JPH0969769A - Semiconductor light emission driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a semiconductor light emitting device and a switching element from the surge voltage generated from an inductive load or the like by connecting a first rectification element in antiparallel with the semiconductor light emitting device and connecting a second rectification element between main terminals of the switching element in the reverse direction. SOLUTION: A series circuit of a semiconductor light emitting device 3 and a switching element (transistor TR) 4 which has one main terminal 4c connected to the semiconductor light emitting device 3 is provided, and a DC power source is connected to this series circuit. A first rectification element (diode) 12 is connected in the reverse direction of and in parallel with the semiconductor light emitting device 3, and a second rectification element (diode) 13 is connected between main terminals 4c and 4e of the TR 4 in the reverse direction of the TR 4. If the GND terminal goes to a high potential by generation of a surge voltage caused by disconnection of various inductive loads in this constitution, a high voltage is prevented from being applied to the TR 4 and the semiconductor light emitting device 3 because the surge current flows through diodes 13 and 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting drive circuit, and more particularly to a semiconductor light emitting drive circuit for transmitting an optical signal such as infrared rays.

[0002]

2. Description of the Related Art In order to detect the traffic volume of a vehicle on a road, an infrared signal is transmitted from a semiconductor light emitting drive circuit mounted on the vehicle, and this signal is received by a vehicle detector installed on a pillar beside the road. Means are being developed as part of building a traffic control system. A conventional example of this type of semiconductor light emitting drive circuit is shown in FIG. The semiconductor light emitting drive circuit includes a semiconductor light emitting device 3 including a plurality of infrared light emitting diodes 1 and a plurality of resistors 2, and first and second transistors 4 and 5 as first and second switching elements,
A capacitor 6 and an electrolytic capacitor 7 are connected between the V _CC terminal and the GND terminal of a DC power supply (not shown). First
The collector of the transistor 4 is connected to one end of the semiconductor light emitting device, and the base of the first transistor 4 is connected to the collector of the second transistor 5 via the resistor 11.
The emitters of the first and second transistors 4 and 5 are connected to the GND terminal, respectively. The base of the second transistor 5 is connected to the control input terminal IN via the resistor 10. The resistor 8 is connected between the V _CC terminal and the resistor 11, and the resistor 9 is connected between the V _CC terminal and the resistor 10.

FIG. 4 shows operation waveforms of the semiconductor light emitting drive circuit of FIG. The control input terminal I is used to send a signal to the vehicle detector to inform the vehicle detector that the vehicle has passed.
The control signal V _IN is applied to N. When the control signal V _{IN applied} to the control input terminal IN is at a high level (H level), a base current flows from the DC power supply terminal V _CC to the second transistor 5 through the resistors 9 and 10, and the second transistor 5 Is turned on. Therefore, the base potential of the first transistor 4 decreases, the first transistor 4 is turned off, the power is not supplied from the DC power supply terminal V _CC to the semiconductor light emitting device 3, and the plurality of infrared light emitting diodes 1 emit light. do not do.

On the other hand, when the signal V _{IN applied} to the control input terminal IN is at a low level (L level), the base current of the second transistor 5 decreases and the second transistor 5 is turned off. Therefore, the base current flows through the first transistor 4, and the first transistor 4 is turned on. As a result, from the DC power supply terminal V _CC to the semiconductor light emitting device 3
Is supplied with electric current to flow a current I _D , the plurality of infrared light emitting diodes 1 emit light, and a signal indicating passage of the vehicle or the like is sent to the vehicle detector.

[0005]

By the way, in the drive circuit of FIG. 3, the semiconductor light emitting device 3 and the first switching element are connected by the various inductive loads such as relays and solenoids connected to the vehicle battery. Transistor 4 may be adversely affected. That is, when a surge voltage generated from an inductive load or the like causes the GND terminal to have a high potential and the reverse high voltage is applied to the infrared light emitting diode 1 and the first transistor 4, these elements may be destroyed. is there. Therefore, it is an object of the present invention to provide a semiconductor light emitting drive circuit that protects a semiconductor light emitting device and a switching element from a surge voltage generated by various inductive loads connected to a battery.

[0006]

A semiconductor light emitting drive circuit according to the present invention comprises a semiconductor light emitting device and a series circuit of a switching element having one main terminal connected to the semiconductor light emitting device, the series circuit being a DC power source. Connected to. The first rectifying element is connected in parallel with the semiconductor light emitting device, and the second rectifying element is connected between the main terminals of the switching element. Also,
In another semiconductor light emitting drive circuit according to the present invention, the switching element is a MOS field effect transistor, and a rectifying element is connected in parallel with the semiconductor light emitting device.

According to the present invention, even if a reverse high voltage is applied to the semiconductor light emitting device and the switching element due to the surge voltage generated from the inductive load or the like, the first rectifying element (in parallel with the semiconductor light emitting device) ( In the invention according to claim 2, a rectifying element) and a second rectifying element connected between the main terminals of the switching element (in the invention according to claim 2, a diode formed between the drain and source of the MOS field effect transistor). The semiconductor light emitting device and the switching element can be protected from the surge voltage because they are short-circuited.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a semiconductor light emitting drive circuit according to the present invention will be described below with reference to FIG. In FIG. 1, the same parts as those shown in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted. The semiconductor light emitting drive circuit shown in FIG. 1 includes a semiconductor light emitting device 3 including a plurality of infrared light emitting diodes 1 and a plurality of resistors 2, and the semiconductor light emitting device 3
A first transistor 4 as a first switching element having a collector 4c, which is one of the main terminals, connected to
Further, a first diode 12 is provided as a first rectifying element connected in parallel with the semiconductor light emitting device 3 in the opposite direction, and a second rectifying element is provided between the collector 4c and the emitter 4e of the first transistor 4. Second diode 13 of is connected in the opposite direction to the first transistor 4.

The normal operation of the semiconductor light emitting drive circuit shown in FIG. 1 is the same as that of the semiconductor light emitting drive circuit shown in FIG. 3, but a surge voltage is generated due to disconnection of various inductive loads and GN is generated.
When the D terminal becomes high potential, the first transistor 4
And a second diode 13 connected in anti-parallel with the first diode 12 connected in anti-parallel with the semiconductor light emitting device 3.
Since a surge current flows through the and, a high voltage is prevented from being applied to the first transistor 4 and the semiconductor light emitting device 3. Therefore, it is extremely unlikely that these elements will be destroyed by the application of high voltage. Further, since the first diode 12 and the second diode 13 are connected in series, it is possible to use a diode having a small breakdown voltage.

The present invention is not limited to the above-mentioned embodiment, but can be modified. For example, the resistor 9 may be omitted, and the control signal may be directly supplied from the control input terminal IN to the base of the second transistor 5.

[0011]

EXAMPLE The first transistor 4 was a bipolar transistor in the embodiment shown in FIG.
Alternatively, the MOS field effect transistor 15 can be used as the first transistor as shown in FIG. In this case, the collector of the second transistor 25
A constant voltage diode 14 is provided between the emitters to prevent electrostatic breakdown of the gate of the MOS field effect transistor 15.
Is connected. Also, a MOS field effect transistor 1
5 has a diode replacing the diode 13
Since it is formed between the sources, it is not necessary to separately connect the second diode 13 as in FIG.

Also in the semiconductor light emitting drive circuit shown in FIG. 2, the control signal V _IN shown in FIG. 4 is applied to the control input terminal IN in order to send a signal indicating the passage of the vehicle to the vehicle detector. When the signal V _{IN applied} to the control input terminal IN is at a high level (H level), the base current of the second transistor 5 flows from the DC power supply terminal V _CC through the resistors 9 and 10, and the second transistor 5 is Turns on. Therefore, the gate potential of the MOS field effect transistor 15 is lowered, the MOS field effect transistor 15 is turned off, the power is not supplied from the DC power supply terminal V _CC to the semiconductor light emitting device 3, and the plurality of infrared light emitting diodes 1 are Does not emit light.

On the other hand, when the signal V _{IN applied} to the control input terminal IN is at a low level (L level), the base current of the second transistor 5 decreases and the second transistor 5 is turned off. Therefore, the gate potential of the MOS field effect transistor 15 rises and the MOS field effect transistor 15 is turned on. As a result, power is supplied to the semiconductor light emitting device 3 from the DC power supply terminal V _CC, and the current I
_D flows, the plurality of infrared light emitting diodes 1 emit light, and a signal indicating the passage of the vehicle is sent to the vehicle detector.

[0014]

According to the present invention, the semiconductor light emitting device and the switching element of the semiconductor light emitting drive circuit can be protected from the surge voltage generated by various inductive loads connected to the battery.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing an embodiment of a semiconductor light emitting drive circuit according to the present invention.

FIG. 2 is an electric circuit diagram showing an embodiment of the present invention.

FIG. 3 is an electric circuit diagram showing a conventional example of a semiconductor light emitting drive circuit.

FIG. 4 is a waveform diagram showing the relationship between the control terminal voltage of the circuit of FIG. 3 and the current flowing through the semiconductor light emitting device.

[Explanation of symbols]

3. . 3. Semiconductor light emitting device, . First transistor (switching element), 4c. . Collector (one main terminal), 4e. . Emitter (main terminal), 12. . First
Rectifying element of 13. . Second rectifying element, 15. . M
OS type field effect transistor (switching element)

Claims (2)

[Claims] 1. A semiconductor light-emitting drive circuit comprising a semiconductor light-emitting device and a switching element in which one main terminal is connected to the semiconductor light-emitting device, the series circuit being connected to a DC power supply. An element connected in parallel with the semiconductor light emitting device,
A semiconductor light emitting drive circuit characterized in that a second rectifying element is connected between main terminals of the switching element. 2. A semiconductor light emitting drive circuit, comprising a semiconductor light emitting device and a switching element having one main terminal connected to the semiconductor light emitting device, wherein the series circuit is connected to a DC power source, wherein the switching element is A semiconductor light emitting drive circuit comprising a MOS field effect transistor, wherein a rectifying element is connected in parallel with the semiconductor light emitting device.