JPH04168808A - Photoelectric switch - Google Patents

Abstract

PURPOSE:To reduce the power consumption without causing a decrease in detection sensitivity nor the complexity of a circuit by causing the voltage of a power line to drop by using a step-down type switching regulator which is placed in switching operation with a light projection signal to supply electric power to a light projection circuit. CONSTITUTION:When a transistor(TR) 7 turns on in the step-down type switching regulator 3, a current flows in the light projection circuit 4 from the power line through a reactor 8. When the TR 7 turns off, a flywheel diode 9 turns on with the counter electromotive force generated at the reactor 8. The current which flows to the reactor 8, therefore, continues to flow as the charging current to a smoothing capacitor 10. Consequently, the output voltage Vout developed across the smoothing capacitor 10 of the regulator 3 is nearly a half as high as the input voltage Vin and the output mean current Iout is about twice as large as the input mean current Iin flowing in from the power line. The inflow current from the power line can be suppressed to almost a half as large as usual.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a photoelectric switch that reduces current consumption.

(Prior art) A photoelectric switch is a light emitting circuit for lighting a light emitting element such as an LED in pulses, amplifying and synchronously detecting a received light signal from a light receiving element, and detecting the received light signal when the level of the received light signal exceeds a predetermined value. The light receiving circuit is configured to include a light receiving circuit that outputs a signal, an output circuit that performs load switching based on the signal from the light receiving circuit, and the like. This photoelectric switch generally receives power from a DC 12V or 24V power supply line, lowers the voltage to several volts using a series regulator, and then supplies the power to a light projecting circuit or the like.

(Issue 1i to be solved by the invention) In recent years, for example, there has been a tendency to automate production lines in factories by frequently using sensors such as photoelectric switches. A large number of sensors will be connected to the Therefore, the reality is that there is a strong demand for reduced current consumption in sensors such as photoelectric switches.

However, simply suppressing the current flowing into the light emitting element is undesirable because the light emission intensity of the light emitting element decreases, resulting in a decrease in detection sensitivity. In addition, in order to ensure the light emission intensity, it is possible to leave the light emission peak current as it is and reduce the light emission duty ratio, but this would complicate the circuit and make processing of the light reception signal particularly difficult. There are limits to lead to problems. Furthermore, it is possible to use a switching regulator with excellent power efficiency instead of a series regulator, but this would complicate the circuit configuration and increase the number of parts, resulting in an increase in overall size and manufacturing costs. It has the disadvantage of bringing.

SUMMARY OF THE INVENTION An object of the present invention is to provide a photoelectric switch that can reduce current consumption without reducing detection sensitivity or complicating the circuit.

[Configuration of the Invention (Means for Solving the Problem) The photoelectric switch of the present invention includes an oscillation circuit that outputs a light projection signal for determining the light projection timing of a light emitting element, and a switching operation based on the light projection signal. and a step-down switching regulator that performs a switching operation based on the light emitting signal to step down the voltage of the power supply line and supply power to the light emitting circuit. Has characteristics.

(Function) Since the voltage of the power supply line is lowered using a step-down switching regulator, it has superior efficiency and consumes less current than a series regulator. Furthermore, since the switching operation of the switching regulator is performed using a light emission signal originally used to determine the light emission timing, an oscillation circuit dedicated to the switching regulator is not required, and the circuit configuration becomes simple.

Note that as a configuration in which the oscillation circuit is shared, it is also possible to perform the switching operation of the light emitting element by a signal from the oscillation circuit for the switching regulator. However, if the voltage of the power supply line fluctuates, the switching period and duty ratio of the light emitting element will change, causing problems such as poor response and unstable operation as a photoelectric switch. arise.

In this regard, according to the above means, even if there is a voltage fluctuation, there is no fluctuation in the period or duty ratio of the light projection signal, so the responsiveness and stability of the photoelectric switch are not adversely affected. In addition, when the voltage on the power supply line fluctuates, the switching period of the switching regulator is constant, so the voltage applied to the light emitter circuit also fluctuates, but since the light emitting element of the light emitter circuit is driven with a constant current, the luminous intensity There is no risk that the detection characteristics will change due to a change in the detection characteristics.

(Example) An example applied to a reflective photoelectric switch will be described with reference to the drawings. FIG. 1 specifically shows the light emitting side of a photoelectric switch that is directly related to the present invention. 1 is an oscillation circuit for determining the light emission timing of the light emitting element 2;
Outputs a light projection signal S with a constant period. Power line VIN,
A step-down switching regulator 3 is provided to GND, and a light projection circuit 4 is connected to its output line. The light emitting element 2 constituting the light emitting circuit 4 is a light emitting diode, to which a switching transistor 5 to which the light emitting signal S is applied to the base and a current limiting resistor 6 are connected in series. Here, the pulse height of the light emitting signal S is constant, and the base-emitter voltage applied to the transistor 5 when the light emitting signal S becomes high level is constant, so the light emitting element 2 is driven by constant current. be done.

On the other hand, the step-down switching regulator 3 has a general configuration in which a switching transistor 7, a reactor 8, a flywheel diode 9, and a smoothing capacitor 10 are connected as shown. Here, when the transistor 7 is turned on, current flows from the power supply line through the handle 8 into the light projecting circuit 4, and the transistor 7
When the reactor 8 is turned off, the flywheel diode 9 is turned on by the back electromotive force generated in the reactor 8.

Note that an NPN type transistor 11 is inserted into the base circuit of the transistor 7, and this receives the light projection signal S from the oscillation circuit 1 and controls the switching of the transistor 7.

Although not shown, the light receiving circuit 12 includes a light receiving element that receives the pulse tip projected from the light emitting element 2 and reflected by the object to be detected, and amplifies the signal from the light receiving element to emit light from the light emitting element 2. This is a well-known configuration in which the gate circuit is opened and integrated at a timing substantially synchronized with the timing, and the output circuit 13 performs a switching operation on the condition that the integration level reaches a predetermined level. For the above-mentioned synchronous integration, the light emitting signal S is given from the oscillation circuit 1 to the light receiving circuit 12, and the light receiving circuit 12 opens the gate circuit at a timing with a slight delay in the light emitting signal S. .

Now, in the above configuration, the oscillation circuit 1 outputs a pulsed light projection signal S as shown in FIG. 2(A), and when this is at a high level, the step-down switching regulator 3
The transistor 11.7 of the light emitting circuit 4 and the transistor 5 of the light projecting circuit 4 are turned on in synchronization. Therefore, during the period when the light projection signal S is at a high level, current flows from the power supply line Vin through the transistor 7 and the reactor 8 to the light emitting element 2 of the light projection circuit 4, and the light emitting element 2 lights up.

Since this current flows through the axle 8, the current value increases linearly as shown in FIG. 2(B). Furthermore, during the period when the light projection signal S is at a low level, all the transistors 5, 7, and 11 are turned off, so that the light emitting element 2 is turned off. However, since the flywheel diode 9 is turned on by the back electromotive force generated in the reactor 8, the current flowing through the reactor 8 continues to flow as a charging current to the smoothing capacitor 10. In addition, the smoothing capacitor 10
A discharge current flows through when the light emitting element 2 is lit.

Therefore, the output voltage V out appearing on the smoothing capacitor 10 of the step-down switching regulator 3 is approximately half of the input voltage V1n, assuming that ta and tb are approximately equal lengths of time as shown in FIG. (Vout-Vin
/2), and the average output current 10ut is approximately twice the average input current 11n flowing from the power supply line (lout-21
1n). Therefore, even if the lighting current flowing through the light emitting element 2 is set to the same value as the conventional one, in this embodiment, the inflow current from the power line can be suppressed to about half of the conventional one, and especially when multiple photoelectric switches are used, This is suitable in cases where the total current consumption can be kept small. Of course, while producing such excellent effects, the switching regulator 3
Since the configuration uses the oscillation circuit 1 for switching the light emitting element 2 without providing a dedicated oscillation circuit for
The circuit configuration is simple and can be manufactured at low cost.

By the way, in this embodiment, the switching period of the step-down switching regulator 3 is constant, so when there is a voltage fluctuation in the power supply line, the fluctuation rate is equal to the output voltage V o
It appears as is as a rate of change in ut. However, since the light emitting element 2 of the light projecting circuit 4 is driven with a constant current as described above, there is no significant change in the current flowing through the light emitting element 2. Therefore, even if there is a voltage fluctuation in the power supply line, the light emission intensity of the light emitting element 2 can be prevented from changing, and the detection characteristics of the photoelectric switch will not be adversely affected.

Note that as a configuration in which the oscillation circuit is shared as in this embodiment, a configuration in which the switching operation of the light emitting element is performed by a signal from a switching regulator can also be considered. However, with this, if the voltage of the power supply line increases, the switching cycle of the switching regulator becomes longer and the duty ratio becomes smaller, so the light emitting cycle of the light emitting element becomes slower and the light emitting duty becomes shorter. The ratio becomes smaller. However, if the light emitting period of the light emitting element becomes longer, the responsiveness of the photoelectric switch will deteriorate, and if the duty ratio becomes smaller, it will become difficult to amplify the received light signal, resulting in unstable operation. It causes the problem of becoming. In this regard, according to this embodiment, even if there is a voltage fluctuation, the cycle of the light emitting signal does not change, so the responsiveness of the photoelectric switch does not deteriorate, and the duty cycle of the light emitting element 2 does not change. , signal amplification can be performed stably in the light receiving circuit, resulting in stable operation.

Although the above embodiment shows an example in which the present invention is applied to a reflective type photoelectric switch, the present invention is not limited to this, and may be applied to a transparent type charging switch. The present invention may be modified in various ways without departing from the scope of the invention, such as application to a two-wire photoelectric switch that switches power lines.

[Effects of the Invention] As described above, the present invention uses a step-down switching regulator, so it is possible to reduce current consumption, and moreover, the oscillation circuit for the light emitting element is used to perform switching of the switching regulator. Since it is configured to perform this, the circuit configuration is simple, and excellent effects such as no decrease in detection sensitivity or destabilization of operation even if there is a voltage fluctuation in the power supply line are achieved.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and FIG. 1 is a block diagram;
FIG. 2 is a voltage/current waveform diagram. In the drawing, 1 is an oscillation circuit, 2 is a light emitting element, 3 is a step-down switching regulator, 4 is a light emitting circuit, 6 is a current limiting resistor, and 12 is a light receiving circuit. Agent Patent Attorney Tsuyoshi SatoFigure 1Figure 2

Claims (1)

[Claims] 1. An oscillation circuit that outputs a light projection signal for determining the light projection timing of the light emitting element, a light projection circuit that performs a switching operation based on the light projection signal and drives the light emitting element with a constant current, and the light projection signal. A photoelectric switch comprising: a step-down switching regulator that performs a switching operation based on the above to step down the voltage of a power supply line and supply power to the light projecting circuit.