JP2696168B2 - AC 2-wire non-contact switch - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC two-wire contactless switch that is connected between a load and an AC power supply and shares a detection signal line and an AC power supply line. The present invention relates to an AC two-wire non-contact switch in which a malfunction is less likely to occur and a leakage current and a residual voltage are small. [Prior Art] An AC two-wire contactless switch is a device in which an internal drive power supply of a contactless switch such as a photoelectric switch or a proximity switch is connected to a detection signal output terminal without using an independent AC power supply line.
The signal is supplied from the signal output line. Therefore, the switching control of the power supply to the load can be performed simply by connecting the detection signal output terminal to the terminal between the AC power supply and the load. It is possible to use switches. However, since the AC two-wire contactless switch needs to supply drive power to the contactless switch even when the detection signal is not output, it is theoretically necessary to prevent leakage current generated at the detection signal output terminal at this time. Impossible. Also,
Since it is necessary to supply the driving power similarly when the detection signal is output, it is similarly impossible to prevent a slight voltage from remaining at both ends of the detection signal output terminal. However, since the smaller the leakage current and the residual voltage, the better the operation characteristics, it has been desired to reduce these. As the first technology to solve this problem, the actual technology
The one disclosed in 59037 has been proposed.
This technology uses a MOS N-channel
By using the enhancement type FET1 in the constant voltage circuit of the AC two-wire contactless switch, reduction of leakage current and residual voltage is intended. That is, since the MOS • FET ₁ can increase the input impedance of the gate and thereby increase the resistance value of the resistor R ₁ , the leakage current of a value at which no detection signal is output can be reduced. MOS ・ FET1
Has a very small impedance of 1.4 to 3 .OMEGA., So that the residual voltage when the detection signal is output can be reduced. As a second technique for solving the above-described problem, the following technique has been proposed. As shown in FIG.
A diode bridge circuit 8 is connected between the terminals 6 and an AC power supply 7 is connected to the outside via the load 3. Between the positive and negative sides of the diode bridge circuit 8, the enhancement specific MOS / FET which is a main component of the constant voltage circuit is provided.
9, the oscillation circuit 11, the Zener diode ZD ₂ connected to FET9 source of the detection circuit 10 for outputting a detection signal by the proximity or away from the detection object, the oscillation by the proximity of the detection target performs, in parallel to the Zener diode ZD ₂ Thyristor 12 connected, thyristor 13 connected to the gate of FET 9, smoothing capacitor that supplies voltage to detection circuit 10 when driving a load
C _1, open circuit transistor Tr ₁ is, the transistor Tr ₃ is a switching element, transistor Tr ₂ which conducts only during the conduction of the transistor Tr _3, the smoothing capacitor C ₁
Is the diode D ₁ and the resistor R _8, the source and detector diode connected D ₂ between 10 FET9, overcurrent detection element connected to the emitter of the transistor Tr ₁ is transmitted to the gate of FET9 a direct current of Resistance R ₄ , and resistances R ₃ , R ₅ , R ₆ , R
₇ is connected. The operation of this circuit having such a configuration will be described below. First, when the detection target is separated, the oscillation circuit 11 does not oscillate, and the detection circuit 10 does not output a detection signal. Therefore, the output signal of the detection circuit 10 becomes HIGH, the transistor Tr ₃ is a switching element turned supplied base current. In response to this transistor Tr ₂ is also turned on.
Therefore, the source potential of the MOSFET 9 rises, and the gate potential rises accordingly. Zener voltage of this Zener diode ZD _2, transistor Tr base-emitter voltage of _2, and when the sum of the respective voltage value of the collector-emitter voltage of the transistor Tr ₃ is the gate potential of FET9 to about to exceed the gate voltage Begins to decrease and stabilizes at a constant value determined in relation to the source potential. Therefore FET9
Supplies a constant voltage to the detection circuit 10. Next, when the oscillation circuit 11 starts oscillating due to the detection target approaching, the detection circuit 10 outputs a detection signal. Therefore,
Since the output signal of the detection circuit 10 becomes LOW, the transistor T
r ₃ is cut off, the transistor Tr ₂ Accordingly also cut off. Then the source potential of the MOS-FET9 rises, the Zener diode ZD ₂ zener voltage, the sum FET9 source of each of the voltage value of the trigger voltage, and the base-emitter voltage of the transistor Tr ₁ is a close circuit of the thyristor 12 When the potential is exceeded, thyristor 12 is triggered and conducts. Transistor Tr ₁ conducts because the base current is supplied,
The load 3 is driven. [Problems to be Solved by the Invention] However, each of these two prior arts has the following problems. First the first technique (FIG. 2 reference) of the above problem, a voltage drop occurs by the resistance R ₉ for inrush current limiting at power, constant voltage composed of MOS · FET1 and a Zener diode ZD ₁ It is necessary to increase the output voltage of the circuit by the drop. The constant voltage circuit has a characteristic that when the supplied power supply voltage falls below a certain voltage, the output voltage starts to decrease rapidly. Therefore, connecting a power supply voltage as large as possible is a necessary condition for an accurate detection operation. However, in practice, a low-voltage AC power supply often has to be used, and in this case, a problem occurs. For example, assuming that a commonly used 5 mA / 200 V mini chair relay is used for the load 3 and the supply voltage to the detection circuit 10 is about 7 V, the load 3 is driven unless the inrush current is 5 mA or less. Therefore, the resistance value of the resistor R ₉ must be about 1.4KΩ more. Since the current consumption of the general detecting circuit 10 is about 1 mA, the voltage drop of the resistor R ₉ is about 1.4V. In this case, if a low voltage AC power supply such as 24V is used, 1.4V
Is not negligible. Further, the first technique has the following problems. Which in each AC 2-wire proximity switch because there are variations in threshold voltage of the MOS · FET1, not must respectively so selected Zener voltage of the Zener diode ZD ₁ corresponding to the threshold voltage value, mass The problem is that it is not suitable for realization. The second technique (see FIG. 3) is being eliminated a problem that difficulty in this mass production of the first technique, the inrush current at power-on is rapid charging flows into the smoothing capacitor C ₁ However, there is a problem that no countermeasures are taken against driving the load 3. Therefore, similarly to the problem with the first technique, a malfunction occurs when a small current drive type is used for the load 3. The present invention has been made in view of the above problems,
AC2 that reduces leakage current and residual voltage, allows mass production, and is less likely to malfunction at power-on
It is intended to provide a wire type non-contact switch. [Means for Solving the Problems] Specific means for solving the above problems and achieving this object are an AC power supply connected in series to a load via a constant voltage circuit and a full-wave rectifier circuit. A detection circuit that outputs a detection signal according to proximity or separation of a detection object to be connected, a switching element that controls a load according to the detection signal, and a smoothing capacitor that supplies a voltage to the detection circuit when the load is driven And a current detecting element for detecting a charging current to the smoothing capacitor connected in series with the smoothing capacitor, wherein the constant voltage circuit is a MOS-FET (Metal Oxide Sequential).
miconductor ・ Field Effect Transistor) and this MO
A Zener diode connected to the source of the S-FET, connected to the gate of the MOS-FET, and controlling the gate voltage of the MOS-FET by the output of the current sensing element to reduce the charging current. A feedback circuit connected in parallel with the current detecting element for controlling,
The charging current to the smoothing capacitor when the detection signal is not output is kept constant. [Operation] Since the present invention employs the above-described means, the following operation is provided. First, when the power is turned on, an inrush current is generated and tries to flow into the smoothing capacitor via the constant voltage circuit.However, the inrush current is limited to a constant current value by the current detecting element and the feedback circuit, and the No quick charge is made. Next, when the detection circuit outputs a detection signal, the anode voltage of the Zener diode rises, so that the switching element is triggered and conducts, so that the load is driven. Since the feedback circuit holds the gate voltage of the MOS-FET at or above the threshold voltage, a constant current is supplied to the switching element via the FET, and the load is driven normally.
In this case, a voltage is supplied to the detection circuit from the smoothing capacitor, and the normal detection operation function is maintained. [Embodiment] The present invention will be described in detail below with reference to one embodiment. The same parts as those in the conventional example are denoted by the same reference numerals, and description thereof will be simplified. As shown in FIG. 1, the output terminals 5 and 6, the diode bridge circuit 8, the components of the smoothing capacitor C ₁ is the same as the conventional example. The positive side of the diode bridge circuit 8, a constant voltage circuit comprising a Zener diode ZD ₄ which is connected to the MOS · FET 14 and the source of the enhancement characteristics are connected. With the resistance R ₁₀ of the large resistance value is connected to the gate of the FET 14, the transistor Tr ₆ and Tr ₇ are connected in series. The output signal of the detection circuit 15 is adapted to be transmitted to the base of the transistor Tr _7. The FET14 source via a diode D _4, resistor R ₁₁ and a smoothing capacitor C ₁ is connected in series a current sensing element. The transistor Tr ₄ is a feedback circuit in parallel is connected to the resistor R _11, the collector of the transistor Tr ₄ is connected to the gate of the FET 14. Further, the transistor Tr ₅ the resistor R ₁₁ is shunt circuit
Are also connected in parallel, the base of the transistor Tr ₅ is connected to the detecting circuit 15 through the LED ₁ and the resistor R ₁₄ is an operation indicator. The Zener diode ZD ₄ of the constant voltage circuit, a diode D ₅ and the resistor R ₁₃ are connected in series. In parallel with these, the resistance R ₁₂ is connected thyristors 16 and overcurrent detection element is a switching element. The collector of the transistor Tr ₄ is connected to the thyristor 17 is a current switching element. Thyristor 17 through a resistor R _15, is connected to a connection point of the thyristor 16 and the resistor R _12. The resistance value of the resistor R ₁₁ is 200
Omega, resistance of the resistor R ₁₀ is 5 M [Omega. The operation of this circuit having such a configuration will be described below. First, when the power is turned on, the inrush current
Via the 14 tries to flow into the smoothing capacitor C _1. However, since the resistance value of the resistor R ₁₁ as described above is a 200 [Omega,
0.6V voltage drop occurs across the resistor R ₁₁ 3mA current flows. By this voltage drop is the transistor Tr ₄ is biased a feedback circuit conductive, functions to hold the charging current to the smoothing capacitor C ₁ of FET14 constant. Smoothing capacitor C ₁ will be charged by receiving supply of the charging current. At this time the detection circuit 15 does not output the detection signal, the output signal of the detection circuit 15, the transistor Tr ₇ becomes HIGH is biased conductive. Also the transistor Tr ₆ conducts this conduction, FET 14 is supplied to the detecting circuit 15 and a smoothing capacitor C ₁ of the constant voltage. Next, an operation in the case where the detection circuit 15 outputs a detection signal according to proximity or separation of the detection target will be described.
When the detection signal is output, the output signal of the detection circuit 15 becomes LOW.
Flip to Therefore, transistor Tr ₇ is shut off,
Transistor Tr ₆ is also blocked. The anode voltage of the Zener diode ZD ₄ is raised by the blocking thyristor 1
6 is triggered to conduct. Therefore, the current supplied through the diode bridge circuit 8 flows through the FET 14 and the thyristor 16, so that the load (see the drawing) is driven to notify that the load has been detected. The gate of this case FET 14, the voltage of the smoothing capacitor C ₁ is the transistor Tr ₄
Via the base collector. Therefore FE
The gate voltage of T14 is maintained at or above the threshold voltage, and supplies a current during detection signal output to the thyristor 26 to maintain normal operation. On the other hand, the transistor Tr ₅ by the output of the detection signal of the detection circuit 15 is biased to conduct. Due to this conduction, the LED ₁ emits light to clearly indicate to the outside that the detection signal is being output. Since the charging current by the conduction of the transistor Tr ₅ flows rapidly to the smoothing capacitor C _1, the capacitor C ₁ is completed to charge in a very short time. Therefore, without insufficient supply voltage to the detection circuit 15 during discharge of the capacitor C ₁ at the time of detection signal output, the normal detection operation function is maintained. During discharge therewith, the discharge current is supplied to the LED ₁ through the collector-base of the transistor Tr _5. Therefore, during the output of the detection signal, the LED ₁ emits light to clearly indicate that the detection is being performed. In this case, a substantially constant current is supplied to the LED ₁ and the LED ₁ always emits light with a constant brightness.
No problem brightness of D ₁ varies. Next, the overcurrent protection function will be described. If an overcurrent becomes short-circuited by erroneous connection or accidents load during the detection signal output from flowing into the circuit, the resistor R ₁₂ is an overcurrent detection element connected in series to the thyristor 16 detects an overcurrent. Thus the voltage across the resistor R ₁₂ is increased, the thyristor 17 is triggered to conduct. Voltage to the gate of FET 14 which has been supplied from the transistor Tr ₄ This conduction is short, FET 14 is blocked. Current resistance value of the resistor R ₁₀ is flowing here for quite large and 5MΩ as described above 10 ^-1
mA or less, no problem. Therefore, the overcurrent is cut off instantaneously, and the protection of the FET 14 and the thyristor 16 is achieved. MOS ・ FET14 which can increase the input impedance of the gate
Because the uses the constant voltage circuit, can be selected large resistance value to the resistor R ₁₀ in this embodiment. Therefore, the leakage current when the detection signal is not output is extremely reduced. [Effects of the Invention] As is apparent from the above description, the present invention provides a method for controlling the proximity or separation of a detection target connected to an AC power supply connected in series to a load via a constant voltage circuit and a full-wave rectifier circuit. A detection circuit that outputs a detection signal, a switching element that controls a load in accordance with the detection signal, a smoothing capacitor that supplies a voltage to the detection circuit when the load is driven, and a series connection with the smoothing capacitor. A current detecting element for detecting a charging current to the smoothing capacitor,
In an AC two-wire contactless switch having a switch, the constant voltage circuit is a MOS / FET (Metal Oxide Semiconductor / Field).
Effect Transistor) and a Zener diode connected to the source of the MOSFET, connected to the gate of the MOSFET, and controlling the gate voltage of the MOSFET by the output of the current sensing element. Since the feedback circuit connected in parallel with the current detecting element for controlling the charging current keeps the charging current to the smoothing capacitor constant when the detection signal is not output. Even if a load driven by a small current is connected, no malfunction occurs. Further, since the resistance value of the current detecting element can be reduced, the output voltage of the constant voltage circuit can be reduced, and no malfunction occurs even when a low-voltage AC power supply is used. Further, since the inrush current at the time of turning on the power is limited to a constant current value by the feedback circuit and the current detecting element, no malfunction occurs at the time of turning on the power even when a load driven by a small current is connected. Furthermore, since the MOSFET is used in the constant voltage circuit, the impedance at the time of conduction is small, the residual voltage can be reduced, and the device can be suitable for mass production.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of one embodiment of an AC two-wire contactless switch according to the present invention, and FIGS. 2 and 3 are circuit diagrams of a conventional example. 14… MOS / FET, 15… Detector circuit, 16… Thyristor (switching element), 17… Thyristor (current switching element), C ₁ …… Smoothing capacitor, R ₁₁ …… Resistance (current detecting element) , ZD ₄ … Zener diode, Tr ₄ … Transistor (feedback circuit), Tr ₅ … Transistor (shunt circuit), LED ₁ … Light-emitting element (operation indicator light).

Claims (1)

(57) [Claims] A detection circuit that is connected to an AC power supply connected in series to the load via a constant voltage circuit and a full-wave rectifier circuit and outputs a detection signal when the object to be detected approaches or separates from the object, and controls the load according to the detection signal A switching element that supplies a voltage to the detection circuit when the load is driven; and a current detection element that detects a charging current to the smoothing capacitor connected in series with the smoothing capacitor. In the two-wire contactless switch, the constant voltage circuit includes a metal oxide semiconductor (MOS) FET having a resistor connected between a drain and a gate.
ect Transistor), a Zener diode having one end connected to the source of the MOS-FET and the other end connected to the control terminal of the first switch means, and the gate of the MOS-FET and the detection signal are input to the control terminal. The first switch means connected to the second switch means, the control terminal of the switching element is connected to the other end of the Zener diode, and connected in parallel with the current sensing element. The output from the current sensing element is output to the gate of the MOSFET
1. An AC two-wire contactless switch having a feedback circuit for controlling the gate voltage of the MOS-FET. A shunt circuit connected in parallel with the current detecting element, wherein when a detection signal is output via the shunt circuit, a drive current is supplied to a light emitting element serving as an operation indicator lamp when the smoothing capacitor is charged. 2. The AC two-wire contactless switch according to claim 1, wherein a discharge current of the smoothing capacitor is supplied to the light emitting element as a drive current when the smoothing capacitor is discharged. 3. An AC two-wire contactless switch according to claim 1, wherein said MOS-FET has enhancement characteristics.