JPS6165512A - Photocoupler - Google Patents

Abstract

PURPOSE:To prevent chattering of an input signal or external noise from appearing in an output signal by detecting the lighting of a light emitting element to switch charge/discharge of an integration circuit and using a comparator having a hysteresis characteristic to obtain an output signal in response to a voltage change of the said integration circuit. CONSTITUTION:When a signal Vin is inputted between input terminals A and K, an infrared ray emitting diode 2 is lighted, a photodiode 3 receives this lighting and a current flows to the photodiode 3. On the other hand, when no signal VT is outputted to an output terminal 5d of a Schmitt trigger circuit 5, a charge/discharge switching circuit 6 is closed and a capacitor 9 is discharged through a constant current circuit 8 outputting a current nl1. Thus, the charge/discharge switching circuit 6 repeats switching in response to the chattering of the output signal VT of the Schmitt trigger circuit 5 and the capacitor 9 repeats charging/discharging. An output voltage of the switching circuit 11, that is, a voltage of one input terminal 10b of the comparator 10 inverts the output of the comparator 10 after a voltage at a non-inverting input terminal 10a drops to a voltage V1 or below.

Description

[Detailed description of the invention] Technical fields> The present invention relates to photocouplers.

<Prior Art> For example, in the input circuit of a programmable controller or the drive circuit of a switching element such as a gate turn-off circuit or a power transistor, a photocoupler is used which electrically insulates circuits and transmits signals using light.

As shown in Fig. 3, the conventional photocoupler has an input terminal A.
When a signal Vin is input between , , a current flows through the infrared light emitting element 21 , the infrared light emitting element 21 emits light, this light emission is received by the photodiode 22 , and a current flows through the photodiode 22 . The current signal flowing through the photodiode 22 is amplified by an amplifier 23, further converted by a Schmitt trigger circuit 24, and then amplified by an output amplifier 25 to obtain an output signal Vout.

FIG. 4 shows the waveforms of the input signal Vin and output signal Vout in the photocoupler described above, and when chattering a occurs in the input signal Vin, chattering also occurs in the output signal Vout. As described above, conventional photocouplers cannot remove chattering or external noise from the input signal, and the chattering or external noise appears in the output signal as is.

Therefore, there is a drawback that the input circuit of a programmable controller using this photocoupler or the drive circuit of a power switching element may malfunction.

<Object of the Invention> The present invention has been made in view of the above-mentioned circumstances, and its object is to provide a photocoupler that prevents input signal chattering and external noise from occurring in the output signal.

<Structure of the Invention> In the present invention, a photocoupler that electrically insulates circuits and transmits signals by light includes an integrating circuit and charging/discharging of the integrating circuit based on a signal corresponding to light emission from a light emitting element. The present invention is characterized in that it includes a switching means for performing switching, and a comparator for obtaining an output signal according to a voltage change of the integrating circuit.

<Example> An embodiment of the present invention will be described below.

FIG. 1 shows the circuit configuration of a photocoupler. Input terminal A,
An infrared light emitting diode 2 is connected between K and K.

A photodiode 3 that receives light emitted from this infrared light emitting diode 2 is connected between input terminals 4a and 4b of an amplifier 4,
A power terminal 4c of the amplifier 4 is connected to the terminal 13, and a ground terminal 4d of the amplifier 4 is connected to the terminal 14. The output terminal 4e of the amplifier 4 is connected to the input terminal 5a of the Schmitt trigger circuit 5, the power supply terminal 5b of the Schmitt trigger circuit 5 is connected to the terminal 13, the ground terminal 5c of the Schmitt trigger circuit 5 is connected to the terminal 14, An output terminal 5d of the Schmitt trigger circuit 5 is connected to an input terminal 6a of the charge/discharge switching circuit 6. A power source (not shown) is connected to the terminal 13, and the terminal 14 is grounded.

A constant current circuit 7 is connected between the output terminal 6b and the terminal 13 of the charge/discharge switching circuit 6, and the output terminal 6C of the charge/discharge switching circuit 6
A constant current circuit 8 is connected between the terminal 14 and the output terminal 6b of the charge/discharge switching circuit 6, and a capacitor 9 is connected between the output terminal 6b of the charge/discharge switching circuit 6 and the terminal 14.
is connected. The output terminal 6b of the charge/discharge switching circuit 6 is further connected to the +input terminal 10a of the comparator 10. The output of this comparator 10 has hysteresis characteristics. A switching circuit 11 is connected between one input terminal tab of the comparator 10 and the output terminal 10c.
0 power supply terminal 10d is connected to terminal 13, and earth terminal 10e of comparator 10 is connected to terminal 14. The output terminal 10 c of the comparator 10 is connected to the input terminal 12 a of the output amplifier 12 . Power terminal 12'b is connected to terminal 15. The power supply terminal 12c of the output amplifier 12 is connected to the terminal 13, and the output amplifier 12
The ground terminal 12d of is connected to the terminal 14.

The timing chart in FIG. 2 shows the operational state of the main parts of the circuit described above, and the operation of the circuit described above will be explained below with reference to FIG.

When a signal Vin is input between the input terminals A, the infrared light emitting diode 2 emits light, the photodiode 3 receives this light emission, and a current flows through the photodiode 3. This current signal is amplified by an amplifier 4, further waveform-converted by a Schmitt trigger circuit 5, and seven signals are outputted to an output terminal 5d of the Schmitt trigger circuit 5. Chattering a occurs when the input signal Vin rises, and chattering also appears in the output signal vT of the Schmitt trigger circuit 5 in accordance with this chattering a.

When the signal 7 is output to the output terminal 5d of the Schmitt trigger circuit 5, the charging/discharging switching circuit 6 is opened, and charging current 1 flows from the constant current circuit 7 to the capacitor 9. The charging voltage of the capacitor 9 is \^ux, where VO is the voltage at the start of charging, VALIXI, G is the capacitance of the capacitor 9, and t is the charging time.

On the other hand, the signal V is applied to the output terminal 5d of the Schmitt trigger circuit 5.
When 1- is no longer output, the charge/discharge switching circuit 6 closes.
The capacitor 9 is discharged through the constant current circuit 8 which outputs a current nll. The discharge current at this time is (n-1)[+
It is. The voltage VAUK at this time is: However, VO2 is the voltage VAIIX at the start of discharge, and t is the discharge time.

Therefore, in response to the chattering of the output signal of the Schmitt trigger circuit 5, the charge/discharge switching circuit 6 repeats opening and closing, and the capacitor 9 repeats charging and discharging. When the human input signal Vin rises, the voltage VAux gradually decreases due to chattering (.

The output voltage of the switching circuit 11, that is, the voltage of one input terminal tab of the comparator 10, is the voltage of the comparator 1 at this point.
The voltage VAux corresponds to the state of the output terminal 10C of the comparator 10.
The output of the comparator 10 is inverted for the first time when the voltage at a becomes equal to or lower than this voltage Vl. Then, the output signal Vout of the terminal 15 is “from the old ghll level” Low
At this time, the output voltage of the switching circuit 11 changes to the voltage v2, which is larger than the voltage ■1. In this way, after the input signal Vin rises, the voltage VALIX
When Vout reaches a certain level, the output signal Vout is inverted for the first time, and no chattering appears in the output signal Vout.

Next, when the signal Vin between the input terminals A and A disappears, the infrared light emitting diode 2 stops emitting light, and the infrared light emitting diode 2 stops emitting light, and the
No current will flow through. When the signal Vin falls, chattering a occurs, and in response to this chattering a, chattering also occurs at the output ①T of the Schmitt trigger circuit 5. Then, in response to the chattering of the signal V, the charge/discharge switching circuit 6 repeats opening and closing, the capacitor 9 repeats charging and discharging, and the voltage VAux gradually increases.

The output voltage of the switching circuit 11, that is, the voltage at one input terminal 10b of the comparator 10, is the voltage of the comparator 1 at this point.
0, the voltage ■2 corresponds to the state of the output terminal 10C, and when the voltage ■^ux becomes equal to or higher than this voltage ■2, the output of the comparator 10 is inverted for the first time, and the output signal Vo of the terminal 15
ut changes from the "low" level to the "old gh" level. At this time, the output voltage of the switching circuit 11 drops to voltage v1. In this way, when the voltage VAux reaches a certain level after the input signal Vin falls, the output signal V
out is inverted, and no chattering appears in the output signal Vout.

As described above, when a certain period of time has elapsed from the rise or fall of the input signal Vin, the state of the output signal vout is reversed. Therefore, the input signal Vi
The chattering of n and external noise do not appear in the output signal Vout. In addition, by creating a hysteresis characteristic by creating a difference between the voltage VAux when the output signal is inverted to the "'High" level and when it is inverted to the "0-" level, the output signal can be adjusted in response to minute fluctuations in the voltage VAux. Stabilize the signal Vout.

Note that, in this embodiment, the integrating circuit is configured using a constant current circuit and a capacitor, but an integrating circuit using a resistor and a capacitor may also be used. It is also possible to change the time constant by attaching an external capacitor and to make the output level of the connogrator variable.

<Effects of the Invention> As explained above, in the present invention, the light emission of the light emitting element is detected, the charging/discharging of the integrating circuit is switched, and the voltage change of the integrating circuit is controlled by the converter having hysteresis characteristics. Since the output signal is obtained according to the output signal, chattering of the input signal and external noise do not appear in the output signal, and a circuit using this output signal does not malfunction.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a timing chart of the embodiment of the present invention, FIG. 3 is a circuit diagram showing a conventional example, and FIG. 4 is a timing chart of the conventional example.

Claims (1)

[Claims] (1) A photocoupler that electrically insulates circuits and transmits signals by light, including an integrating circuit and a switching means for switching charging and discharging of the integrating circuit based on a signal corresponding to light emission from a light emitting element. , and a comparator that obtains an output signal according to a voltage change of the integrating circuit.