JPS612411A - Photoisolation circuit - Google Patents

Abstract

PURPOSE:To prevent the titled circuit from misconnection and to simplify the device by providing an output circuit with a restart type monostable multivibrator and a holding time setting circuit for setting up the holding time of said multivibrator. CONSTITUTION:The output of an AND circuit 12 is inputted to the restart type monostable multivibrator (hereinafter referred to as a multivibrator) 13. The output pulse width of the multivibrator 13 is obtained by setting up the time required for the inversion of an inverted output to the original state to a time between a half cycle and one cycle of the input AC signal. The output of the multivibrator 13 and a part of the input of a phase inverter 11 are inputted to an NAND circuit 15. In any case that a DC or AC input signal is inputted, the output of said NAND circuit 15 is kept at ON until the input signal is interrupted. If the voltage of the input signal is higher than the Zenner voltage of a constant voltage diode, the circuit can be used at a high voltage only by increasing the number of serial constant current diodes.

Description

Detailed Description of the Invention (Objective) The present invention relates to a photo-isolation circuit that always outputs a DC output signal regardless of whether the input signal is DC or AC. It is an i-ode isolation circuit that can input from AC to commercial frequency, and in the case of DC, regardless of the input polarity, and operates with the input signal and output signal electrically isolated.

(Prior art) In general, when inputting drowsiness signals from sensors, control devices, power devices, etc. used in the field to computers, OA equipment, FA equipment, etc., noise from the input circuits and people in each device Equipment troubles are likely to occur due to stray currents caused by potential differences due to differences in output standards, so to prevent such troubles, input coupling circuits using opto-isolated elements and solid-state relays (S8R) are often used. However, the types of output and input signals of each device vary depending on whether it is direct current or alternating current and the magnitude of the voltage, so the input circuit of each device is also prepared according to the standards mentioned above. There must be. This not only results in increased cost and complexity of the device, but also causes troubles due to incorrect connections.

(Summary) The present invention was made to solve these problems, and can be used for input signals with a wide allowable voltage range, regardless of whether the input signal is AC or DC, and regardless of the polarity in the case of DC. In a photo-isolation circuit that provides an input circuit and electrically isolates input signals and output signals, outputs a constant current at a constant voltage for an input signal within a constant voltage range with direct current or alternating current below the commercial frequency. a photocoupler that outputs an output signal that is electrically isolated from the output signal of this input circuit; and a photocoupler that outputs an output signal that is electrically isolated from the output signal of this input circuit; The output circuit also includes an output circuit that outputs a DC output that turns ON or OFF in synchronization with the ON or OFF of this human input signal, and the input circuit is provided with a full-wave rectifier, a constant voltage diode, and a constant current diode, and the output circuit is provided with a full-wave rectifier, a constant voltage diode, and a constant current diode. A restart type monostable multivibration break and a hold time setting circuit for setting the hold time of this restart type monostable multipipulator are provided.
The present invention provides a photo-isolation circuit with zt characteristics.

This will be explained in detail below with reference to the drawings.

FIG. 1 is a connection diagram of the main parts of the photo isolation circuit of the present invention. The 0 circuit is roughly divided into an input circuit, a photo isolation circuit, and an output circuit 3. In the input circuit/, when the input signal is input from the input terminal, it is a full-wave rectifier! The rectified voltage is sent to the constant voltage diode B. This full wave rectifier! Therefore, in the case of DC input, the positive side is sent to constant voltage diode 4, regardless of the input polarity.If it is AC input, the pulsating current of full wave rectification is sent to constant voltage diode B. Since this voltage regulator diode is selected to meet the required voltage standard, it will not conduct when the input signal voltage is less than this standard value, and will conduct only when it is higher than this standard value. Output. This output is maintained at a constant output current by a constant current diode 2 connected in series with the constant voltage diode B.

The number of constant current diodes 7 to be connected in series may be selected depending on the voltage of the input signal input to this circuit. In this embodiment, there are three, and the upper limit of the input signal voltage is set to 3001. r is a protection resistance of the constant current diode.

In such a circuit, when the input signal is DC, the input signal is sent to the constant current diode 7 only when the voltage is equal to or higher than the Zener voltage of the constant voltage diode ≦ 0. If the input signal is AC, the input signal is sent to the constant current diode 7. The current becomes a pulsating current, and the waveform in which the portion below the Zener voltage of the constant voltage diode B is cut is sent to the constant current diode 7. The required number of constant current diodes 7 are connected in series according to the input voltage, and in this embodiment, three are used, and the maximum input voltage is 3θθV. The input signal, which is cut and further suppressed to below a constant current by the constant current diode 2, is sent to the photodiode of the next photoconverter and converted into an optical signal. This optical signal is input to a nearby phototransistor IO and changes this phototransistor IO from a non-conducting state to a conducting state. In other words, when there is a DC input signal, the phototransistor 10 is conductive, and when there is no DC input signal, the phototransistor 10 is conductive. is non-conducting,
When there is an AC input signal, it repeats periodic changes of non-conducting when the instantaneous value of the input signal is less than the Zener voltage and conducting when it is above the Zener voltage, and non-conducting when there is no input signal. The first diagram is a waveform diagram showing this state. A in the same figure
is an AC input signal, B is a full-wave rectified waveform, and OC, which is the input waveform of constant voltage diode B, is the input waveform of constant current diode 7.
In the output current waveform, the part of the input waveform whose instantaneous value is less than the zener voltage of the constant voltage diode near θ is cut off, and the pulse signal O is further suppressed to a constant current or less by the constant current diode. is input to the photodiode of the photodetector, the photodiode emits light in accordance with this, and the phototransistor 10 that receives this light repeats conduction and non-conduction. In the case of conduction, the collector potential of phototransistor io (point D)
is the ground potential, that is, the θ potential, and D in the case of non-conduction
The potential at the point is equal to the power supply potential Vaa, and is in an ON state.

This waveform is an inverted version of the waveform at the 0 point.

A part of the waveform at point D is the output circuit 30 phase inverter/
It is inverted again at / (IC point) and becomes the same waveform as the 0 point, which is input to the AND circuit 12 of the output circuit 3. Since the other input of this AND circuit is the power supply potential VCC, it is always in an ON state. Therefore, the output of the AND circuit 12 is E
The state is the same as the waveform of the point. The output of this AND circuit t is inputted to a restart type monostable multipipulator (hereinafter referred to as multipipulator) /J provided next. The output pulse width of the multipipulator 13 is determined by the hold time setting circuit 1avc, and the time required for the inverted output to invert back to its original state is determined by the half cycle of the input AC signal.
Set it to the time between cycles. For example, input AC signal! In the case of θH2, it is set to 17 to 72 m8 for 10 m5 for half the cycle.

By setting K in this way, the rise of the output voltage of the constant voltage diode B in the first half cycle turns the waveform at the point E into an ON state, which causes the multipipulator 13 to turn on.
becomes the trigger pulse of the multi-pipetrator 13.
The output of is inverted. Since the time during which this output is inverted is set to a necessary time by the hold time setting circuit A, the waveform of the input AC signal finishes the first half cycle and enters the second half cycle. This is the time when the inverted state of the output of the multipipulator/3 is restored, but at this point, the trigger pulse has been generated by the Cth half cycle, so the inverted state of the output of the multipiperator/3 is maintained. Ru. As long as the input AC signal continues in this way, the inverted state of the output of the multipipulator 13 continues, but the last half cycle when the input AC signal is cut off! At the end of the inverted state of the output of the multipipulator 13, this output returns to its original state (FIG. F).

The output of this multipipulator 13 and the phase inverter/
If the other part of the input of l (point D) is input to the NAND circuit /j, and the input signal is either DC or AC, the NAND circuit /S will continue to operate until the input signal is disconnected. The output remains ON.

When the input signal is DC, even if the connected polarity is positive or negative, the full-wave rectifier J keeps the voltage regulator diode t in operation when the input voltage is higher than the Zener diode of the voltage regulator diode. Therefore, as long as the DC input signal continues, point D remains in the OFF state, and the NAND circuit/S
The output of remains ON.

This holding time is reversed immediately after the input signal disappears and returns to the unmanned state. However, the time from when the input signal turns ON until it turns OFF is the holding time of the multipipulator 13 (for example, //y/ If it is shorter than 2 nu+ ), it is reversed and returns to the unmanned state after //~1 mB after the input signal disappears.

As described above, the photo-isolation circuit of the present invention is not only electrically isolated between the input and output, but also
There is no problem whether the input signal is direct current or alternating current below the commercial frequency. Furthermore, if the voltage of the input signal is higher than the Zener voltage of the constant voltage diode, it can be used even in the case of high voltage by simply increasing the number of constant current diodes in series, and can also be used in the case of a wide range of frequencies and voltage deviations. Furthermore, if the input signal is a direct current, the polarity of the connection can be either, so there is no erroneous connection, and circuit standardization can be implemented, which has extremely great practical effects.

[Brief explanation of drawings]

FIG. 1 is a connection diagram of the main parts of the photo-isolation circuit of the present invention, and FIG. 2 is a waveform diagram of each part on the circuit.

Claims (1)

[Claims] In a photo-isolation circuit that electrically isolates an input signal and an output signal, an input circuit that limits an input signal within a certain voltage range with DC or AC below the commercial frequency to an output signal of a constant voltage and constant current, and this input circuit. A photocoupler that outputs an output signal that is electrically isolated from the output signal of the circuit, and the output signal of this photocoupler synchronizes the ON or OFF of this input signal regardless of whether the input signal of the input circuit is DC or AC. The input circuit is equipped with a full-wave rectifier, a constant voltage diode, and a constant current diode, and the output circuit includes a restart type monostable multipipulator and this output circuit. A photo isolation circuit comprising a hold time setting circuit for setting a hold time of a restart type monostable multipipulator.