JPH0441633Y2 - - 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 using a self-holding switching element when the load is short-circuited. A short-circuit protection circuit is operated until the power is cut off, and an indicator is provided that continues to indicate the short-circuit condition by blinking at the cycle of the reset time of the power reset circuit and the discharge time of the reset capacitor. It is.

[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 output end may be connected to the power supply terminal 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. In a detection switch having such a short circuit protection circuit, an object detection output is output if there is an object to be detected near the detection switch when normal operation is resumed at the same time as the short circuit in the load is released. However, once a short circuit condition occurs in a device incorporating such a detection switch, it is often necessary to investigate the cause. In such a case, if normal operation is restored by removing the load short circuit, it becomes difficult to investigate the cause of the problem, and there is a problem in that it becomes impossible to ascertain the presence or absence of a short circuit.

[Purpose of invention]

The present invention solves these problems with conventional detection switches, and uses the power display as it is to display a short circuit in the load by flashing the display, and also to release the short circuit in the load. To provide a detection switch which can operate a protection circuit and continue to indicate a short circuit by blinking a display even if the short circuit is detected.

[Structure and effect of the idea]

The present invention is a detection circuit that has a detection circuit that has two output circuits that provide different logical output levels when a detection target is detected, and an output switching element that controls power supply to a load based on the output of the detection circuit. The switch is activated by an overcurrent detection circuit connected in series with the output switching element and the detection output of the overcurrent detection circuit.
A self-holding switching element that shuts off the switching element for output switching, an OR circuit that gives the logical sum output of two types of outputs with different logical output levels of the detection circuit to the self-holding switching element, and a reset capacitor are connected to the power supply. A power supply reset circuit that inhibits the detection circuit output for a predetermined prohibition time during the voltage reset time after power on and when the supply voltage to the detection circuit drops, and a power supply reset circuit that is connected to both ends of the detection circuit power supply and lights up when power is supplied to the detection circuit. In addition, the present invention is characterized by comprising an indicator which, when a short circuit is detected, blinks at a period based on the discharging time of the reset capacitor of the power supply reset circuit and the prohibition time to notify the short circuit state.

According to the present invention having such features, when a short circuit occurs, the self-holding switching element is driven to operate the short circuit protection circuit. Thereafter, the current supply circuit maintains the protection, so that even if the short-circuited state of the load is released, the protection operation can be continued. In addition, since the power supply input voltage can be lowered by outputting the logical sum of two types of logical output levels regardless of the presence or absence of the object to be detected, it is possible to continue the short-circuit state on the detection circuit side. Therefore, the indicator flashes according to the cycle of the discharging time of the capacitor connected to the power supply reset circuit and the inhibition time, and the short circuit display can be continued.

[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 power supply circuit 9 is connected between the output terminals 1 and 2, which has a Zener diode 7 and a transistor 8, and outputs a constant voltage Vc when the current is below a predetermined value, and has constant current characteristics when the current is higher than that. The power supply circuit 9 supplies a constant voltage to the detection circuit 10 formed as an IC. A smoothing capacitor C is connected between the power supply terminals of the detection circuit 10.
11 and a series connection body of a resistor 12, a Zener diode 13, and a light emitting diode 14, which serve as a current limiting circuit, are connected in parallel. A resonant circuit including a detection coil 15 and a capacitor C16 is connected to the detection circuit 10, and includes an oscillation circuit 10a and a comparison circuit 10b that detects an object based on a decrease in the output of the oscillation circuit 10a. The output of the detection circuit 10 is applied directly and via an inverter 10e to an NL output circuit 10c and an NH output circuit 10d. These output circuits 1
0c and 10d are “L” when an object is detected respectively.
This is an output circuit that outputs level and "H" level, respectively. In addition, the detection circuit 10 is equipped with a power source that turns off both output circuits 10c and 10d during the power reset time after power on and the prohibition time after short circuit detection, so as not to output an incorrect output to the outside immediately after power is turned on. A reset circuit 10f is provided. The power supply reset circuit 10f is externally provided with a power supply reset time, which is the charging time from 0V to the power supply reset release voltage Vre, and an inhibition time, which is the charging time from the reset initial voltage Vs, which starts the reset operation, to the power supply reset release voltage Vre. A reset capacitor C17 that defines T1 is connected. The terminal voltage of the power supply reset circuit 10f is the power supply reset release voltage.
The output circuit is turned off during the power reset time and prohibition time until Vre is reached. The output terminal of the NL output circuit 10c is a light emitting diode 18,
It is connected to the base of the output switching transistor 5 via a constant current circuit 19. Also, NL output circuit 10
The output ends of the C and NH output circuits 10d are connected to the anode of a thyristor 22 via diodes 20 and 21, respectively. The anode of the thyristor 22 is connected from the terminal 1 to a constant current holding circuit formed by an FET 23. The thyristor 22 has its gate 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.

Next, FIG. 3 is a circuit diagram showing the configuration of the output circuit section of the detection circuit 10. As shown in this figure, output circuits 10c and 10d have the same configuration. In this figure, the detection signal is applied to transistor Q4 via transistor Q1 and inverter 10e of the NL output circuit. Transistors Q1 and Q4 are switching transistors that turn off when an "H" level detection output is applied, and their collector and emitter terminals are connected to output transistors Q2, Q3 and Q5, Q6, respectively. Reference numerals 30 and 31 are constant current sources that selectively supply a constant current to the transistors Q1 or Q4 and Q2 or Q5, and are used in the power supply reset circuit 10f described above.
controlled by

(Operation of this embodiment) Now, connect the DC power supply 32 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. Then, the oscillation circuit 1 in the detection circuit 10 is generated by a resonant circuit formed by the detection coil 15 and the capacitor C16 connected to the detection circuit 10.
0a oscillates and is in a standby state waiting for an object to approach.

Now, when an object approaches and the oscillation output of the oscillation circuit 10a decreases and a detection signal is given to the output circuit from the comparator circuit 10b, the transistor Q1 of the NL output circuit 10c turns off, transistor Q2 turns on, and the NL output terminal becomes "H". ” level, and the emitter current of transistor Q2 flows through light emitting diode 18 and constant current circuit 1.
9 into the base of transistor 5, turning transistor 5 on. 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 18 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 of FIG. 4. Proximity switch detection coil 1
If the load L is short-circuited at time t1 when there is an object to be detected near 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 thyristor 22 increases and the thyristor 22 is turned on. Then, current flows out from the transistor Q2 of the NL output circuit 10c via the diode 20 and the thyristor 22, and the output transistor 5
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 Q2, the forward drop voltage of the diode 20, and the anode-cathode voltage of the thyristor 22. Become. Therefore, the voltage Vf of the power 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 of 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. 4c. At this time, as shown in FIG. 4b, the capacitor C17 forming the power supply reset circuit 10f is also discharged.
The input terminal voltage of the power supply reset circuit 10f of the detection circuit 10 gradually decreases. Then, at time t2 when the power supply reset initial voltage Vs of the detection circuit 10 is reached,
Both transistors Q2 and Q3 of the NL output circuit 10c are turned off, and no current flows out from the output terminal NL. Therefore, the power input terminal of the detection circuit 10
Vcc returns to the terminal voltage Vc when the load is not short-circuited, as shown in FIG.
The light emitting diode 14 lights up. Then the fourth
As shown in FIG. b, the capacitor C17 connected to the power supply reset circuit 10f is charged again. Then, output is prohibited for a prohibition time T1 until the power supply reset release voltage Vre is reached.
However, the thyristor 22 is as shown in FIG.
It continues to be on due to the holding current from FET23. And the voltage Vre of the power supply reset terminal R
At time t3, the power supply reset circuit 10f releases the inhibition of the NL output circuit 10c.
Therefore, as in the case of detecting a short circuit, the NL output circuit 10c
A current flows out from the transistor Q2, and the voltage at the power input terminal of the detection circuit 10 becomes Vf again. In this way, as shown in FIG. 4a, the power supply voltage of the detection circuit 10 rises and falls repeatedly in a predetermined cycle, and as a result, as shown in FIG. 4c, the light emitting diode 14
flashes. This cycle is the charging and discharging time of the reset capacitor C17, that is, the capacitor C17
It is possible to adjust the capacity by the resistance value connected to the charging circuit or the discharging circuit.

If the detected object moves away, the output circuit of the detection circuit 10 returns to its original state, and the output terminal of the NL output circuit becomes "L" level. Also NH output circuit 10
d transistor Q5 is driven. At this time, the power supply terminal Vcc of the detection circuit 10 is the collector-emitter voltage Vce when the transistor Q5 is conductive, the forward drop voltage of the diode 21, and the thyristor 2.
This is the sum of the two anode-cathode voltages, and has the same value as the voltage Vf described above. Therefore, the voltage at the power supply terminal of the detection circuit 10 changes in the same manner as shown in FIG.
The capacitor C17 also gradually discharges. When the power supply reset initial voltage Vs is reached, the inhibition of output is similarly canceled after the power supply inhibition time T1 has elapsed.
Then, the terminal voltage of the detection circuit 10 becomes Vf again and the same operation is repeated thereafter. Therefore, even in this case, it is possible to continue blinking the light emitting diode 14.

In this embodiment, a DC three-wire proximity switch was explained, but it can also be applied to a detection switch such as a photoelectric switch, and the output transistor can also be applied to all combinations of PNP and NPN transistors. It is.

[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 detection circuit 1.
FIG. 4 is a circuit diagram showing the configuration of the output circuit in 0, and FIG. 4 is a waveform diagram showing waveforms of various parts in a load short-circuit state. 1, 2, 24...terminal, 5, 8, Q1~Q6...
...Transistor, 10...Detection circuit, 10a...
Oscillation circuit, 10b...Comparison circuit, 10c...NL
Output circuit, 10d...NH output circuit, 10f...
Power reset circuit, 14, 18...Light emitting diode, C11, C16, C17...Capacitor,
6, 12...Resistor, 22...Thyristor.

Claims (1)

[Claims for Utility Model Registration] A detection circuit having two output circuits that provide different logical output levels when a detection target is detected, and an output switching element that controls power supply to a load based on the output of the detection circuit. A detection switch comprising: an overcurrent detection circuit connected in series to the output switching element; and a self-holding switching device that is activated by the detection output of the overcurrent detection circuit and shuts off the output switching element. an OR circuit that provides a logical sum output of two types of outputs of different logic output levels of the detection circuit to the self-holding switching element; and a reset capacitor connected to the detection circuit to determine the voltage reset time after power is turned on and the detection circuit. a power supply reset circuit that inhibits the output of the detection circuit for a predetermined prohibition time when the supply voltage to the detection circuit decreases; 1. A detection switch comprising: an indicator that blinks at a cycle based on the discharging time and prohibition time of a reset capacitor of a power supply reset circuit to notify a short circuit state.