JP2609924B2 - Optical sensor circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sensor circuit used in a position detecting device that has a light emitting unit and a light receiving unit and detects a position by blocking the emitted light. It is.

<Prior Art> Conventional optical sensor circuits are generally the same as those described in Sharp Data Book Optical Semiconductor Edition (September 1986, 2nd edition, published by Seibundo Shinkosha).
Something is described on page 685.

In this conventional example, as shown in FIG. 5 (a), a light emitting diode 1, a phototransistor 2, and an NPN transistor 3 are connected in parallel to a power supply Vcc via resistors 4, 7, 5 respectively, and the emitter of the phototransistor 2 is connected to a power supply Vcc. The light-shielding plate 6 is connected to the base of the NPN transistor 3 and is provided between the light emitting diode 1 and the phototransistor 2 so as to be able to enter and exit.

As for the operation, the light emitting diode 1 emits light with a constant current flowing through the resistor 4, and the phototransistor 2 receives the light emitted from the light emitting diode 1, and the current flows to turn on the NPN transistor 3. When the light emitted from the light emitting diode 1 is shielded by the light shielding plate 6, no current flows through the phototransistor 2, so that the NPN transistor 3 is turned off.

The waveform diagram of FIG. 5 (b) shows the above situation, and the output signal power V _OUT becomes the collector-emitter voltage V _CE of the NPN transistor 3 when “bright” and Vcc when “dark”.

<Problems to be Solved by the Invention> In the above-described conventional example, circuit components are used because the voltage between the base and the emitter of the NPN transistor 3 is used to make the voltage between the collector and the emitter of the phototransistor 2 substantially constant. Needed a lot.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the related art, and has as its object to provide an optical sensor circuit with a small number of circuit components and good responsiveness, and to provide an optical sensor circuit that obtains a relatively large signal as an output signal. I do.

<Means for Solving the Problems> In order to achieve the above object, according to the present invention, a series circuit of an impedance element and a light emitting diode supplied from a power supply unit, and an anode of the light emitting diode are formed on a base. A series circuit of a connected NPN transistor and a light receiving element connected between the emitter of the transistor and the ground is connected between the power supply unit and the ground to take out a signal from the collector of the transistor. The present invention relates to a series circuit of a light emitting diode and an impedance element fed from a power supply unit, a series circuit of a PNP transistor whose cathode is connected to a base, and a light receiving element connected between the emitter of the transistor and the power supply unit. Is connected between the power supply unit and the ground, and a signal is taken out from the collector of the transistor.

<Operation> In the optical sensor circuit having the above-described configuration, the terminal voltage of the light receiving element becomes constant and the constant current operation becomes possible, so that the response speed of the light receiving element is improved and a relatively large signal value is output as a signal. be able to.

<Example> Hereinafter, a first example of the present invention will be described with reference to FIG.

In FIG. 1A, a light emitting diode 11 as a light emitting element is connected between a power supply Vcc and GND through a resistor 14 as an impedance element, and an NPN transistor 1 is connected.
A phototransistor 12 serving as a light receiving element connected to the emitter terminal of the light-emitting diode 3 is connected through a resistor 15, a base terminal of an NPN transistor 13 is connected to an anode terminal of the light-emitting diode 11, and a collector terminal of the NPN transistor 13 is output. The light shielding plate 16 is disposed between the light emitting diode 11 and the phototransistor 12 so as to be able to enter and exit. Here, the base current flowing when the NPN transistor 13 is turned on is negligible compared to the current flowing through the light emitting diode 11.

Regarding the operation of the present embodiment having the above configuration, when light emitted from the light emitting diode 11 is received by the phototransistor 12,
A current flows through the phototransistor 12. As a result, NPN
The transistor 13 is turned on by performing a base ground operation. The collector voltage of the NPN transistor 13 is V _F −V _BE + V
Become _CE . Here, V _F is the anode voltage of the light emitting diode 11, V _BE is the base-emitter voltage of the NPN transistor 13, and V _CE is the collector-emitter voltage of the NPN transistor 13 when it is on. Therefore, V _F = 1.2 V, V _BE = 0.7 V, V _CE =
If it is 0.2V, the collector voltage will be 0.7V.

Next, when the light emitted from the light emitting diode 11 is shielded by the light shielding plate 16, no current flows through the phototransistor 12, so that the NPN transistor 13 is turned off. As a result, the collector voltage of NPN transistor 13 becomes Vcc. Fig. 1 (b)
This waveform diagram shows this situation.

Further, the light emitting forward voltage V _F of the diode 11 exhibits a negative temperature characteristic, but the base of the NPN transistor 13 - to indicate the emitter voltage negative temperature characteristic, the phototransistor
The 12 collector voltages are less affected by temperature.

FIG. 2 shows a second embodiment of the present invention. For the sake of simplicity, the same parts as those of the embodiment shown in FIG.

In this embodiment, a PNP transistor 13 'is used in place of the NPN transistor 13 of the first embodiment, the light emitting diode 11 and the phototransistor 12 are connected to the power supply Vcc side, and the resistors 14 and 15 are connected to the GND side, respectively. The light emitting diode 11 has a cathode connected to the base of a PNP transistor 13 '. Other configurations are the same as those of the first embodiment.

In this embodiment having the above configuration, as shown in the waveform diagram of FIG. 2 (b), the output signal voltage Vout at the time of light and dark is inverted from that of the first embodiment, and the output at the time of light is output. The signal voltage V _OUT is Vc
c−V _F + V _BE −V _CE and the output signal voltage V _{OUT in} darkness is 0V
Becomes

FIGS. 3 and 4 show a third and a fourth embodiment of the present invention, respectively.

In the third and fourth embodiments, a photodiode 12 'is used in place of the phototransistor 12 in the embodiments of FIGS. 1 and 2, respectively.

The operation of the third and fourth embodiments having the above configuration is the same as the operation of the embodiment of FIGS. 1 and 2, respectively.

<Effects of the Invention> According to the present invention, as described above, by using the terminal voltage of the light emitting element as the reference voltage, the circuit configuration can be simplified, the temperature characteristics can be corrected, and a large signal as a signal can be obtained. There is an effect that a value output can be obtained.

[Brief description of the drawings]

1A and 1B show a first embodiment of the present invention, in which FIG. 1A shows an optical sensor circuit thereof, FIG. 1B shows an operation waveform diagram thereof, and FIG. 2 shows a second embodiment of the present invention, wherein FIG. FIG. 3B is a circuit diagram thereof, FIG. 3B is an operation waveform diagram thereof, FIG. 3 is a circuit diagram of a third embodiment of the present invention, FIG. 4 is a circuit diagram of a fourth embodiment of the present invention, and FIG. (A) is a circuit diagram of the conventional optical sensor circuit, (b)
FIG. 4 is an operation waveform diagram thereof. 11: Light-emitting diode (light-emitting element), 12: Phototransistor (light-receiving element), 12 ': Photodiode, 13
…… NPN transistor, 13 '…… PNP transistor, 14,1
5 ... resistor, 16 ... shield plate.

Claims (2)

(57) [Claims] 1. A series circuit of an impedance element and a light emitting diode fed from a power supply unit, a series of an NPN transistor having an anode connected to the base of the light emitting diode, and a light receiving element connected between the emitter of the transistor and ground. An optical sensor circuit wherein a circuit is connected between a power supply unit and a ground, and a signal is extracted from a collector of the transistor. 2. A series circuit of a light emitting diode and an impedance element fed from a power supply unit, a PNP transistor having a cathode connected to the base of the light emitting diode, and a light receiving element connected between the emitter of the transistor and the power supply unit. An optical sensor circuit wherein a series circuit is connected between a power supply unit and a ground, and a signal is extracted from a collector of the transistor.