JPH0567810A - Drive circuit for light emitting diode - Google Patents

Abstract

PURPOSE:To reduce power loss to suppress electric power consumption by connecting two or more circuit blocks in series, each block being constituted by connecting one end of a light emitting diode with one end of a bypassing circuit and by making a connection with a changeover circuit which permits a current to flow to the light emitting diode side or to the bypassing circuit side. CONSTITUTION:The fed voltage is -24V and 10 light emitting diodes are controlled. A circuit block is constituted by a limiting resistor 1 which limits the current flowing in the entire circuit, a switch 2 which dims all light emitting diodes and switches 20, 21,...29 which select to which the current is permitted to flow, light emitting diodes 30, 31,...39 or bypassing resistors 10, 11,...19. Ten blocks are connected in series. The light emitting diode 39 is turned on by changing the switch 29 over to the light emitting diode side. And it is dimed by changing the switch over to the resistor 19 side. This applies to other light emitting diodes, too. As a result, power consumption is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode drive circuit.

[0002]

2. Description of the Related Art A typical circuit of a conventional light emitting diode drive circuit is to connect a resistor 5 and a switch 7 for current limiting in series with a light emitting diode 6 and open / close the switch 7 as shown in FIG. Was controlling the lighting / extinction of the light emitting diode. Although a switch will be described here for simplification, a transistor or an integrated circuit is generally used in many cases. Typical power supply voltage at that time is shown in Fig. 3.
+ 5V as in the example.

Here, the current flowing through the light emitting diode 6 is 10 mA, and the voltage drop of the light emitting diode 6 at that time is 2 mA.
Assuming that V, a voltage of 5V-2V = 3V is applied to the resistor 5, and it can be seen that the required resistance value is 3V / 10mA = 300Ω. In addition, power consumption is 5V × 10mA = 50m
W, 3V x 10mA which is the consumption of resistor 5
= 30 mW is a loss. That is, 30 mW ÷ 50 mW ×
Consider, for example, a telephone with a large number of light emitting diodes, where 100 = 60% power is lost. This telephone is supplied with a voltage of -24V from the main control unit, and has a built-in DC-DC converter from -24V to + 5V.
Let's make. The conversion efficiency of the DC-DC converter is 50%, and considering the case of lighting 10 light emitting diodes, the power consumption on the +5 V side is 50 mW × 10 = 50.
0mW, therefore 500mW ÷ 50% = 1 at -24V side
The power consumption is 000 mW. On the other hand, since the power consumed by the light emitting diode is 2V × 10 mA × 10 = 200 mW, 1000 mW−200 mW = 800 mW, that is, 800 mW ÷ 1000 mW × 100 = 80% of the power is wasted.

In this example, the power consumption is increased due to the efficiency of the DC-DC converter, but even if the light emitting diode is directly driven on the -24V side, it is not improved. Because a voltage of 24V and a current of 10mA are required for each light emitting diode, 1
The power consumption at 0 is 24V × 10mW × 10 = 2400
This is because it becomes mW and increases instead.

[0005]

As described above, the conventional light emitting diode drive circuit has a problem that the loss in the current limiting resistor is large, which uses a DC-DC converter to obtain the voltage of the drive circuit. It was especially remarkable when it did.

An object of the present invention is to provide a light emitting diode drive circuit that reduces power loss and suppresses power consumption.

[0007]

In the light emitting diode drive circuit of the present invention, one end of a bypass circuit is connected to one end of the light emitting diode, and the other end of the bypass circuit and the other end of the light emitting diode are bypassed to the light emitting diode side. Connect two or more circuit blocks in series that are connected to a switching circuit that switches between which side the current flows to, and connect one end to one of the power sources via a switch to cut off all current. , The other is connected to the other end of the power source through a resistor that controls the energizing current. In addition, two or more circuit blocks, each of which is formed by connecting a switching circuit that bypasses a current flowing through the light emitting diode in parallel with the light emitting diode, are connected in series, and one end of the power source is connected through a switch for cutting off all the current. And the other end is connected to the other end of the power source via a constant current circuit for controlling the energizing current.

[0008]

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

FIG. 1 is a circuit diagram showing an embodiment of the present invention. The power supply voltage is -24V and it is assumed that 10 light emitting diodes are controlled, and the limiting resistor for the current flowing through the entire circuit 1
And a switch 2 for reducing all the light emitting diodes,
A circuit block composed of a switch 20 (21, ... 29) for selecting which of the light emitting diode 30 (31, ... 39) or the bypass resistor 10 (11, ... Connected. In the actual circuit, analog switches, optical MOSFET relays, etc. are assumed, but here, for simplicity, switches will be described. To turn on the light emitting diode 39, switch 29
The resistor 19 is used to bring the
To the side of. The same applies to other light emitting diodes.

Next, calculation will be performed. The current and voltage drop flowing through the light emitting diode are the same as in the conventional example described in the related art.
If the current is 10 mA and 2 V, the same voltage drop will occur when the switches are switched to the resistors 10 to 19, so that the resistance 1
0 to 19 may be set to 2V / 10 mA = 200Ω. The voltage applied to the resistor 1 is 24V-2V × 10 = 4V.
Therefore, the resistance 1 may be 4V / 10mA = 400Ω. At this time, the power loss in the resistor 1 is 4 V × 10 mA = 4
0mW, power consumption of the whole circuit is 24V x 10 from 1 to 10 LEDs
mA = 240 mW.

From the above, the power loss when 10 light emitting diodes are turned on at maximum is 4 due to only the loss in the resistor 1.
At 0 mW, the ratio is 40 mW / 240 mW = 17%, which is much improved from 80% of the conventional example. In addition, the power consumption is significantly reduced to 240 mW, compared to 1000 mW in the conventional example.

Next, a second embodiment of the present invention will be described with reference to FIG.

In FIG. 2, the constant current circuit 3 is for limiting the current flowing in this circuit, and the switch 4 is for deactivating all the light emitting diodes. It can be considered that one circuit block in this example includes a light emitting diode 50, a switch 40 connected in parallel with the light emitting diode 50, and a bypass circuit formed by a resistance of 0Ω. As in the first embodiment described above, 10 circuits are connected in series to form a circuit. In this example, when turning on the light emitting diode 50, the switch 40 is turned off, and when reducing the fire, it is turned on. Also in this example, the power supply voltage is −24 V, the current flowing through the light emitting diode and the voltage drop there are 10 mA and 2 respectively.
If the constant current value of V and the constant current circuit 3 is 10 mA, the power consumption when the light emitting diode is lit is 24 V × 10 mA = 240 mW regardless of the number of lighting, and the same effect as the first embodiment can be obtained. Be done.

[0014]

As described above, the present invention has an effect that power loss can be suppressed by reducing loss power by connecting a plurality of light emitting diode drive circuit blocks in series.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a conventional example of a light emitting diode drive circuit.

[Explanation of symbols]

 1,5 Resistance for current limitation 2,4,7,20 to 29,40 Switch 3 Constant current circuit 6,30 to 39,50 Light emitting diode 10 to 19 Resistor

Claims (2)

[Claims] 1. A switching circuit in which one end of a bypass circuit is connected to one end of a light emitting diode, and the other end of the bypass circuit and the other end of the light emitting diode are switched between the light emitting diode side and the bypass circuit side. Two or more circuit blocks connected in series are connected in series, one end of which is connected to one of the power supplies via a switch for cutting off the total current, and the other of which is connected via a resistor for controlling the energizing current. A light-emitting diode drive circuit, which is configured to be connected to the other end of a power supply. 2. A circuit block formed by connecting a switching circuit for bypassing a current flowing through the light emitting diode in parallel with the light emitting diode is connected in series in two or more circuit blocks, and a switch for cutting off all the current is provided at one end. Is connected to one of the power sources, and the other is connected to the other end of the power source via a constant current circuit for controlling the energizing current.