JPH0212976A - Led driving circuit - Google Patents

Abstract

PURPOSE:To reduce power consumption which does not contribute to an optical output, to decrease power cost and to prevent a device from deteriorating due to heat generation by connecting a plurality of LEDs and one constant-current circuit in series. CONSTITUTION:Two LEDs 1, 2 emit green and red lights. The LEDs 1, 2 and one constant-current circuit 3 are connected in series. A constant-current circuit 4 is connected to the anode of the LED 1. A constant-current circuit 5 is connected to the connecting point of the LED 1 to the LED2. A transistor TR4 is connected between the connecting point of the LEDs 1, 2 and a GND. An output S1 is applied as a switching signal to the circuit 3. An output S2 is applied as a switching signal to the circuit 5. An output S3 is applied as a switching signal to the transistor TR4. When both the LEDs 1, 2 are lit, both inputs G, R are set to '1', the two LEDs 1, 2 are supplied with the constant current from the circuit 3 to be lit. When only the LED1 is lit, the input G is set to '1', and the input R is set to '0'. Thus, a constant current is supplied from the circuit 4 to the LED1, which is lit, and the it is fed to the GND through the transistor TR4.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an LED drive circuit in an LED display device used for, for example, an electronic display board on a highway.

<Conventional technology> As shown in Fig. 3, the conventional LED lighting circuit
One series resistor R was connected to each D, and this resistor R had a current limiting effect.

Furthermore, as shown in FIG. 4, there was also a method using a constant current circuit instead of a resistor.

<Problems to be Solved by the Invention> The conventional LED lighting circuit described above has a configuration in which a current limiting resistor or a constant current circuit is connected to each LED, so the power loss in the resistor or constant current circuit is increased for each LED. This has the disadvantage that more than half of the power of the entire display device is consumed by this resistor or constant current circuit.

The present invention has been made in view of the above circumstances, and its purpose is to provide an LED with reduced power consumption that does not contribute to light emission output.
Another object of the present invention is to provide a driving circuit.

Means for Solving the Problems> In order to achieve the above object, an LED drive circuit according to the present invention includes a first circuit in which a plurality of LEDs and one constant current circuit are connected in series; A first switching circuit that switches current supply from a constant current circuit to a plurality of LEDs in one circuit; a second circuit in which a constant current circuit is connected to each of the plurality of LEDs; The circuit includes a second switching circuit that switches the current supply from the constant current circuit to the LED.

<Function> The LED drive circuit according to the present invention supplies current from one constant current circuit to the plurality of LEDs in the first circuit when lighting all of the plurality of LEDs, and when lighting the LEDs individually. In the second circuit, a constant current circuit supplies current to the LEDs individually.

<Example> FIG. 1 shows the configuration of an LED drive circuit of this example.

The two LEDs 0 and 2 emit green and red light, respectively. These two LEDIs 2 and one constant current circuit 3 are connected in series. Constant current circuit 4 is connected to the anode of LEDl.

The constant current circuit 5 is connected to a contact point between the LEDI and the LED 2. Transistor TR4 is LEDI, 2
is connected between the connection point and GND. logic circuit 6
has the following truth table relationship between the inputs G and R and the output S l+ S 2 + S3.

The output S is given to the constant current circuit 3 as a switching signal. The output S2 is given to the constant current circuit 5 as a switching signal. The output S3 is a transistor TR,
is given as a switching signal.

The operation will be explained below.

First, when lighting both LEDs I and 2, by setting both inputs G and R to "1", the output S becomes "0" and the transistor TR of the constant current circuit 3 is turned on. , the two LEDIs 2 are supplied with a constant current from the constant current circuit 3 and are turned on.

At this time, the output S2 is "1" and the output S3 is "0", so the transistor TR2 of the constant current circuit 4, the transistor TR3 and the transistor TR of the constant current circuit 5 are in an off state.

When these two LEDs 2 are lit at the same time, the circuit consumes maximum power, but in this case, the only power that does not contribute to the light output is the power consumed by the emitter resistance of transistor TR. . Regarding this point, conventionally, a constant current circuit is required for each LED, so
Reactive power that does not contribute to optical output is doubled.

Next, to turn on only LEDl, set input G to “1”
, when the human power R is “O”, the transistors TR2, TR
, is on, transistor TR,.

TR3 is turned off, a constant current is supplied from the constant current circuit 4 to LEDl, lights up LEDl, and then flows to GND via transistor TR. When lighting only LED2, input G is set to "O" and input R is set to "1", only transistor TR1 is turned on, and a constant current flows from constant current circuit 5 to GND through LED2.Two LEDs
When turning off both I and 2, if both inputs G and R are set to "0", the transistors TR, , TR2゜TR
,,TR, are all turned off.

According to the lighting circuit configured as described above, when a constant current is caused to flow through the LED, power consumption that does not contribute to light output can be minimized. For example, if the forward voltage of the LED is 2■ and the voltage required for the constant current circuit is 2■, the power required to light up two LEDs is (11 In the present invention, see Figure 2. Then, 21+21+
2 I=61 (2) In the conventional method, referring to Figure 5, 41+4
1=8I. Therefore, in the present invention, power consumption is reduced by 25% from .

In the above embodiment, the number of LEDs is two, but the number of LEDs connected in series is not limited to two, and the same effect can be obtained even if the number of LEDs is further increased.

<Effects of the Invention> As explained above, in the present invention, a plurality of LE
Since D and one constant current circuit are connected in series, power consumption that does not contribute to optical output can be reduced, and effects such as reduction in power cost and prevention of device deterioration due to heat generation can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the circuit configuration of an embodiment of the present invention, FIG. 2 is a diagram explaining the invention in detail, FIGS. 3 and 4 are diagrams showing the configuration of a conventional example, and FIG. 5 is a conventional example. It is a figure explaining the effect|action. 1, 2 ・ ・ ・ LED 3.4.5... Constant current circuit 6... Logic circuit TR+, TRz, TRi, TRa... Transistor

Claims (1)

[Claims] A first circuit in which a plurality of LEDs and one constant current circuit are connected in series, and a plurality of LEDs in this first circuit.
The first switch switches the current supply from the constant current circuit to
a switching circuit, a second circuit in which a constant current circuit is connected to each of the plurality of LEDs, and a second switching circuit that switches current supply from the constant current circuit to the LEDs in the second circuit. An LED drive circuit characterized by: