JP2004014183A - Illumination voltage switching circuit for electric display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an illumination voltage switching circuit for an electric display device of mainly an onboard audio apparatus. <P>SOLUTION: The switching circuit comprises a PNP transistor Q1 where the input voltage VIN is applied to the emitter and the collector voltage is an output voltage VOUT, an emitter-grounded NPN transistor Q2 where the collector is connected to the base of the PNP transistor Q1 and a first external control voltage VON/OFF is applied to the base through a resistor R1, an NPN transistor Q3 where the collector is connected to the base of the NPN transistor Q2 to control the on/off of the NPN transistor Q2, a zener diode D1 which is inserted between the output voltage VOUT and the base of the NPN transistor Q3, and an emitter-grounded NPN transistor Q4 where the collector is connected to the emitter of the NPN transistor Q3 and a second external control voltage V' ON/OFF is applied to the base. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an illumination voltage switching circuit of an electronic display device of an in-vehicle audio device.
[0002]
[Prior art]
Lighting of audio equipment, especially light-emitting diodes, liquid crystal, and other light-emitting display devices of in-vehicle audio equipment is not limited to simple on / off switching of illumination, but is generally adapted to reduce illumination at night. However, the three-stage lighting voltage switching circuit of lighting ON / dimming / OFF is complicated and heavy by using a transformer or the like, and is not inexpensive.
[0003]
Meanwhile, as a general-purpose constant voltage circuit, there is a feedback constant voltage circuit 10 having a configuration in which an output voltage VOUT is controlled to a certain voltage by an external control voltage VON / OFF with respect to an input voltage VIN as shown in FIG. . This circuit has a simple configuration in which a constant voltage circuit operates by applying a certain stabilized external control voltage VON / OFF to the resistor R1, and is realized at low cost.
[0004]
At this time, the NPN transistor Q3 in FIG. 2 controls the ON / OFF of the NPN transistor Q2 at the boundary of (voltage of the Zener diode D1) + (ON voltage of the NPN transistor Q3) and VOUT (collector output of the PNP transistor Q1). Is approximately fixed to the value of (the voltage of the Zener diode D1) + (the ON voltage of the NPN transistor Q3). The capacitors C1 and C2 in FIG. 2 are operation stabilizing capacitors inserted for stabilizing the circuit operation.
[0005]
[Problems to be solved by the invention]
According to the present invention, an illumination voltage switching circuit capable of switching between three levels of ON / dimming / OFF of the light-emitting display device of the audio equipment is provided by using the feedback type constant voltage circuit and a second external control voltage V '. By adding one NPN transistor Q4 which is turned on / off by ON / OFF, not only the ON / OFF of the constant voltage circuit but also the through voltage of the input voltage VIN which is not constant voltage is output. A constant voltage circuit capable of outputting a three-stage voltage corresponding to / dimming / off is provided as an illumination voltage switching circuit of an electro-optical display device.
[0006]
[Means for Solving the Problems]
The present invention relates to a feedback type constant voltage circuit using a Zener diode and a transistor used in an electro-optical display device, wherein a PNP transistor Q1 having an input voltage VIN applied to an emitter side and having a collector voltage as an output voltage VOUT; A collector is connected to the base side of the PNP transistor Q1, and a first external control voltage VON / OFF is applied to the base via a resistor R1. The grounded NPN transistor Q2 is connected to the base side of the NPN transistor Q2. An NPN transistor Q3 connected to a collector to perform on / off control of the NPN transistor Q2; a Zener diode D1 inserted between the output voltage VOUT and the base side of the NPN transistor Q3; and an emitter of the NPN transistor Q3. Collector on the side And a grounded emitter NPN transistor Q4 to which a second external control voltage V'ON / OFF is applied to the base side, thereby providing an illumination voltage switching circuit 20 for an electro-optical display device. To achieve the above object.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of an illumination voltage switching circuit of an electro-optical display device according to the present invention will be described with reference to the drawings.
[0008]
FIG. 1 is a circuit diagram of an illumination voltage switching circuit of the electro-optical display device according to the present invention.
[0009]
First, in the example of the embodiment of the present invention, it is premised that the first stabilized first external control voltage VON / OFF using the Zener diode D1 and the transistors Q1, Q2, and Q3 shown in FIG. It is based on a feedback constant voltage circuit 10 as a voltage switching circuit that works by applying an external control voltage voltage VON. The feedback type constant voltage circuit 10 of FIG. 2 is based on the output voltage VOUT of 0 V or (the voltage of the Zener diode D1) + (the ON voltage of the NPN transistor Q3) according to the first external control voltage VON / OFF. Fixed to a value.
[0010]
The illumination voltage switching circuit 20 according to the present invention includes, in addition to the configuration of the feedback type constant voltage circuit 10, a grounded emitter NPN transistor Q4 to which a second external control voltage V'ON / OFF is applied to a base. Are connected in series to the emitter side.
[0011]
More specifically, a PNP transistor Q1 whose input voltage VIN is applied to the emitter side and whose collector voltage is an output voltage VOUT, a collector is connected to the base side of the PNP transistor Q1, and a first external control is connected to the base. A grounded NPN transistor Q2 to which the voltage VON / OFF is applied via a resistor R1, an NPN transistor Q3 having a collector connected to the base side of the NPN transistor Q2 and performing on / off control of the NPN transistor Q2; A Zener diode D1 inserted between the output voltage VOUT and the base side of the NPN transistor Q3; a collector connected to the emitter side of the NPN transistor Q3 and a second external control voltage V'ON / OFF is applied to the grounded emitter. And PN transistors Q4, a circuit configuration comprising a. Note that a backflow prevention diode D2 is inserted to prevent backflow from the NPN transistor Q3 when the NPN transistor Q4 is off.
[0012]
In the ON state where a voltage is applied to the second external control voltage V'ON / OFF on the base side of the NPN transistor Q4 to turn on the NPN transistor Q4, the first external control voltage VON is applied to the resistor R1. When the / OFF voltage is applied, the voltage switching circuit starts operating similarly to the feedback constant voltage circuit 10.
[0013]
Next, when the NPN transistor Q4 is turned off (0 V) without applying a voltage, the NPN transistor Q4 is turned off, and the NPN transistor Q3 connected thereto is also turned off. Therefore, the voltage control NPN transistor Q2 is completely turned on, and the voltage of VIN is directly output to VOUT as a through voltage.
[0014]
The above circuit can control not only on / off of lighting but also three kinds of voltage levels such as a case of lighting at night and dimming light.
[0015]
That is, by turning off the second external control voltage V'ON / OFF (0 V) and turning on the first external control voltage VON / OFF to a constant voltage, the NPN transistor Q2 is completely turned on. And the second external control voltage V'ON / OFF is turned on and the first external control voltage V'ON / OFF is turned on. By turning on the external control voltage VON / OFF to a constant voltage, the constant voltage circuit is operated to make the output voltage VOUT approximately stable to the above (zener voltage Vz) + (the ON voltage of the NPN transistor Q3). (Dimming illumination), three stages of illumination off state in which the first external control voltage VON / OFF is turned off to make the output voltage VOUT 0 V Lighting voltage is of the switching circuit of the electronic display device.
[0016]
【The invention's effect】
Since the illumination voltage switching circuit of the electro-optical display device according to the present invention is configured as described above, the illumination voltage switching circuit is a simple and low-cost constant voltage circuit with a small number of elements. There is an excellent effect that the illumination voltage switching in the three states of light illumination and illumination off is realized by control using the first external control voltage VON / OFF and the second external control voltage V'ON / OFF.
[Brief description of the drawings]
FIG. 1 is an illumination voltage switching circuit diagram of an electro-optical display device according to the present invention.
FIG. 2 is a circuit diagram example of a conventional feedback type constant voltage circuit.
[Explanation of symbols]
Q1 PNP transistor Q2 NPN transistor Q3 NPN transistor Q4 NPN transistor R1 Resistance C1, C2 Operation stabilizing capacitor D1 Zener diode D2 Reverse current prevention diode VIN Input voltage VOUT Output voltage VON / OFF First external control voltage V'ON / OFF 2 external control voltage 10 feedback type constant voltage circuit 20 lighting voltage switching circuit

Claims (1)

A feedback type constant voltage circuit using a Zener diode and a transistor used in an electro-optical display device,
An input voltage VIN is applied to the emitter side and a PNP transistor Q1 having a collector voltage as an output voltage VOUT. A collector is connected to the base side of the PNP transistor Q1 and a first external control voltage VON / OFF is connected to the base. A grounded NPN transistor Q2 applied through a resistor R1, an NPN transistor Q3 having a collector connected to the base of the NPN transistor Q2 to perform on / off control of the NPN transistor Q2, and an output voltage VOUT. A Zener diode D1 inserted between the base side of the NPN transistor Q3, a collector connected to the emitter side of the NPN transistor Q3, and a second external control voltage V'ON / OFF applied to the base side. NPN transistor with common emitter Lighting voltage switching circuit of electronic display device, characterized in that it comprises a data Q4, the.

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