED1.

Claims (3)

[Claims] 1. An LED, a control unit capable of controlling a current flowing through the LED, and a means for substantially detecting the temperature of the LED, and the characteristic of “ambient temperature (Ta) -luminous intensity (IV)” of the LED. Based on this, an LED lighting device that changes the current of the LED to keep the light amount substantially constant. 2. The temperature of the LED according to claim 1,
LE to detect based on the measured values of forward current and forward voltage of D
D lighting device. 3. The LED temperature according to claim 1,
An LED lighting device that detects with a temperature sensor arranged in the vicinity of D.