JPH0416506Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of the Invention] The present invention relates to a detection switch such as a photoelectric switch or a proximity switch having a short circuit protection function.

[Summary of the idea]

The detection switch according to the present invention is used in electronic switches such as photoelectric switches and proximity switches by providing a display element at the power input terminal of the detection circuit to indicate that the power has been turned on, and to display the reset time and reset time of the power reset circuit when the load is short-circuited. The number of indicators is reduced by providing an indicator that blinks in accordance with the period of discharge time of the capacitor to indicate a short circuit state.

[Prior art and its problems]

A conventional electronic switch has a detection section and a switching element such as a thyristor, and is configured such that the switching element is driven based on a detection output to control the supply of power to a load. However, if the load becomes internally short-circuited due to an accident, or by mistake, the power source may be connected directly to the detection switch without connecting the load. In order to protect the internal circuit from such a short-circuit condition, a protection circuit for short-circuit protection is provided inside the detection switch. By the way, if the short-circuit protection circuit is operating when the load is short-circuited, it is necessary to notify the short-circuit state. Therefore, the detection switch requires an indicator to indicate the short circuit state in addition to a power indicator and an operation indicator. When the number of indicators increases in this manner, it becomes difficult to understand what the lights on the indicators indicate, and there is a problem in that it becomes difficult to understand at first glance that it is a short-circuit protection warning.

[Purpose of invention]

The present invention solves the problems of conventional detection switches, and provides a detection switch that can clearly indicate the short-circuit condition of the load by using the power supply display as is and making the display blink. It provides:

[Structure and effect of the idea]

The present invention is a detection switch that has a detection circuit and an output switching element that controls power supply to a load based on the output of the detection circuit, and an overload switch that is connected in series to the output switching element. A self-holding switching element that is driven by the current detection circuit and the detection output of the overcurrent detection circuit and cuts off the output switching element, and a reset capacitor connected to the voltage reset time after the power is turned on and the supply to the detection circuit. A power supply reset circuit that inhibits the detection circuit output for a predetermined prohibition time when the voltage drops, and a power supply reset circuit that is connected to both ends of the power supply of the detection circuit and lights up when power is supplied to the detection circuit, and that is used to reset the power supply reset circuit when a short circuit is detected. The present invention is characterized by comprising an indicator that blinks at a period based on the discharge time of the capacitor and the inhibition time to notify the short circuit state.

According to the present invention having such features, when a short circuit occurs, the display is made to blink according to the cycle of the discharging time of the capacitor connected to the power supply reset circuit and the inhibition time. Therefore, it is possible to display a short circuit using the power supply display as is.

[Explanation of Examples]

(Configuration of Embodiment) FIG. 1 is a block diagram schematically showing an embodiment of a DC three-wire proximity switch according to the present invention, and FIG. 2 is a circuit diagram showing its detailed configuration. In this figure, a constant current source 3 and a diode 4 are connected between terminals 1 and 2, and a transistor 5, which is an output switching element, and an overcurrent detection resistor 6 are connected in series. A constant voltage power supply circuit 9 consisting of a Zener diode 7 and a transistor 8 is also connected between the output terminals 1 and 2. The power supply circuit 9 supplies a constant voltage to the detection circuit 10 formed as an IC. A smoothing capacitor C11, a resistor 12 serving as a current limiting circuit, a series connection body of a Zener diode 13 and a light emitting diode 14 are connected in parallel between the power supply terminals of the detection circuit 10. A resonant circuit including a detection coil 15 and a capacitor C16 is connected to the detection circuit 10, and is provided with an oscillation circuit and a comparison circuit section that detects an object based on a decrease in the output of the oscillation circuit. The output section of the detection circuit 10 is provided with a series connection of output transistors Q1 and Q2 between the power supplies, and a transistor Q0 that drives these transistors based on an object detection signal. Q1 is turned on when an object is detected. An output circuit is formed that turns on Q2 when not detected. In addition, the power supply reset time after power-on is set to prevent incorrect output from being output externally when the output voltage rises after power-on.
A power supply reset circuit 17 is also provided which turns off both of these output transistors Q1 and Q2 during a prohibited time after a short circuit is detected. The power supply reset circuit 17 has an external power supply reset release voltage from 0V.
Power supply reset time, which is the charging time to Vre, and reset initial voltage Vs, which starts the reset operation.
The reset capacitor C defines the prohibition time, which is the charging time from Vre to the power supply reset release voltage Vre.
18 are connected. The power supply reset circuit 17 stops the operation of the constant current circuit 19 for the power supply reset time and prohibition time until the terminal voltage reaches the power supply reset release voltage Vre, and resets the transistors Q1 and Q.
2 is turned off. The midpoint of transistors Q1 and Q2 is an NL output terminal that outputs an "L" level when the detection circuit 10 does not detect an object, and outputs an "H" level when an object is detected.
It is connected to the base of the output switching transistor 5 via a light emitting diode 20 and a constant current circuit 21, and further connected to the anode of a thyristor 23 via a diode 22. Further, the gate of the thyristor 23 is connected to a common connection terminal between the emitter of the transistor 5 and the resistor 6, and controls to detect an overcurrent and turn off the output circuit.

(Operation of this embodiment) Now, connect the DC power supply 30 between terminals 1 and 2 as shown in the figure.
A load L is connected between the terminal 1 and the collector terminal 24 of the transistor 5. Then, the constant voltage Vc is supplied from the power supply circuit 9 to the detection circuit 10. At the same time, current flows to the light emitting diode 14 via the Zener diode 13, and the light emitting diode 14 lights up continuously, indicating that power is being supplied. The oscillator of the detection circuit 10 oscillates due to the resonance circuit formed by the detection coil 15 and the capacitor C16 connected to the detection circuit 10, and is in a standby state awaiting the approach of an object.

Now, suppose that the oscillation output of the detection circuit 10 decreases due to the proximity of an object, the detection output turns off the transistor Q0 and turns on the output transistor Q1, causing the output terminal NL of the detection circuit 10 to go to "H" level, causing the output from the transistor Q1 to turn off. The emitter current flows into the base of the transistor 5 via the light emitting diode 20 and the constant current circuit 21, turning on the transistor 5. Then, since the collector voltage decreases, power is supplied to the load L and the load L is driven. At this time, the light emitting diode 20 lights up to indicate that the proximity switch is in a detection state in which it has detected an object.

(Operation when short-circuited) Now, the operation when an overcurrent flows through the load L or when the load L is short-circuited will be explained with reference to the waveform diagram in FIG. 3. Proximity switch detection coil 1
If the load L is short-circuited at time t1 when there is an object to be detected in the vicinity of the output transistor 5, an overcurrent momentarily flows through the output transistor 5 and the resistor 6. For this reason, thyristor 2
The gate voltage of No. 3 increases and the thyristor 23 turns on. Then, the emitter current of the transistor Q1 of the detection circuit 10 flows out through the diode 22 and the thyristor 23, and the output transistor Q1 flows out through the diode 22 and the thyristor 23.
is in the off state. At this time, if the voltage at the power supply input terminal Vcc of the detection circuit 10 is Vf, the voltage Vf is the sum of the collector-emitter voltage Vce of the transistor Q1, the forward drop voltage of the diode 22, and the anode-cathode voltage of the thyristor 23. . Therefore, the voltage at the power supply input terminal Vcc of the detection circuit 10 becomes low due to the short circuit of the load L, and becomes lower than the terminal voltage Vr at the input terminal R of the power supply reset circuit 17 (Vc>Vr>Vf). Then, as the voltage at the power input terminal Vcc of the detection circuit 10 decreases, the light emitting diode 14 is turned off as shown in FIG. 3c. At this time, the third
As shown in FIG. b, since the capacitor C18 forming the power supply reset circuit 17 is also discharged, the input terminal voltage of the power supply reset circuit 17 of the detection circuit 10 gradually decreases. At time t2 when the power supply reset initial voltage Vs of the detection circuit 10 is reached, both transistors Q1 and Q2 of the detection circuit 10 are turned off, and no current flows out from the output terminal NL.
Therefore, the power input terminal Vcc of the detection circuit 10 returns to the terminal voltage Vc when the load is not short-circuited, as shown in FIG. 3a, and therefore the current limiting resistor R
12, a current flows through the display circuit consisting of the Zener diode 13 and the light emitting diode 14, and the light emitting diode 14 lights up. Then, as shown in FIG. 3b, the capacitor C18 connected to the power supply reset circuit 17 will be charged again. Then, output is prohibited for a prohibition time T1 until the power supply reset release voltage Vre is reached, and the prohibition of output is canceled at time t3. Therefore, transistor 5 is momentarily turned on and overcurrent is detected. After this, the state becomes the same as the initial state before the short circuit, and current flows out from the transistor Q1 of the detection circuit 10, turning on the transistor 5 and causing an overcurrent to flow. However, since the voltage across the overcurrent detection resistor 6 increases, the thyristor 23 is turned off, and the emitter current of the transistor Q1 flows to the anode side of the thyristor 23. Therefore, the terminal voltage of the detection circuit 10 decreases to Vf again. Therefore, as shown in FIG. 3a, the power supply voltage of the detection circuit 10 rises and falls repeatedly in a predetermined cycle, and accordingly, the light emitting diode 14 blinks as shown in FIG. 3c.
This cycle can be adjusted by the charging/discharging time of the reset capacitor C18, that is, by the capacitance of the capacitor C18 and the resistance value connected to the charging circuit or the discharging circuit. If the short-circuit condition is eliminated here, the thyristor 23 will not be triggered, so that the load L can be normally driven by the output transistor 5.

In this embodiment, the output of the detection circuit is the NL output, which is at the "L" level when no object is detected, but the same configuration can be made by using the NH output, which is at the "H" level when no object is detected. It is possible. Although the DC three-wire proximity switch has been described, it can be applied to detection switches such as photoelectric switches, and output transistors can be applied to all combinations of PNP and NPN transistors.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an overview of one embodiment of the DC three-wire proximity switch according to the present invention, Fig. 2 is a circuit diagram showing its detailed configuration, and Fig. 3 is a waveform showing waveforms of various parts in a load short-circuit state. It is a diagram. 1, 2, 24... terminal, 5, 8, Q0, Q1,
Q2...Transistor, 10...Detection circuit, 1
4, 20... Light emitting diode, C11, C16,
C17...Capacitor, 17...Power reset circuit, 6, 12...Resistor, 23...Thyristor.

Claims (1)

[Claims for Utility Model Registration] (1) A detection switch comprising a detection circuit and an output switching element that controls power supply to a load based on the output of the detection circuit, the output switching element an overcurrent detection circuit connected in series with the overcurrent detection circuit, a self-holding switching element that is driven by the detection output of the overcurrent detection circuit and cuts off the output switching element, and a reset capacitor that is connected to the voltage after the power is turned on. a power supply reset circuit that inhibits the detection circuit output for a predetermined prohibition time when the voltage supplied to the detection circuit decreases during the reset time; and a power supply reset circuit that is connected to both ends of the power supply of the detection circuit and lights up when power is supplied to the detection circuit. and an indicator that, when a short circuit is detected, blinks at a cycle based on the discharge time and prohibition time of the reset capacitor of the power supply reset circuit to notify the short circuit state;
A detection switch comprising: (2) The detection switch according to claim 1, wherein the indicator is a light emitting diode.