JPS61264916A - Surge absorbing circuit - Google Patents

Abstract

PURPOSE:To protect a logic circuit by providing a capacitor between a signal line and an earth of the logic circuit and connecting the 2nd diode to the earth so as to allow the circuit to show a low impedance to a negative surge voltage. CONSTITUTION:A resistor 24 is arranged to discharge an electric charge of a capacitor 23 and a resistor 28 is arranged to limit a current flowing to a contact 4 by the discharge of the capacitor 23 when the contact 4 is closed. When a positive surge is fed to an input terminal 6 of a device 27, since the diode 22 exists in reverse polarity to the positive surge, the surge is absorbed by the capacitor 23 and the surge voltage is divided by the resistor 25 so as to protect the logic circuit 8. When a negative surge is fed to the input terminal 6, the surge path is short-circuited by the diode 21 and the surge is absorbed and blocked by the capacitor 23 and the resistor 25 to protect the logic circuit 8.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a surge absorption circuit for protecting logic circuits and the like from surges.

Conventional Technology In recent years, the wave of informatization has expanded into various fields, and management systems using various sensors have already begun to spread. If the signal line that transmits the signal from the valley sensor to the logic circuit of the control device is long and there is a high possibility that a surge will be applied, the logic circuit and the photo coupler that protects it should be protected from damage as shown in Figure 2. As shown in the figure, ZN)t and diodes are often used as surge absorbing elements.

An example of the conventional method will be described below with reference to FIG.

In FIG. 2, when the sensor 1 for heat, gas, etc. responds, the sensor side device 2 closes the contact 4 in order to output the information to other devices 3. The closed state of the contact 4 is passed as an output signal to the input terminals 6, 6' of the device 3 via the transmission line 5. That is, when the contact 4 is closed, a current flows from the power supply E1 of the device 3 to the light emitting diode of the photocoupler 7, and the logic circuit input terminal 12 becomes the LOVV level, and when the contact 4 is open, the light emitting diode of the photocoupler 7 flows. Since no current flows through the input terminal 12 of the logic circuit 80, f(f
The state of the contact point can be grasped by the logic circuit 8 based on the state of the sensor 1 at the gh level.

Under such usage conditions, when the transmission line 6 is long and a surge is applied to the input terminals 6 and 6', the ZNR 9 and the resistor 10 absorb and block the surge, and the diode 11 prevents the photocoupler 7 from emitting light. Protects against diode reverse voltage.

Furthermore, the logic circuit 8 is protected by a photocoupler 7.

Problems to be Solved by the Invention However, the conventional configuration shown in FIG. ing. In addition, while the power supply E2 for driving the logic circuit is normally 6 volts, the power supply E1 for driving the light emitting diode generally requires a power supply of 5 volts or more due to the surge voltage blocking resistor 1o.

In addition, the input terminals 6, 6', ZNRg, resistor 1o, diode 11, and photocoupler 7 constitute the above-mentioned surge protection circuit, but as the number of contacts 4 increases, this protection circuit becomes The number of protection circuits also increases, and the power supply E1 is required to have a power supply capacity proportional to the number of protection circuits. Therefore, when the number of protection circuits increases, the power source E1 has a disadvantage in that the influence on the device 3 in terms of shape and cost increases.

The present invention is a surge absorption circuit for protecting the input signal circuit of equipment in which the input signal speed is extremely slow and the applied surge voltage is low and is applied infrequently.The present invention solves the problems of the conventional example. It is something to be solved.

Means for Solving the Problems To achieve this objective, the surge absorption circuit of the present invention comprises:
It protects the logic circuit by consisting of a diode, capacitor, and resistor without using a photocoupler or ZNR.

Operation The present invention uses the above-described configuration as one power supply circuit for driving the logic circuit, thereby reducing the size of the power supply circuit and protecting the logic circuit.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings. FIG. 1 shows a surge absorption circuit according to an embodiment of the present invention. In FIG. The input terminal 12 of the circuit is the same as the conventional example shown in FIG.

When contact 4 is closed, resistor 26 and contact a of resistor 26
becomes LOW level and the logic circuit 8 input terminal 12 becomes LOW.
If contact 4 is open, contact a becomes high level and input terminal 12 of logic circuit 80 goes high.
Resistors 24, 25, and 26 are set so that the level is high. The resistor 24 is arranged to discharge the charge of the capacitor 23. Resistor 28 is arranged to limit the current flowing through contact 4 due to discharge of capacitor 23 when contact 4 is closed.

When a positive surge is applied to the input terminal 6 of the device 27, the diode 2 is connected in the opposite direction to this positive surge.
2, the logic circuit 8 can be protected by being absorbed by the capacitor 23 and divided by the resistor 25.

When a negative polarity surge is applied to the input terminal 6, it is short-circuited to the ground side by the diode 21, and is absorbed and blocked by the capacitor 23 and the resistor 25, so that the logic circuit 8 can be protected.

With this configuration, the same power source as the power source for driving the logic circuit 8 can be used, which eliminates the need to prepare multiple power supply circuits, which is a drawback of the conventional example, and The resistor 26, diode 22, resistor 28 from the power supply E2 for detecting the LoW level and High level at The impact on shape and price is extremely small.

Effects of the Invention As described above, according to the present invention, by removing ZhR and using diodes, resistors, and capacitors, a low-voltage power supply circuit can be used, which reduces the impact on the price and shape of equipment in the power supply circuit section. Since the power supply capacity is significantly reduced and the change in power supply capacity is much smaller compared to conventional ones, it is easy to share the same power supply circuit regardless of the number of circuits to be protected, and the shape of the equipment can be reduced. Sharing is also facilitated.

[Brief explanation of the drawing]

Figure g1 is a circuit diagram of a surge absorption circuit according to an embodiment of the invention, and Figure 2 is a circuit diagram of a conventional surge absorption circuit. 1...Sensor, 2...Sensor side equipment,
4...Contact, 6...Transmission line, 6,6',
12...Input terminal, 8...Logic circuit,
21.22...Diode, 23...
Capacitor, 24-26.28... Resistor, 27
······device. Name of agent: Patent attorney Toshio Nakao and one other person
...Sensor 2...1 sensor E section 21, 22...Die 4-de 23...Conductor 24, . 25.26.2,9. ,,Jshi4927,・
·device

Claims (1)

[Claims] In order to protect the logic circuit from surges caused by induction, etc., a first diode is placed so that it has a high impedance against positive surge voltage, and a capacitor is connected to the signal of the logic circuit to absorb the surge voltage. A surge absorption circuit that is provided between the line and the ground and has a second diode connected to the ground side so as to have a low impedance against surge voltages of negative polarity.