JP3148908B2 - Light emitting diode drive circuit - Google Patents

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 driving circuit used for a display device driven by a power source such as a primary battery or a secondary battery.

[0002]

2. Description of the Related Art Conventionally, a light emitting diode driving circuit is generally configured to perform only a lighting operation of a light emitting diode, and a switch for turning on and off a power supply is separately provided. In addition, there is no example in which a switch operation is performed by attaching and detaching the light emitting diode itself even in a device using a detachable bead ball or a light emitting diode. For example, a light-emitting diode drive circuit used for an operation panel of an automobile or an indicator of an audio device has only a function of blinking a light-emitting diode and lighting characters and pictures, such as an outdoor advertising indicator and a destination indicator. ing.

[0003] Further, in a disaster prevention device such as a small construction marker light to which a light emitting diode can be attached and detached and a fire hydrant position indicator lamp for outdoor use, a waterproof mechanical switch or a magnetic switch is used to provide a waterproof structure. This is expensive, and the structure of the device is complicated due to the mounting of the switch.

[0004]

Therefore, many light emitting diodes of such a device are fixed to a socket or the like so as to change its color or size or to enable compatibility with a miniature bulb. . If the power can be turned on and off by attaching and detaching the light emitting diode, it is not necessary to newly provide a power switch. In particular, among the above applications, those installed outdoors need to have improved waterproofness. Also,
If the power supply is a battery as in the above-described apparatus and there is a problem in the reliability of a switch for turning on and off a separately provided power supply, the light emitting display function is stopped due to overdischarge or short circuit of the battery. In particular, in a disaster prevention and crime prevention monitoring device outdoors, turning off the light emitting diode due to a power supply failure may cause a serious accident.

An object of the present invention is to solve the above-mentioned problems and to provide a highly reliable light emitting diode driving circuit which does not require a separate power switch.

[0006]

In order to achieve the above object, a light emitting diode driving circuit according to a first means of the present invention comprises:
A pair of output terminals, a light emitting diode detachably connected to the output terminal, a constant current circuit for supplying a constant current to the light emitting diode, a voltage detecting circuit for detecting a voltage across the light emitting diode, A switch circuit for receiving or outputting an output of the detection circuit to connect or disconnect a power supply.

Further, the constant current circuit in the first means is provided with a control terminal capable of stopping light emission of the light emitting diode by an external DC voltage.

Further, the light-emitting diode driving circuit according to the second means detects a short-circuit or an over-discharge state of the battery as the main power supply, the battery as the auxiliary power supply, and the battery as the main power supply for lighting the light-emitting diode. A voltage detection circuit, a semiconductor switch element for switching to a battery as the auxiliary power supply according to a signal of the voltage detection circuit, and the semiconductor switch element for switching to a battery as the auxiliary power supply for reducing current consumption when there is no load And a control terminal for cutting off the bias.

[0009]

According to the structure of the first means of the present invention, a light emitting diode is detachably provided at the output terminal, and the light emitting diode is separated from the output terminal during product stock or transportation.
To connect the light emitting diode to the output terminal only when used,
There is no need to provide a separate switch in the light emitting diode drive circuit, and it is possible to prevent a decrease in battery capacity, a short circuit, overdischarge, and the like due to insufficient reliability of the switch during product inventory or transportation.

Further, according to the configuration of the second means of the present invention,
Even if an abnormality occurs in the battery as the main power supply, the battery is automatically switched to the auxiliary power supply, so that the lighting of the light emitting diode is not interrupted and the number of maintenance operations can be reduced.

Further, by connecting the first means and the second means of the present invention to each other, it is possible to realize a light emitting diode driving circuit having a function of switching the power supply by the light emitting diode and a function of switching between the main power supply and the auxiliary power supply. .

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A light emitting diode driving circuit according to an embodiment of the present invention will be specifically described with reference to the drawings.

(Embodiment 1) FIG. 1 shows a light emitting diode driving circuit according to the first means of the present invention. In FIG. 1, a power supply terminal 1a, to which power from a battery 1 serving as a power supply is applied,
A constant current circuit 3 for supplying a constant current to the light emitting diode 2 serving as a load connected to the output terminals 2a and 2b connected to the output terminals 1b and a voltage detecting circuit 4 for detecting a voltage across the light emitting diode 2 are connected in parallel. Further, the voltage detection circuit 4 is connected to a switch circuit 5 which is a semiconductor switch or a relay which is turned on / off by the output of the voltage detection circuit 4. Also,
The terminals 7a and 7b are connected to the terminal 2 shown in FIG. 2 when the LED driving circuit of Embodiment 1 (with the battery 1 removed) is connected to the LED driving circuit of Embodiment 2 described later.
4 and 14b.

The light emitting diode 2 is connected to output terminals 2a, 2a.
b, the power supply applied to the power supply terminals 1a and 1b is turned off, or the constant current circuit 3 stops operating by the control terminal 6 and the voltage of the output terminals 2a and 2b becomes zero. A terminal 8 for biasing a voltage required for operating the voltage detection circuit 4 is connected to the output terminal 2a so that the switching function of the voltage detecting circuit 4 can be performed.

The constant current circuit 3 has a control terminal 6 which can sink the base current of the transistor 9 connected between the power supply terminal 1a and the voltage detection circuit 4 with a constant current and stop this operation by a DC signal. . The transistor 9 supplies the amplified constant current to the light emitting diode 2 from the power supply terminal 1a.

Next, the operation of the light emitting diode driving circuit of the first embodiment configured as described above will be described using the light emitting diode current-voltage characteristics shown in FIG. 1 and FIG.

Since the base current of the transistor 9 is controlled to be constant by the constant current circuit 3, a collector current that is approximately equal to the product of the base current and the amplification factor of the transistor 9 is connected to the output terminals 2a and 2b. The light is supplied to the light emitting diode 2. At this time, the voltage generated at the output terminals 2a and 2b is naturally determined by the current-voltage characteristics of the light emitting diode as shown in FIG. 3, for example. According to FIG. 3, for example, a yellow light-emitting diode has an operating current of about 20 mA and is 2.1.
5V, orange light emitting diode is 19.2 mA at 1.92 mA.
A voltage of 8V is generated. Therefore, if the detection voltage of the voltage detection circuit 4 is set to be equal to or higher than the voltage generated at the light emitting diode 2, the voltage detection circuit 4
While connected to a and 2b, the switch circuit 5 is turned on by detecting a low level.

When the light emitting diode 2 is removed from the output terminals 2a and 2b, the collector current of the transistor 9 becomes zero, and the voltage at the output terminals 2a and 2b becomes equal to the power supply voltage. Therefore, the voltage detection circuit 4 can detect a high level. However, for the detection of the high level, the detection voltage of the voltage detection circuit 4 must be set to be equal to or smaller than the power supply voltage. The switch circuit 5 is turned on and off in response to the DC signal of the voltage detection circuit 4, and supplies the power supply voltage of the power supply terminals 1a and 1b to the terminals 7a and 7b.

Further, the control terminal 6 of the constant current circuit 3 serves to interrupt the base current of the transistor 9 by biasing the constant current circuit 3 with a DC voltage or short-circuiting the constant current circuit 3. Thus, the light emitting diode 2 can be turned off, and the control terminal 6 can be turned on and off by biasing the control terminal 6 with a pulse voltage.

Therefore, by attaching and detaching the light emitting diode 2 to and from the output terminals 2a and 2b, the power can be turned on and off, and a circuit that does not require a power switch other than the light emitting diode can be configured. Further, the light emitting diode 2 is controlled by the constant current circuit 3.
Can maintain a constant luminance, so that stable visibility can be expected.

The constant current circuit 3 of the first embodiment may be constituted by using a transistor, a field effect transistor, an IC, or the like, and the voltage detection circuit 4 may be constituted by using a transistor, a field effect transistor, an IC, or the like. You may comprise.

(Embodiment 2) FIG. 2 shows a light emitting diode driving circuit according to the second means of the present invention. In FIG. 2, a semiconductor switch element 12 operated by an output of the voltage detection circuit 11 is connected to a voltage detection circuit 11 for detecting a short circuit or overdischarge of a battery (primary battery or secondary battery) 10 of a main power supply. 12 is connected to a semiconductor switch element 15 for supplying electricity to the terminals 14a and 14b of the battery 10 connected to the power terminals 13a and 13b.

When the voltage detection circuit 11 is outputting, the middle point 18 of the resistor 16 and the resistor 17 is connected to the diode 19.
The semiconductor switch element 22 is connected so as to be biased only in one direction, and turns on and off a battery (primary battery or secondary battery) 21 of an auxiliary power supply connected to the terminals 20a and 20b. It turns on when the voltage detection circuit 11 outputs so that the semiconductor switch element 15 turns off, and the terminals 13a, 13b and 14
a and 14b are electrically connected to each other. In short, this indicates that the semiconductor switch element 15 and the semiconductor switch element 22 are connected so as to operate in opposition to each other with the output of the voltage detection circuit 11. Further, a semiconductor switch element 23 capable of forcibly turning off the semiconductor switch elements 15 and 22 irrespective of the output of the voltage detection circuit 11
And the control terminal 24 are connected.

Therefore, even if the battery 10 of the main power supply is short-circuited or overdischarged, power is supplied from the battery 21 of the auxiliary power supply.
When a light emitting diode or the like is connected to the terminals 24 and 14b for use in the light emitting diode control circuit of the second embodiment, the operation stop of the light emitting diode or the like can be prevented.

By turning off the semiconductor switch element 23, the operation of the light emitting diode connected to the terminals 24 and 14b can be stopped.

The output terminals 7a and 7b of the light emitting diode drive circuit of the first embodiment are connected to the semiconductor switch element 2 of the second embodiment.
3 is input to the terminals 24 and 14b as the control signal of the third embodiment.
When the light emitting diode 2 is removed from the output terminals 2a and 2b, the light emitting diode drive circuit of the second embodiment stops operating,
At the same time, the operation of the light emitting diode drive circuit of the first embodiment can be stopped. As a result, the current consumption of the light emitting diode driving circuit of the first embodiment and the light emitting diode driving circuit of the second embodiment can be substantially eliminated. Next, the operation of the light emitting diode drive circuit according to the second embodiment will be described below.

In the second embodiment, the short circuit or overdischarge of the battery (primary battery or secondary battery) 10 as the main power supply connected to the terminals 13a and 13b is detected by the voltage detection circuit 11. The detection circuit 11 outputs a high level to turn on the semiconductor switch element 12 and the semiconductor switch element 15, and at the same time, biases the middle point 18 of the resistor 16 and the resistor 17 via the diode 19 to bias the semiconductor switch element 2
Turn 2 off. At this time, the battery 21 as an auxiliary power supply connected to the terminals 20a and 20b is separated from the light emitting diode drive circuit. When the battery 10 of the main power supply is short-circuited or over-discharged and falls below the detection voltage of the voltage detection circuit 11, the voltage detection circuit 11 outputs a low level, and the semiconductor switch element 12 is immediately turned off. At the same time, the bias at the midpoint 18 between the resistors 16 and 17 is eliminated and the semiconductor switch element 22
Turns on.

The semiconductor switch element 23 stops the output of the main power supply and the auxiliary power supply to the terminals 14a and 14b regardless of the operation of the voltage detection circuit 11. At this time, the diode 19 prevents the semiconductor switch element 22 from being turned on via the output terminal of the voltage detection circuit 11.

By connecting the terminals 7a and 7b of the light emitting diode drive circuit of the first embodiment to the terminals 24 and 14b as control signals for the semiconductor switch element 23 and removing the light emitting diode 2 from the output terminals 2a and 2b, FIG. The outputs of the terminals 14a and 14b shown in the figure are turned off, and the light emitting diode drive circuit of the first embodiment also stops when the power is turned off.

Therefore, the light emitting diode driving circuit of the first embodiment and the light emitting diode driving circuit of the second embodiment are connected to each other, so that a light emitting diode having a function of switching between a main power supply and an auxiliary power supply and a function of switching a power supply by the light emitting diode. A drive circuit can be realized. In particular, the present invention is effective in outdoor equipment in which power supply cannot be easily replaced, for example, fire prevention equipment such as a fire hydrant position indicator light, construction sign light, and a monitoring device that requires continuous lighting of a light emitting diode.

The voltage detection circuit 11 according to the second embodiment may be constituted by using a transistor, a field effect transistor, an IC, or the like. The semiconductor switch element 12, the semiconductor switch element 15, and the semiconductor switch element 22 A transistor, a field-effect transistor, an IC, a relay, or the like may be used. In addition, as a battery as a main power supply and an auxiliary power supply in the second embodiment, a dry battery, a mercury battery, a lithium battery, or the like can be used as a primary battery. In the case of a secondary battery, a nickel-cadmium battery, a nickel-metal hydride storage battery, a lead storage battery, and a lithium secondary battery can be used. In particular, miniaturization is possible by using a coin-shaped lithium battery. Further, if the secondary battery is used as a main power source and a solar battery is used as a means for charging the secondary battery, a power source and a light emitting diode driving circuit that do not require maintenance can be realized.

[0032]

As is apparent from the above description, the light emitting diode driving circuit of the present invention has the following effects. (1) Since the power can be turned on and off by the light emitting diode, it is not necessary to newly provide a power switch in a device that outputs the light of the light emitting diode, and particularly in an outdoor device, a structure advantageous in terms of waterproofing can be realized. (2) A battery (primary battery or secondary battery) as a main power supply for lighting a light emitting diode or a short-circuit or an overdischarge state is detected by a voltage detection circuit and switched to a battery (primary battery or secondary battery) as an auxiliary power supply. By doing so, the light emitting diode can be turned on without interruption even if the main power supply becomes abnormal. (3) By connecting the light emitting diode driving circuit (with the battery removed) according to claim 1 and the light emitting diode driving circuit according to claim 3 when the light emitting diode is removed from the output terminal, the light emitting diode driving circuit according to claim 3 is connected. Since the switching operation between the main power supply and the auxiliary power supply of the light emitting diode drive circuit can be stopped, the current consumption of the circuit can be extremely reduced. If a battery (primary or secondary battery) is used as the main power supply, it is in stock or transported. It is possible to prevent a remarkable decrease in the battery capacity inside.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a light emitting diode drive circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a light emitting diode drive circuit according to the second embodiment.

FIG. 3 is a graph showing current-voltage characteristics of a light emitting diode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery (power supply) 2 Light emitting diode 2a, 2b Output terminal 3 Constant current circuit 4, 11 Voltage detection circuit 5 Switch circuit 10 Battery 12, 15, 22, 23 as main power supply Semiconductor switch element 21 Battery as auxiliary power supply 24 Control Terminal

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Mikio Murosono 1006 Kazuma Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. (56) References JP-A-5-199667 (JP, A) JP-A-2- 73417 (JP, A) Fully open 1983-87369 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G09F 13/20 H01H 9/54 H03K 17/78 H02J 7/00

Claims (3)

(57) [Claims] 1. A pair of output terminals, a light emitting diode detachably provided at the output terminal, a constant current circuit for supplying a constant current to the light emitting diode, and a voltage detecting circuit for detecting a voltage across the light emitting diode. And a switch circuit for connecting or disconnecting a power supply in response to the output of the voltage detection circuit. 2. The light emitting diode driving circuit according to claim 1, wherein the constant current circuit has a control terminal for stopping light emission of the light emitting diode. 3. A battery as a main power supply, a battery as an auxiliary power supply, a voltage detection circuit for detecting a short-circuit or an over-discharge state of the battery as the main power supply for lighting a light emitting diode,
The semiconductor switch element for switching to the battery as the auxiliary power supply according to the signal of the voltage detection circuit, and the bias of the semiconductor switch element for switching to the battery as the auxiliary power supply for reducing current consumption when there is no load is cut off. A light emitting diode drive circuit comprising a control terminal.