JP2004241908A - Light beacon led driving circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light beacon LED driving circuit which can stabilize LED light emission power, widen the usable voltage width of a forward voltage VFM of a light beacon LED, and reduce the cost of an LED by improving the yield. <P>SOLUTION: A driving circuit 11 for an LED 11 for a light beacon comprises a clamp circuit 14 which clamps an LED light emission signal pulse to a fixed voltage amplitude level, a transistor which drives the LED 11, and a load resistance 13 interposed between the emitter of the transistor and the ground. The LED light emission signal clamped to the fixed voltage is inputted to the base of the transistor to determine its emitter voltage and a current determined by the load resistance 13 is supplied to the LED 11 in timing to pulses of the LED light emission signal. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical beacon LED driving circuit that conveys information on traffic congestion or regulation to a car navigation device or the like.
[0002]
[Prior art]
Recently, information collected by vehicle detectors and remote control cameras managed by prefectural police and road managers is sent to the VICS Center via the Japan Road Traffic Information Center, where information is edited and installed in various locations. VICS in-vehicle equipment consisting of radio beacons, optical beacons, FM character multiplex tuners installed in in-vehicle equipment such as car navigation etc. VICS that receives and displays with characters and figures has become widespread. Further, a VICS information request is made by transmitting a signal from the VICS in-vehicle device to the VICS roadside device.
[0003]
In the conventional VICS in-vehicle device, the optical beacon is a communication method using near infrared, and the transmission area before and after the optical beacon is used as the transmission area, and the traffic information in the traveling direction is mainly transmitted. It is driven by the VICS in-vehicle device optical beacon LED drive circuit.
[0004]
As a conventional VICS vehicle-mounted device optical beacon LED drive circuit of this type, for example, the one described in Patent Document 1 is known and is shown in FIG.
[0005]
In FIG. 6, the VICS in-vehicle device optical beacon LED (hereinafter referred to as LED) drive circuit has LED 1, load resistor 2, and LED drive FET 3 connected in series, and the pulse of the LED emission signal is input to the gate of FET 3. It is the composition to do. Assuming that the forward voltage of LED1 is VFM, a constant voltage VDD is applied to the anode of LED1, the LED driving FET is turned ON while the pulse of the LED light emission signal is Hi, and the current of (VDD−VFM) ÷ RS is applied to LED1. When the pulse of the LED light emission signal is LOW, the LED 1 is turned off, no current flows, and no light is emitted. Thereby, it is comprised so that communication from a VICS vehicle-mounted apparatus to a VICS roadside apparatus may be made.
[0006]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 10-325860
[Problems to be solved by the invention]
However, in such a conventional VICS vehicle-mounted device optical beacon LED drive circuit, it is necessary to pass a large current of about 1 A through the LED 1 for communication from the VICS vehicle-mounted device to the VICS roadside device, and the LED 1 Since the variation in internal resistance is large, the variation in voltage drop due to the internal resistance during light emission of the LED 1 increases, and the forward voltage VFM of the LED 1 varies greatly, for example, varies from about 3.8V to 7.4V.
[0008]
For this reason, the current that flows through the LED 1 varies greatly, the luminous power of the LED 1 varies greatly, and when the forward voltage VFM of the LED 1 is large, the current that flows through the LED 1 is small, and the VICS in-vehicle device to the VICS roadside device Luminous power for communication is insufficient.
[0009]
In addition, when the forward voltage of the LED 1 is low, the current flowing through the LED 1 increases, and the maximum current standard value that can flow through the LED 1 may be exceeded. For this reason, element selection by the forward voltage of LED1 by VFM is required, and since the voltage width is narrow, there is a problem that the yield is deteriorated and the cost of LED1 is increased.
[0010]
The present invention has been made to solve the above-described conventional problems, and can stabilize the LED luminous power and can widen the usable voltage width of the forward voltage VFM of the optical beacon LED. An object of the present invention is to provide an optical beacon LED driving circuit capable of improving the yield and reducing the cost of the LED.
[0011]
[Means for Solving the Problems]
The beacon LED drive circuit of the present invention has a drive circuit that drives the light beacon LED with a constant current in accordance with the pulse of the LED emission signal, and the drive circuit clamps the LED emission signal pulse at a constant voltage amplitude level. An LED light emission signal clamped at a constant voltage is input to the base of the transistor. The clamp circuit has a clamp circuit, a transistor for driving the optical beacon LED, and a resistor interposed between the emitter of the transistor and ground. Thus, the emitter voltage is determined, and the current determined by the resistance between the emitter of the transistor and the ground is caused to flow through the optical beacon LED in accordance with the pulse of the LED light emission signal.
[0012]
With such a configuration, the luminous power of the LED is proportional to the current flowing through the LED, and if the current flowing through the LED is constant, the luminous power can be made constant regardless of the forward voltage VFM of the LED. Therefore, the value of the current flowing through the light beacon LED becomes constant according to the pulse of the LED light emission signal, the light emission power is stabilized, and the LED can be used no matter how small the forward voltage VFM of the LED is. It becomes very wide and the cost of the LED can be reduced.
[0013]
In addition, the current value obtained by dividing the emitter voltage of the transistor that drives the optical beacon LED by the resistance between the emitter and the ground becomes constant as the current value flowing through the optical beacon LED according to the pulse of the LED light emission signal, and the luminous power is stabilized. Even if the LED forward voltage VFM is small, the value of the current flowing through the LED is constant, the element selection range is greatly expanded, and the cost of the LED can be reduced.
[0014]
In the optical beacon LED driving circuit according to the present invention, the clamp circuit is constituted by a Zener diode, and an element having a temperature characteristic of the Zener diode having the same characteristic as that of the base-emitter voltage of the transistor is used. Configured.
[0015]
With such a configuration, the voltage amplitude of the pulse of the light emission signal of the optical beacon LED is fixed to the voltage Vz of the Zener diode, the emitter voltage of the transistor becomes Vz−VBE, the current flowing through the LED becomes constant, and the element selection range is very large In addition to being able to reduce the cost of the LED, and the temperature characteristics of Vz and VBE are matched to each other, even if the temperature changes, the same voltage changes and the emitter voltage remains constant and the current that flows to the LED Remains constant.
[0016]
The optical beacon LED driving circuit according to the present invention is configured such that the clamp circuit includes a diode connected in series with the Zener diode, and the diode corrects the temperature characteristics of the base-emitter voltage of the transistor. The
[0017]
With such a configuration, the voltage amplitude of the pulse of the light emission signal of the optical beacon LED is fixed to the voltage Vz of the Zener diode + the diode voltage VD connected in series, and the emitter voltage of the transistor becomes Vz because VBE = VD, and the current flowing through the LED becomes Since the element selection range is very wide, the LED cost can be reduced, and the temperature characteristics of VD and VBE are the same. Therefore, even if the temperature changes, the emitter voltage Vz remains constant. Yes The current flowing through the LED remains constant.
[0018]
Also, the optical beacon LED driving circuit of the present invention has a voltage dividing circuit between the clamp circuit and the base of the transistor so that the voltage dividing circuit corrects the temperature characteristic of the base-emitter voltage of the transistor. Composed.
[0019]
With this configuration, the voltage amplitude of the pulse of the light beacon LED light emission signal is once fixed to the voltage of the clamp circuit, the voltage is lowered to an arbitrary voltage by the voltage dividing circuit, and the emitter voltage is lowered to the voltage corresponding to VBE from the voltage. The current flowing in the LED is fixed, the element selection range is greatly expanded, and the cost of the LED can be reduced.
[0020]
In addition to this, when the voltage value of the clamp circuit can be freely selected and the temperature characteristics of the VBE of the clamp circuit and the LED driving transistor are different, the temperature can be controlled by giving the voltage divider circuit temperature characteristics. Even if it changes, the emitter voltage remains constant, and the current flowing through the LED remains constant.
[0021]
The optical beacon LED driving circuit according to the present invention includes a clamp circuit that clamps the LED light emission signal pulse to a constant voltage amplitude level, a transistor that drives the LED, and an operational amplifier that controls on / off of the transistor. The clamped LED light emission signal is input to the operational amplifier circuit, the voltage of the load resistance connected between the emitter of the transistor and the ground is fed back to the operational amplifier, and the signal voltage and the load resistance input to the operational amplifier By matching the voltages at, the LED is driven with a constant current in accordance with the pulse of the LED light emission signal.
[0022]
With such a configuration, the value of the current flowing through the light beacon LED becomes constant according to the pulse of the LED light emission signal, the light emission power is stabilized, and the LED can be used regardless of the forward voltage VFM of the LED. As a result, the element selection range is greatly expanded, and the cost of the LED can be reduced.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a first embodiment of an optical beacon LED driving circuit according to the present invention.
[0024]
First, the configuration will be described. In FIG. 1, the drive circuit includes an LEDLED drive element 12 that drives a VICS in-vehicle device optical beacon LED (hereinafter simply referred to as LED) 11, a load resistor 13, and a clamp circuit 14.
[0025]
The LED 11 emits near-infrared light and communicates from the VICS in-vehicle device to the VICS roadside device. The LEDLED driving element 12 is a transistor (for example, an NPN transistor) that drives the LED in accordance with the pulse of the LED light emission signal. The load resistor 13 is a resistor that determines the value of the current flowing through the LED 11. The clamp circuit 14 is a circuit that clamps the pulse of the LED light emission signal to a constant amplitude.
[0026]
Next, the operation of the VICS in-vehicle device optical beacon LED drive circuit configured as described above will be described.
[0027]
First, a pulse of the LED light emission signal enters the clamp circuit 14, is clamped to a constant amplitude voltage, and is input to the base of the transistor of the LED driving element 12. A voltage lower than the base voltage of the transistor by the base-emitter voltage is output as the emitter voltage of the LED driving element 12.
[0028]
A current obtained by dividing the voltage by the load resistance (resistor Rs) 13 flows as the LED drive current of the LED 11, and flows as a constant current during the Hi period of the LED light emission signal pulse regardless of the forward voltage VFM of the LED 11.
[0029]
For this reason, the drive circuit according to the present embodiment does not vary in drive current value as compared with the conventional drive circuit, so that the light emission power (light emission POWER) can be stabilized and is independent of the forward voltage VFM of the LED 11. The current value can be determined. For this reason, the yield of LED11 can be made favorable and element cost can be made cheap.
[0030]
FIG. 2 is a diagram showing a second embodiment of the optical beacon LED driving circuit according to the present invention. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.
[0031]
In FIG. 2, the clamp circuit is composed of a Zener diode 21, which performs the action of clamping the voltage amplitude of the pulse of the input LED light emission signal to the Zener voltage Vz. As the element 21, an element having the same temperature characteristic as the temperature characteristic of the base-emitter voltage of the transistor of the LEDLED driving element 12 is used.
[0032]
Next, the operation of the VICS in-vehicle device optical beacon LED drive circuit configured as described above will be described.
[0033]
First, when a pulse of the LED light emission signal is input, it is clamped to a constant amplitude voltage by the Zener diode 21 and input to the base of the transistor of the LED driving element 12. A voltage lower than the base voltage of the transistor by the base-emitter voltage is output as the emitter voltage of the LED driving element 12.
[0034]
A current obtained by dividing this voltage by the additional resistor (resistor Rs) 13 flows as the LED drive current of the LED 11, and flows as a constant current during the Hi period of the LED light emission signal pulse regardless of the forward voltage VFM of the LED 11.
[0035]
In addition, since the element in which the temperature characteristic of the Zener diode 21 is combined with the temperature characteristic of the base-emitter voltage of the transistor of the LEDLED driving element 12 is used, even if the temperature changes, the emitter voltage of the transistor of the LED driving element 12 is A constant voltage that does not change can be obtained.
[0036]
For this reason, the drive circuit according to the present embodiment does not vary in drive current value as compared with the conventional drive circuit, so that the luminous power can be stabilized, and the current value is independent of the forward voltage VFM of the LED 11. Can be set. For this reason, the yield of LED11 can be made favorable and element cost can be made cheap.
[0037]
FIG. 3 is a diagram showing a third embodiment of the optical beacon LED driving circuit according to the present invention. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.
[0038]
In FIG. 3, the clamp circuit includes a Zener diode 31 and a diode 32. The Zener diode 31 performs the action of clamping the voltage amplitude of the pulse of the input LED light emission signal to the Zener voltage Vz. The diode 32 has a temperature characteristic between the base and emitter of the transistor of the LEDLED driving element 12. An element having the same characteristics as the temperature characteristics of the voltage is used.
[0039]
Next, the operation of the VICS in-vehicle device optical beacon LED drive circuit configured as described above will be described.
[0040]
First, when a pulse of the LED light emission signal is input, it is clamped to a constant amplitude voltage by the diode 32 and the Zener diode 31 and input to the base of the transistor of the LED driving element 12.
[0041]
A voltage lower than the base voltage of the transistor by the base-emitter voltage is output as the emitter voltage of the LED driving element 12. A current obtained by dividing this voltage by the load resistance (resistor Rs) 13 flows as the LED drive current of the LED 11 and flows as a constant current during the Hi period of the pulse of the LED light emission signal regardless of the forward voltage VFM of the LED 11.
[0042]
Further, since the diode 32 uses an element having the same temperature characteristic as the temperature characteristic of the base-emitter voltage of the transistor of the LEDLED driving element 12, even if the temperature changes, the diode 32 has a temperature characteristic. The emitter voltage of the transistor can be a constant voltage that does not change.
[0043]
For this reason, the drive circuit according to the present embodiment does not vary in drive current value as compared with the conventional drive circuit, so that the luminous power can be stabilized, and the current value is independent of the forward voltage VFM of the LED 11. Can be set. For this reason, the yield of LED11 can be made favorable and element cost can be made cheap.
[0044]
Here, the temperature characteristic of the diode 32 is set to be the same as the temperature characteristic of the base-emitter voltage of the transistor of the LEDLED driving element 12. However, when it is desired to intentionally set the inclination due to the temperature, such a temperature correction characteristic is applied. The temperature may be corrected with the diode.
[0045]
FIG. 4 is a diagram showing a fourth embodiment of the optical beacon LED driving circuit according to the present invention. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.
[0046]
In FIG. 4, a Zener diode 41 performs the action of clamping the voltage amplitude of the pulse of the input LED light emission signal to the Zener voltage Vz, and the resistors 42 and 43 voltage-divide the Zener voltage Vz described above, This is a voltage dividing circuit for setting the base voltage of the transistor of the LEDLED driving element 12 to a desired value.
[0047]
Further, an element having the same temperature characteristic of the voltage passing through the voltage dividing circuit as the temperature characteristic of the base-emitter voltage of the transistor of the LEDLED driving element 12 is used.
[0048]
Next, the operation of the VICS in-vehicle device optical beacon LED drive circuit configured as described above will be described.
[0049]
First, when a pulse of the LED light emission signal is input, it is clamped to a constant amplitude voltage by the diode 41, divided to a desired voltage by the resistor 42 and the resistor 43 of the voltage dividing circuit, and applied to the base of the transistor of the LED driving element 12. Entered. A voltage lower than the base voltage of the transistor by the base-emitter voltage is output as the emitter voltage of the LED driving element 12.
[0050]
A current obtained by dividing this voltage by the load resistance (resistor Rs) 13 flows as the LED drive current of the LED 11 and flows as a constant current during the Hi period of the pulse of the LED light emission signal regardless of the forward voltage VFM of the LED 11.
[0051]
The resistors 42 and 43 of the voltage divider circuit use elements whose resistance values change depending on the temperature, and the temperature characteristics of the base voltage of the transistor obtained by dividing the Zener voltage Vz by voltage are the base of the transistor of the LEDLED driving element 12. Since an element having the same characteristic as the temperature characteristic of the voltage between the emitters is used, even if the temperature changes, the emitter voltage of the transistor of the LED driving element 12 can be a constant voltage that does not change.
[0052]
For this reason, the driving circuit according to the present embodiment does not vary in driving current value as compared with the conventional driving circuit, so that the luminous power can be stabilized, and the current is independent of the forward voltage VFM of the LED 11. A value can be set. For this reason, the yield of LED11 can be made favorable and element cost can be made cheap.
[0053]
Here, elements whose resistance values change with temperature are used as the resistors 42 and 43 of the voltage divider circuit, and the temperature characteristics of the base voltage of the transistor obtained by dividing the Zener voltage Vz into voltages are as follows. Although it is assumed that an element with the same characteristics as the temperature characteristics of the base-emitter voltage is used, if you want to intentionally set the slope due to temperature, compensate the temperature using a resistor with the characteristic to apply such temperature correction. It doesn't matter.
[0054]
FIG. 5 is a diagram showing a fifth embodiment of the optical beacon LED driving circuit according to the present invention. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.
[0055]
In FIG. 5, the voltage clamp circuit 51 performs the action of clamping the voltage amplitude of the pulse of the input LED light emission signal to a constant voltage amplitude. The operational amplifier 52 is an element that controls on / off of the transistor of the LEDLED driving element 12, and is a voltage comparison circuit that compares and matches the output voltage of the voltage clamp circuit 51 and the voltage value of the load resistor 13 (resistor Rs).
[0056]
Next, the operation of the VICS in-vehicle device optical beacon LED drive circuit configured as described above will be described.
[0057]
First, when a pulse of the LED light emission signal is input, it is clamped to a constant amplitude voltage by the voltage clamp circuit 51, and the voltage is input to the + input terminal of the operational amplifier 52. The operational amplifier 52 controls the LEDLED driving element 12 so that the voltage of the load resistor 13 connected to the negative input terminal matches the voltage of the positive input terminal.
[0058]
That is, while the LED light emission signal pulse is Hi, the LEDLED driving element 12 is turned on, and a current flows through the LED 11. This current value is controlled so that the load resistance 13 generated by the current flowing in the LED 11 and the voltage value clamped to a constant amplitude voltage by the voltage clamp circuit 51 coincide, and if the + input terminal voltage value is V +, V + / Rs. Thus, the current flows as a constant current during the Hi period of the pulse of the LED light emission signal regardless of the forward voltage VFM of the LED 11.
[0059]
For this reason, the drive circuit according to the present embodiment does not vary in drive current value as compared with the conventional drive circuit, so that the light emission amount can be stabilized, and the current value is independent of the forward voltage VFM of the LED 11. Can be set. For this reason, the yield of LED11 can be made favorable and element cost can be made cheap.
[0060]
In addition, although this Embodiment demonstrated as an optical beacon LED drive circuit used for a VICS system, it can also be used for it if it is not only a VICS system but the communication system by light.
[0061]
【The invention's effect】
According to the present invention, the LED luminous power can be stabilized, the usable voltage width of the forward voltage VFM of the optical beacon LED can be widened, the yield is improved, and the cost of the LED is reduced. It is possible to provide an optical beacon LED driving circuit capable of
[Brief description of the drawings]
FIG. 1 is a block diagram of an optical beacon LED driving circuit according to a first embodiment of the present invention. FIG. 2 is a block diagram of an optical beacon LED driving circuit according to a second embodiment of the present invention. FIG. 4 is a block diagram of an optical beacon LED driving circuit according to a third embodiment. FIG. 4 is a block diagram of an optical beacon LED driving circuit according to a fourth embodiment of the invention. FIG. 5 is an optical beacon LED according to a fifth embodiment of the invention. Block diagram of drive circuit [FIG. 6] Block diagram of conventional VICS vehicle-mounted device optical beacon LED drive circuit [Explanation of symbols]
11 Light beacon LED
12 LED drive element 13 Load resistor 14 Clamp circuit 21, 31, 41 Zener diode 42, 43 Resistance (voltage division circuit)

Claims (5)

An optical beacon LED driving circuit having a driving circuit for driving an optical beacon LED with a constant current in accordance with a pulse of an LED light emission signal,
The drive circuit includes a clamp circuit that clamps the LED light emission signal pulse to a constant voltage amplitude level, a transistor that drives the optical beacon LED, and a resistor that is interposed between an emitter of the transistor and a ground, An LED emission signal clamped at a constant voltage is input to the base of the transistor to determine an emitter voltage, and a current determined by a resistance between the emitter of the transistor and a ground is matched with a pulse of the LED emission signal to generate the light beacon LED. An optical beacon LED driving circuit, 2. The optical beacon LED driving circuit according to claim 1, wherein the clamp circuit is constituted by a Zener diode, and an element having a temperature characteristic of the Zener diode that is the same as a temperature characteristic of the base-emitter voltage is used. . 3. The optical beacon LED driving circuit according to claim 2, wherein the clamp circuit is constituted by a diode connected in series with the Zener diode, and the temperature characteristic of the base-emitter voltage of the transistor is corrected by the diode. 2. The optical beacon LED drive according to claim 1, further comprising a voltage dividing circuit between the clamp circuit and a base of the transistor, wherein the voltage dividing circuit corrects a temperature characteristic of a base-emitter voltage of the transistor. circuit. The drive circuit includes a clamp circuit that clamps the LED light emission signal pulse to a constant voltage amplitude level, a transistor that drives the LED, and an operational amplifier circuit that controls on / off of the transistor, and the clamped LED light emission signal Is input to the operational amplifier circuit, the voltage of the load resistor connected between the emitter of the transistor and the ground is fed back to the operational amplifier, and the signal voltage input to the operational amplifier is matched with the voltage at the load resistor, so that the LED light emission signal The optical beacon LED driving circuit according to claim 1, wherein the LED is driven with a constant current in accordance with the pulse.

Images