JP2000260578A - Led lighting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong the service lives of LEDs and to enhance the light output of the LEDs. SOLUTION: This LED lighting circuit is provided with a rectifying circuit 2 for rectifying inputted alternating-current power, a resistor 3 and a Zener diode 4 series-connected between the positive-side (+) power source of pulsating- current power obtained by the rectifying circuit 2 and the ground, and a transistor 5 with a base connected between the resistor 3 and the Zener diode 4. LEDs 1 are connected between a collector of the transistor 5 and the positive-side power source, and a resistor 6 is connected between an emitter of the transistor 5 and the ground.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an LED lighting circuit.

[0002]

2. Description of the Related Art For example, a lighting system employed in a light emitting / illuminating device having a plurality of LEDs, such as an LED display device or an LED traffic light, employs a pulsating current obtained by simply rectifying an AC power supply as a DC power supply. There is a method of lighting.

As an example, as shown in FIG. 4, a rectifier circuit 22 for rectifying an alternating current from an AC power supply 7 into a pulsating flow is provided, and the rectifier circuit 22 includes a plurality of LEDs 1... An LED lighting circuit that is connected in series may be used.

[0004]

By the way, according to the LED lighting circuit shown in FIG. 4, the current flowing through the LED changes with respect to the rectified power supply voltage (pulsating current) as shown in the waveform diagram of FIG. And the peak value also increases, there are the following problems. (1) Since the current waveform ratio (= effective value / average value) increases, the junction temperature (junction temperature) of the LED greatly fluctuates, and the temperature fluctuation tends to cause deterioration of the chip bonding portion. As a result, the life of the LED is shortened.

[0005] The junction temperature is the sum of the internal temperature rise and the ambient temperature due to Joule heat generated when a current flows through the junction of the element. (2) Since the ratio of the current fluctuation is larger than the ratio of the fluctuation of the AC power supply, the fluctuation of the light output (brightness) is large. Also, if the brightness is designed to ensure the required brightness at the lowest power supply voltage in consideration of fluctuations in the AC power supply, a large current will flow through the LED at normal voltage, and the life of the LED will also be reduced in this case. Be shorter. (3) Since a large current is taken when the peak value of the power supply voltage is maximum, the peak (top) of the power supply voltage waveform is crushed, and the disturbance of the voltage waveform adversely affects other electric devices. (4) The peak value of the current increases, and the LED
And the junction temperature rises as a result. Therefore, the light output decreases due to the temperature-light output characteristics of the LED. Further, the light output also decreases from the point that the current waveform ratio (= effective value / average value) increases.
That is, the LED has a characteristic that the light output efficiency is reduced when the peak value of the flowing current is high.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems.
It is an object of the present invention to provide an LED lighting circuit capable of improving the light output of D.

[0007]

In order to achieve the above object, an LED lighting circuit according to the present invention is a lighting circuit for lighting an LED using a pulsating current obtained by rectifying an AC power supply as a DC power supply, A rectifier circuit for rectifying the input AC power supply, a resistor and a Zener diode connected in series between the + side power supply of the pulsating power supply obtained by the rectifier circuit and the ground, and a resistor between the resistor and the Zener diode. A transistor having a base connected thereto, wherein the LED is connected between the collector of the transistor and the + power supply, and a resistor is connected between the emitter of the transistor and ground.

The LED lighting circuit according to the second aspect of the present invention comprises:
A lighting circuit for lighting an LED using a pulsating current obtained by rectifying an AC power supply as a DC power supply. A zener diode and a resistor connected in series, a transistor having a base connected between the zener diode and the resistor, an LED connected between the collector of the transistor and ground, and an emitter of the transistor And a positive side power supply.

According to the LED lighting circuit according to the first and second aspects of the present invention, the transistor, the zener diode and the
Since a constant current circuit is composed of two resistors, LE
The peak value of the current flowing through D is small and constant. In addition, even if the AC power supply fluctuates, the current fluctuation can be small.

[0010]

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

FIG. 1 is a diagram showing a circuit configuration of an embodiment of the present invention. The LED lighting circuit shown in FIG.
Rectifier circuit 2 that obtains pulsating power by full-wave rectification of AC from
And a resistor 3 and a Zener diode 4 connected in series between the + side (+ V) power supply of the pulsating power supply obtained by the rectifier circuit 2 and the ground, and between the resistor 3 and the Zener diode 4 A transistor 5 connected to a base 5B, and a collector 5C of the transistor 5;
A plurality of LEDs 1... 1 are connected between the power supply and the + (+ V) power supply. A resistor 6 is connected between the emitter 5E of the transistor 5 and the ground, and the transistor 5, the Zener diode 4, and the two resistors 3,
6 forms a constant current circuit.

In the above circuit configuration, when the power supply voltage (pulsating current) rectified by the rectifier circuit 2 rises from 0 (FIG. 3) and exceeds the Zener voltage of the Zener diode 4, the voltage of the emitter 5E of the transistor 5 becomes , The voltage of the base 5B to the emitter 5E (for example, about 0.7V), the voltage of the emitter 5B is a little lower than the Zener voltage, but a constant value. Here, since the resistor 6 is connected between the emitter 5E and the ground, the resistor 6
Is constant. Thus, as shown in FIG. 3, the current flowing through the LEDs 1... 1 has a small peak value and is constant, and the current waveform is substantially a square wave. Moreover, the peak value of the current flowing through the resistor 6 is kept substantially constant without being affected by the fluctuation of the AC power supply.

FIG. 2 is a diagram showing a circuit configuration of another embodiment of the present invention. The LED lighting circuit shown in FIG. 2 includes a rectifier circuit 12 that obtains a pulsating power source by full-wave rectifying the alternating current from the AC power source 7, and a + (+ V) power source of the pulsating power source obtained by the rectifying circuit 12 and the ground. A resistor 15 having a base 15B connected between the Zener diode 14 and the resistor 13, and a collector 15C of the transistor 15 and a ground. Between multiple LEDs 1 ...
1 is connected. A resistor 16 is connected between the emitter 15E of the transistor 15 and the + side (+ V) power supply. The transistor 15, the Zener diode 14, and the two resistors 13 and 16 form a constant current circuit. I have.

In the LED lighting circuit shown in FIG. 2 as well, the operation of the resistor 1 is performed in the same manner as in the embodiment of FIG.
As a result of the current flowing through the LED 6 being constant, the peak value of the current flowing through the LEDs 1... 1 is small and constant. Moreover, the peak value of the current flowing through the resistor 16 is kept substantially constant without being affected by the fluctuation of the AC power supply.

In the above embodiment, a plurality of LEs
Although an example in which D is connected in series is shown, the present invention is not limited to this, and the present invention is also applied to a lighting circuit for lighting one LED or a lighting circuit for lighting a plurality of LEDs connected in parallel. Applicable.

[0016]

As described above, according to the LED lighting circuit according to the first and second aspects of the present invention, the transistor is provided between the LED and the rectifier circuit for rectifying the AC power into a pulsating current to obtain the DC power. , A constant current circuit composed of a zener diode and two resistors, the following effects can be achieved. (1) Since the circuit is a constant current circuit, the peak value is constant, the fluctuation in junction temperature is reduced, and the life of the LED is extended. (2) The peak value is constant with respect to power supply fluctuations, and current fluctuations due to power supply fluctuations can be designed to be small, thereby extending the life of the LED. (3) Since the current flowing through the LED is substantially a square wave, the influence on the power supply voltage waveform is reduced, and the possibility that other electric devices are adversely affected is reduced. It is also possible to correct the load current of other general capacitor inputs to improve the power supply voltage waveform. (4) Since it is a constant current circuit, even if the average value of the current is the same as the average value of the current in the conventional LED lighting circuit, the peak value of the current can be made smaller and more constant than in the conventional lighting circuit. As a result, the maximum junction temperature of the LED is reduced. As a result, the decrease in light output due to temperature is smaller than in the conventional case. When the light output is the same as the conventional one, the average current value can be kept low.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of an LED lighting circuit according to the present invention.

FIG. 2 is a circuit configuration diagram of another embodiment of the LED lighting circuit of the present invention.

FIG. 3 is a graph showing both a power supply voltage waveform diagram and a current waveform diagram of the LED lighting circuit shown in FIG.

FIG. 4 is a circuit configuration diagram of a conventional LED lighting circuit.

FIG. 5 is a graph showing both a power supply voltage waveform diagram and a current waveform diagram of a conventional LED lighting circuit.

FIG. 6 is a graph showing an example of temperature characteristics of light output of an LED.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 LED 2,12 Rectifier circuit 3,13 Resistor 4,14 Zener diode 5,15 Transistor 5B, 15B 5C, 15C 5E, 15E 6 Resistor 7 AC power supply

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hirokazu Iwane 36, Teradashinike, Joyo-shi, Kyoto Seika Electric Co., Ltd. F-term (reference) 3K073 AA16 AA87 CG45 CJ18

Claims (2)

[Claims] 1. A lighting circuit for lighting an LED using a pulsating current obtained by rectifying an AC power supply as a DC power supply, comprising: a rectifying circuit for rectifying an input AC power supply; A resistor and a zener diode connected in series with the ground; and a transistor having a base connected between the resistor and the zener diode.
An LED having an ED connected thereto and a resistor connected between the emitter of the transistor and ground.
Lighting circuit. 2. A lighting circuit for lighting an LED using a pulsating current obtained by rectifying an AC power supply as a DC power supply, comprising: a rectifying circuit for rectifying an input AC power supply; A Zener diode and a resistor connected in series to the ground, a transistor having a base connected between the Zener diode and the resistor, and an LED between the collector of the transistor and the ground.
And a resistor connected between the emitter of the transistor and the + side power supply.
Lighting circuit.