JPS63160413A - Contactless two-wire ac switch - Google Patents

Abstract

PURPOSE:To attain mass-production by connecting a thyristor to a gate of a FET and connecting a thyristor in parallel with a Zener diode, connecting the thyristor to a switching circuit and connecting an overcurrent sensing element in series with the switching circuit. CONSTITUTION:When a detection signal is outputted from a detection circuit 10, a switching element TR3 is cut off and the source potential of a MOS.FET 19 rises, a thyristor 12 connected in parallel with a Zener diode ZD2 is triggered and conducted, the switching circuit TR1 is conducted to drive the load through the reception. In such a case, when an overcurrent flows in the circuit of the AC 2-wire contactless switch, the overcurrent sensing element R4 detects the overcurrent. The thyristor 13 connected to the gate of the MOS.FET9 is triggered and conducted. The gate potential of the FET9 is fallen down nearly zero and the FET is cut off. Thus, since the voltage is not supplied from the FET to the switching circuit via the thyristor 13, the switching circuit TR 1 is cut off and the overcurrent is shut off.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an AC two-wire non-contact switch that is connected between a load and an AC power source and shares a detection signal line and an AC power line, and particularly relates to an overcurrent protection function. The present invention relates to an AC two-wire non-contact switch that is equipped with the following features and has low leakage current and residual voltage.

[Conventional technology]

AC 2-wire non-contact switch is a photoelectric switch.

The internal driving power of a non-contact switch such as a proximity switch is supplied from two signal output lines connected to a detection signal output end, instead of relying on an independent AC power supply line. Therefore, the power supply to the load can be switched and controlled by simply connecting the detection signal output terminal between the AC power source and the load. It is possible to use

However, with AC 2-wire non-contact switches, it is necessary to supply driving power to the non-contact switch even when no detection signal is output, so it is theoretically impossible to prevent leakage current that occurs at the detection signal output terminal at this time. It's impossible. Moreover, since it is necessary to supply driving power in the same way even when the detection signal is not output, it is similarly impossible to prevent some voltage from remaining at both ends of the detection signal output terminal. However, the smaller the leakage current and residual voltage, the better the operating characteristics, so it has been desired to reduce these.

As a technology to solve this problem,
The one disclosed in Publication No. 37 has been proposed. This technology is a MOS-N channel as shown in Figure 2.
Enhancement type F E 71 T-cross! By using it in the constant voltage circuit of a two-wire non-contact switch, it is intended to reduce leakage current and residual voltage. That is, M
Since the OS-FET1 can increase the input impedance of the gate and therefore increase the resistance value of the resistor R1, leakage current when no detection signal is output can be reduced.

Also, the impedance when MOS-FETI is conductive is 1
Since it is very small at 0 to 20Ω, the residual voltage when the detection signal is output can also be reduced.

In addition, in an AC two-wire type non-contact switch, the load may become internally short-circuited due to an accident, or an operator may mistakenly connect the AC power source to the non-contact switch without connecting the proper load. In order to protect the internal circuit from such a short-circuit condition, an overcurrent protection circuit may be provided inside the non-contact switch. However, in this case, if the operation of the protection circuit is slow, there is a problem in that the overcurrent will continue to flow through the switching element etc. until the overcurrent protection is activated, leading to destruction of the switching element etc.

Therefore, in order to prevent overcurrent, a contactless switch in which a current limiting resistor is connected in series with a switching element has been proposed. However, the power capacity of this resistor must be large, and its shape also becomes large, making it difficult to downsize the entire non-contact switch.

In order to solve this problem, Japanese Patent Application Laid-Open No. 60-150318
A technique disclosed in the above publication has been proposed.

As shown in Figure 3, this technology uses overcurrent detection resistor R2.
By providing a thyristor 2 and a thyristor 2, overcurrent protection is provided for the AC two-wire non-contact switch.

That is, when an overcurrent flows through the load 3, the voltage across the resistor Rx increases, so the thyristor 2 is triggered and becomes conductive. Therefore, the gate potential of the MOS-FET 4 drops to near zero, and the FET 4 is cut off. Therefore, overcurrent is subject to current restriction and is instantaneously cut off.

[Problem that the invention seeks to solve]

However, these two conventional techniques have the following problems. First of all, in the technology disclosed in Japanese Utility Model Application Publication No. 59-59037 (see Figure 2), since there are variations in the threshold voltage values of MOS/FETI, this cannot be done in individual AC 2-wire non-contact switches. Zener diode ZD compatible with threshold voltage values.

There is a problem in that it is not suitable for mass production because the Zener voltage must be selected for each.

Next, the technique disclosed in Japanese Patent Application Laid-Open No. 150318/1983 (see FIG. 3) also has the same problem as above because the threshold voltage value of the MOS-FET 4 used varies. In addition, this technology has the following problems. The resistance elements in this circuit when the detection signal is output are three elements: the MOS-FET 4, the thyristor 14, and the overcurrent detection resistor R2. but,
The resistance value of the thyristor 14 when it is conductive and the resistance value of the resistor R2 are so small that they can be almost ignored. Therefore FET
The resistance value of this circuit when the detection signal is output is determined only by the resistance value when the circuit 4 is conductive. Generally, MOS-FETs are formed by connecting a large number of cells in parallel on a chip in order to reduce the resistance value when conducting. Therefore, F
In order to reduce the resistance value of ET4, it is necessary to connect a larger number of cells in parallel, leading to an increase in cost due to an increase in chip area.

This invention was made in view of the above-mentioned problems, and is equipped with an overcurrent protection function, has no restrictions on the selection of MOS/FET, and has low leakage current and residual voltage.
The purpose is to provide wire type non-contact switches.

[Means for solving problems]

Specific means for solving the above problems and achieving this objective include: a constant voltage circuit that receives power supply and outputs a constant voltage; a detection circuit that outputs a detection signal when an object to be detected approaches or moves away; A switching element that conducts or cuts off current according to this detection signal, a switching circuit that controls the load by conducting or cutting off the switching element, and a smoothing capacitor that supplies voltage to the detection circuit when the load is driven. In an AC 2-wire non-contact switch having 1. The constant voltage circuit includes a MOS-FB, T and a Zener diode connected to the source of the FET, a thyristor is connected to the gate of the FET, a thyristor is connected in parallel to the Zener diode, and the thyristor is connected to the Zener diode. It is connected to a switching circuit, and an overcurrent detection element is connected in series with this switching circuit.

[For production]

Since this invention employs the above-mentioned means, the following effects are brought about. When the detection circuit is not outputting a detection signal, the switching element is conductive and the MOS-PE
Since the gate potential of T is controlled by the voltage determined by the Zener diode connected to the source, it outputs a constant voltage and supplies it to the detection circuit.

Next, when the detection circuit outputs a detection signal, the switching element is cut off. Then, the source potential of the MOS-FET rises, and the thyristor connected in parallel to the Zener diode is triggered and becomes conductive.

In response to this, the switching circuit becomes conductive and drives the load.

In this case, the load may become internally short-circuited due to an accident, or
Alternatively, if a worker accidentally connects an AC power source to a non-contact switch without connecting the proper load and an overcurrent flows into the circuit of the AC 2-wire non-contact switch, the overcurrent detection element will detect the overcurrent. do. In response to this, MOS-FE
The thyristor connected to the gate of T is triggered to conduct. Due to this conduction, the gate potential of the FET drops to near zero and the FET is cut off. Therefore, FET is used in the switching circuit.
Since no voltage is supplied from the thyristor through the thyristor, the switching circuit is also cut off and the overcurrent is cut off.

〔Example〕

This invention will be explained in detail below based on one embodiment.

Note that the same parts as in the conventional example are given the same symbols to simplify the explanation.

As shown in FIG. 1, in the AC two-wire type non-contact switch according to the present invention, a diode bridge circuit 8 is connected between output terminals 5 and 6, and an AC power source 7 is connected externally via a load 3. has been done.

Between the positive and negative sides of the diode bridge circuit 8, there is a MOS-F with enhancement characteristics, which is the main component of the constant voltage circuit.
ET9, a detection circuit 10 that outputs a detection signal when the detection target approaches or separates, an oscillation circuit 11 that oscillates when the detection target approaches, a Zener diode ZDt connected to the source of the FET9, and this Zener diode ZD.
, a thyristor 12 connected in parallel to the thyristor 13 connected to the gate of the FET 9, and a detection circuit 1 when driving a load.
Smoothing capacitor C, which supplies voltage to 0, transistor Trt, which is an open/close circuit, transistor Tri, which is a switching element, transistor Tr2, which is conductive only when this transistor Trl is conductive, transmits the DC voltage of smoothing capacitor C1 to the gate of FET9. Diode D1
and a resistor R55, a diode D2 connected between the source of the FET9 and the detection circuit 10, a resistor R4 which is an overcurrent detection element connected to the emitter of the transistor Tr+, and resistors R3, R5, R,, R,, R, It is connected.

The operation of this circuit having such a configuration will be explained below. First, if the object to be detected is separated, the oscillation circuit 11 oscillates, and the detection circuit 10 does not output a detection signal. Therefore, the output signal of the detection circuit 10 becomes HIGH, and the transistor Tr3, which is a switching element, is supplied with a base current and becomes conductive. In response to this, transistor Tr2
It also conducts. Therefore, the source potential of the MOS-FET 9 rises, and the gate potential also rises accordingly. In this case, if the gate potential of FET9 attempts to exceed the sum of the Zener voltage of the Zener diode ZDz, the base-emitter voltage of the transistor Tr2, and the collector-emitter voltage of the transistor Tr, the gate potential begins to decrease and stabilizes at a constant value determined by the relationship with the source potential. Therefore, FET 9 supplies a constant voltage to detection circuit 10 .

Next, when the detection target approaches and the oscillation circuit 11 stops oscillating, the detection circuit IO outputs a detection signal.

Therefore, since the output signal of the detection circuit 10 becomes LOW, the transistor Tr3 is cut off, and accordingly, the transistor Trz is also cut off. Then MOS・FET9
The source potential of FET 9 rises, and when the source potential of FET 9 exceeds the sum of the Zener voltage of Zener diode ZD2, the trigger voltage of thyristor 12, and the base-emitter voltage of transistor Tr+, which is an open/close circuit, the thyristor 12 is triggered and becomes conductive. Transistor Tr+ is supplied with base current, so it becomes conductive, and load 3 is driven.

In this state, a case where the load 3 is short-circuited due to an accident or a misconnection by the operator, and an overcurrent flows into the non-contact switch will be described below. Due to the inflow of overcurrent, the voltage across the resistor R4, which is an overcurrent detection element, increases, and the thyristor 13 is triggered and becomes conductive. Due to this conduction, the potential of the gate of MOS-FET9 drops to near zero,
FET9 is cut off. Then, since the supply of base current is cut off, the transistor Tr is also cut off, and the inflow of overcurrent is instantly prevented.

In this embodiment, the transistor Tr is used in the switching circuit that switches the load, so the on-resistance (resistance value when conducting) can be reduced, and it is inexpensive to use as the MOS-FET9, which is the main component of the constant voltage circuit. can be used to reduce costs.

〔Effect of the invention〕

As is clear from the above description, the present invention includes a constant voltage circuit that receives power supply and outputs a constant voltage, a detection circuit that outputs a detection signal depending on the proximity or separation of a detection target,
A switching element that conducts or cuts off current according to this detection signal, a switching circuit that controls the load by conducting or cutting off the switching element, and a smoothing capacitor that supplies voltage to the detection circuit when the load is driven. In the AC two-wire non-contact switch, the constant voltage circuit includes a MOS-FET and a Zener diode connected to the source of the FET, a thyristor is connected to the gate of the FET, and the thyristor is connected in parallel to the Zener diode. Since the thyristor is connected to the switching circuit, and the overcurrent detection element is connected in series to the switching circuit, the gate potential can be controlled by the source potential of the MOS-FET. Therefore, even if there are variations in the characteristics of the FET elements themselves, each FET operates with a gate potential that corresponds to the source potential of each FET. Therefore, since there is no need to select a Zener diode that corresponds to the characteristics of each FET, mass production of AC two-wire type non-contact switches is possible.

Furthermore, since only one Zener diode is used, there is almost no difference in the constant voltage supplied to the detection circuit when a detection signal is output and when it is not output, and stable detection operation is possible at all times. Furthermore, since an overcurrent detection element is used, overcurrent protection can be achieved. Furthermore, MOS-
Since FETs are used, leakage current and residual voltage are reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of an AC two-wire non-contact switch according to the present invention, and FIGS. 2 and 3 are circuit diagrams of a conventional example. 3...Load, 7...AC power supply (power supply), 9...M
OS/FET (constant voltage circuit), engineering 0...detection circuit, 1
2.13... Thyristor, Tr,... Transistor (switching circuit), Tr,... Transistor (switching element), CI... Smoothing capacitor, ZDz... Zener diode (constant voltage circuit), R4 ...Resistance (overcurrent detection element).

Claims (1)

[Claims] (1) A constant voltage circuit that receives power supply and outputs a constant voltage, a detection circuit that outputs a detection signal when an object to be detected approaches or moves away from it, and a switching element that conducts or interrupts current according to this detection signal. , an AC two-wire contactless switch having a switching circuit that controls a load by conducting or cutting off the switching element, and a smoothing capacitor that supplies voltage to the detection circuit when driving the load, wherein the constant voltage circuit is a MOS・FET (Metal Oxygen
-de Semiconductor・Field E
effect Transistor) and this MOS
- A Zener diode is connected to the source of the FET, a thyristor is connected to the gate of the MOS FET, a thyristor is connected in parallel to the Zener diode, and the thyristor is connected to the switching circuit, and An AC two-wire non-contact switch characterized in that an overcurrent detection element is connected in series to this switching circuit.