JPH01320822A - Projector for photoelectric switch - Google Patents

Abstract

PURPOSE:To evade delay in start or delay of a projector by connecting a collector/emitter of a voltage detection transistor(Tr) between a base and emitter of an output Tr and applying a power voltage to a base of the voltage detection Tr. CONSTITUTION:The collector and emitter of the voltage detection Tr 15 are connected between the base and emitter of the output Tr 10 and the voltage of the power supply 1 is applied to the base. When the switch 2 is closed, the Tr 15 is turned on, the Tr 10 is turned off and no light emitting diode 8 is operated. When the switch 2 is opened and the power supply 1 is interrupted, the Tr 15 is turned off. Thus, since the Tr 10 is turned on/off by a pulse train from a pulse generating circuit 7, a light emitting diode 8 is lighted. Since the power interruption 1 is short in time, the power is supplied from a smoothing capacitor 5. In the case of selecting the static capacitance of the capacitor 5 largely, the voltage change is decreased and the projecting time is extended.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a light projector for a photoelectric switch that detects the presence or absence of a target object based on the amount of pulsed light emitted from a light emitting element reaching a light receiving element. .

[Conventional technology]

2. Description of the Related Art Conventionally, as a light projecting device for a photoelectric switch of this kind, one shown in FIG. 2 is known. In FIG. 2, the light projecting device for the photoelectric switch is driven by the power supply 1 applied by closing the switch 2. Smoothing capacitor 5 is charged with the power supply voltage via resistor 3 and diode 4, and the voltage charged in capacitor 5 is stabilized. (Although the power supply l is shown as a battery in the figure, it is often a rectified power supply.) The output terminal of the voltage regulator 6 is connected to the pulse generation circuit 7, the light emitting diode 8, the resistor 9, and the collector/emitter of the output transistor 10. connected to the series circuit. The output terminal of the pulse generating circuit 7 is connected to the base of the transistor 10. In the light receiving device, a photodiode 11 for a light emitting diode 8 is connected to a detection circuit 12, and is driven by a power source 13. 14 is the detection circuit 12, that is, the output end of the light receiving device.

When the switch 2 is closed, the voltage is smoothed by a smoothing circuit formed by a resistor 3, a diode 4, and a capacitor 5, and then applied to a constant voltage device 6. 4 is a diode for preventing reverse current when the power supply voltage decreases. Pulse generation circuit 7
When the power supply voltage is applied, a predetermined pulse train is generated, the transistor 1° is turned on and off, and a pulse current is passed through the light emitting diode 8, so that the light emitting diode 8 emits pulse light. The photodiode 11 receives the pulsed light from the light emitting diode 1o, and generates an output at the output terminal 14 via the detection circuit 12.

[Problem to be solved by the invention]

In the photoelectric switch as described above, there are cases where it is desired to operate the light projecting device only for a predetermined short time when the switch 2 is opened. For example, when trying to detect a momentary power outage, in a conventional photoelectric switch, switch 2 is opened (power off), and the power is cut off when the photodiode 11 of the light receiving device no longer receives light from the light emitting diode 8. You can know.

However, even if the switch 2 is opened when stopping the projector, the pulse generation circuit 7 continues to operate until the charging voltage of the capacitor 5 drops sufficiently and the voltage regulator 6 stops operating.
Since the light emitting diode 8 continues to emit light, it is impossible to stop the light projecting device as quickly as possible. In other words, there is a problem in that there is a delay in the stop time of the light projector. Note that if the smoothing capacitor is made smaller, the projector will start and stop a little faster (
However, there was a problem in that it became difficult to smooth the power supply.

SUMMARY OF THE INVENTION An object of the present invention is to provide a light emitting device for a photoelectric switch that minimizes the charging and discharging current of a smoothing capacitor, reduces power pulsation as much as possible, and eliminates delays in starting or stopping the light projecting device. .

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention includes a smoothing capacitor that smoothes the power supply voltage, a voltage regulator that stabilizes the voltage across the smoothing capacitor, and a voltage regulator that is connected to the output end of the voltage regulator and generates a pulse train. For a photoelectric switch, a pulse generation circuit that generates a pulse, a series circuit of a light emitting element and a collector/emitter of an output transistor is connected in parallel with the pulse generation circuit, and the base of the output transistor is connected to the output end of the pulse generation circuit. In the light projecting device, the collector and emitter of a voltage detection transistor are connected between the base and emitter of the output transistor, and the voltage detection transistor is connected to the base so that the power supply voltage is applied to the base of the voltage detection transistor.

[For production]

In the present invention, power supply voltage is always applied to the light emitting device, but the output transistor is turned off by a voltage detection transistor to prevent pulse current from flowing to the light emitting element. During the short period when the transistor is turned on and the power is cut off, the energy charged in the smoothing capacitor emits pulses through the constant voltage device and pulse generation circuit, and the light emitter emits light during the charging and discharging time of the smoothing capacitor. Starts and stops without being affected.

〔Example〕

A first embodiment of a light projecting device for a photoelectric switch according to the present invention will be described below.
Components that are the same as those in FIG. 2 are given the same reference numerals as in FIG. 2. In FIG. 1, a power supply 1, a switch 2. The constant voltage device 6, pulse generation circuit 7, etc. of the smoothing capacitor 5 are the same as those of the conventional ones, so their explanation will be omitted. The difference between this projector and conventional ones is that the output transistor 1
The collector and emitter of the voltage detection transistor 15 are connected between the base and emitter of the voltage detection transistor 15, and the voltage of the power supply 1 is applied to the base thereof. In order to do this, a resistor 16 is connected in parallel with the series circuit of the power supply 1 and the switch 2, and is connected so that the voltage across the resistor 16 is applied to the base of the transistor 15 via the resistor 17.

With the above configuration, when the switch 2 is closed, the capacitor 5 is charged and power is supplied to the pulse circuit 7 via the voltage regulator 6, and the pulse generating circuit 7 generates a pulse train.
The voltage of the power supply 1 is applied to the base of the transistor 15 via the resistor 17, turning on the transistor 15 and bypassing the base current of the transistor 10, turning off the transistor 10. Since the light emitting diode 8 is not energized, the light emitting device is turned off. doesn't work. When switch 2 is opened and power supply 1 is cut off, the base of transistor 15 is connected to both resistors 16.1
7, the transistor 15 is turned off because the potential is the same as that of its emitter and no base current flows. Therefore, a pulse train is applied from the pulse generation circuit 7 to the base of the transistor 10, and the transistor 10 is turned on and off by this pulse train, and a pulse current flows through the light emitting diode 8 due to the on and off of the transistor 10, so that the light emitting diode 8
emits light, and the light projector emits light. Since the power supply 1 is shut off for a short time, power is supplied from the capacitor 5 during this time. Therefore, if the capacitance of the capacitor 5 is selected to be sufficiently large, the voltage change due to discharge of the capacitor 5 can be reduced, and the light projection time can be increased to a certain extent.

〔Effect of the invention〕

According to the present invention, the interruption of the power supply is detected by the voltage detection transistor, and the light projection device is activated when the power supply is interrupted, so that it is possible to start and stop with a quick response.

In addition, since the operating time of the projector is short, there is no need to completely discharge the smoothing capacitor, and the charging current may be small.
The effect of reducing voltage fluctuation can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a wiring diagram showing an embodiment of a light projecting device for a photoelectric switch according to the present invention, and FIG. 2 is a wiring diagram showing an example of a conventional light projecting device for a photoelectric switch.

Claims (1)

[Claims] 1) A smoothing capacitor that smoothes the power supply voltage, a voltage regulator that stabilizes the voltage across the smoothing capacitor, a pulse generation circuit that is connected to the output terminal of the voltage regulator that generates a pulse train, and a light emitting element. In a light projector for a photoelectric switch, a series circuit of a collector and an emitter of an output transistor is connected in parallel with the pulse generation circuit, and a base of the output transistor is connected to an output end of the pulse generation circuit. - A light projection device for a photoelectric switch, characterized in that the collector and emitter of a voltage detection transistor are connected between the emitters, and the power supply voltage is applied to the base of the voltage detection transistor.