JPH0623005Y2 - Photo coupler circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is a photocoupler circuit suitable for an input circuit of a signal to an electronic circuit and the like. And a parallel resistor.

[Conventional technology]

As is well known, a photocoupler is very useful for isolating the input side and the output side from each other, especially when controlling a high voltage circuit by an electronic device such as a program controller. It is indispensable as an interface when a signal is fetched from the electronic circuit to the electronic circuit or a control signal is transmitted from the electronic circuit to the high voltage circuit. However, in a photocoupler used for an input circuit of a signal to an electronic circuit, when a noise voltage enters from a high voltage circuit, the light emitting element thereof emits light and an incorrect signal may be given to the electronic circuit. Therefore, a filter or a time constant circuit is inserted on the light receiving element side of the photocoupler so that a signal is not given to the electronic circuit as long as it is within a short time due to noise even if the light emitting element emits light by mistake. Has been done conventionally.

FIG. 5 shows such a conventional example. In the figure,
Reference numeral 1 denotes a photocoupler, which comprises a light emitting element 2 such as a light emitting diode and a light receiving element 3 such as a phototransistor. A photocoupler circuit 30 including this photocoupler 1 has a power supply 4 of a high voltage circuit at its left input terminal Ti. Switch the voltage V1 to 5
Upon receiving the intermittent input signal Si, the corresponding output signal So is given to the electronic circuit from the right output terminal To. The photo coupler circuit 30 includes a light emitting element side circuit and a light receiving element side circuit of the photo coupler 1. The former is composed of a series resistor 11 and a parallel resistor 12 for the light emitting element 2, and when the input signal Si is on, the voltage V1 is divided by the resistors 11 and 12 to cause the light emitting element 2 to emit light. The light receiving element side circuit is supplied with power from a power source V2 for an electronic circuit via a potential raising resistor 21, and the light receiving element 3 is connected in series with this raising resistor 21 as shown in the drawing. Discharge resistance in parallel with the light receiving element 3
A series circuit of 22 and a capacitor 23 is connected, and the voltage of the capacitor 23 is taken out as an output signal So via an inverter 24 that operates as a threshold.

When the input signal Si is off, the light emitting element 2 of the photocoupler 1 does not emit light, and therefore the light receiving element 3 is also off, so that the capacitor
23 is charged to the voltage V2 via the pull-up resistor 21 and the discharge resistor 22, and the inverter 24 receives this charge voltage and outputs an output signal.
So is off. When the input signal Si is turned on and the light receiving element 3 is turned on based on the light emission of the light emitting element 2, the capacitor 23 is discharged through the discharge resistor 22 and its voltage v2 becomes equal to or lower than the threshold value of the inverter 24. Output signal to So
Turns on.

Now, assuming that the noise N having a certain time width enters from the input terminal Ti and the light emitting element 3 emits light, the light receiving element 3 is turned on and the voltage v2 of the capacitor 23 decreases, but the value is the inverter 24. If the time until it becomes less than or equal to the threshold value of is set longer than the time width of the noise N, an erroneous signal due to noise does not occur in the output signal So. That is, in this conventional circuit, the discharge time constant determined by the discharge resistor 22 and the capacitor 23 in the light receiving element side circuit is set to be long with some margin with respect to the maximum time width that the noise N can have. , So that an erroneous signal due to noise does not occur in the output signal So. Of course, when the regular input signal Si having a time width longer than the noise time width is given, the photocoupler circuit 30 operates normally.

[Problems to be solved by the device]

However, this conventional photocoupler circuit has a problem that an erroneous signal is emitted when noise repeatedly enters. This will be described with reference to FIG.

FIG. 6 (a) shows a voltage waveform of noise penetrating into the nesting terminal Ti. In the figure, for simplification, it is assumed that a triangular wave noise voltage continuously invades. FIG. 3B shows the voltage v1 applied to the light emitting element 2 of the photocoupler 1 due to this noise voltage. This voltage v1 is obtained by dividing the noise voltage Vn by the two resistors 11 and 12, and originally has a similar waveform to the noise voltage Vn, but the value exceeds the light emission threshold Vt1 of the light emitting element 2. If so, it is clamped to this threshold value, so that it becomes a trapezoidal shape as shown. FIG. 6C shows the light emission L of the light emitting element 2, and as can be easily understood, the light L is turned on within the time corresponding to the flat portion above the voltage v1. In the figure, (b) shows the nesting voltage to the inverter 24 in the circuit on the light receiving element side, that is, the voltage of the capacitor
v2, and when the light L is on, it falls with the above-mentioned time constant,
It stands up when the light L is off. However, if noise repeatedly invades and the light emitting element 2 emits light repeatedly in response to this, the rise or recovery of the voltage v2 cannot catch up with it. The value gradually decreases with each emission as shown in the figure, and finally the threshold value of the inverter 24.
Since it falls below Vt2, an erroneous signal occurs in the output signal So at this point as shown in FIG.

As described above, the problem when the noise is repeated or continuously intrudes can be solved by increasing the recovery speed of the voltage v2 of the capacitor 23, that is, the time constant of its charging. Since it is determined by the product of the sum of the resistance values of 21 and the discharge resistance 22 and the capacitance value of the capacitor 23,
It is always greater than the discharge time constant. Of course, it is not impossible to make the charging time constant smaller than the discharging time constant by devising the circuit, but the magnitude relationship or ratio of these time constants depends on the chattering and bounce of the switch 5 on the input signal Si side ( It has a connection with measures against (repelling),
I am not allowed to choose too freely.

The present invention solves such a problem so that there is less risk of generating an erroneous signal even if noise is repeatedly introduced and a photo signal that can operate at a normal response speed to a regular input signal. The purpose is to obtain a coupler circuit.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present invention provides a series resistor and a parallel resistor for a light emitting element in a light emitting element side circuit of a photocoupler, and a discharge resistor connected in series with the light receiving element in a light receiving element side circuit of a photocapra. In a photocoupler circuit provided with a noise removing capacitor, a capacitor is connected in parallel to a parallel resistor for the light emitting element of the light emitting element side circuit, and noise in the noise which may enter from the outside to the light emitting element side of the photocoupler circuit. The time constant was selected so that the maximum value of the noise of the voltage applied to the parallel resistance within the time width with respect to the maximum product of the voltage and the time width is 1.5 times or less the light emission threshold of the light emitting element. Characterize.

[Action]

The present invention focuses on the fact that the time width of the noise voltage, which is the cause of the problem, is shorter than that of a regular signal, and if this property is used, noise can be distinguished from a regular signal and countermeasures can be taken. Rather than applying to the light receiving element side circuit that handles the digitalized signal through the photo coupler like
Rather, it was made paying attention to the fact that it is more advantageous to apply it to the light emitting element side circuit that handles analog signals, and as described above, connect a capacitor in parallel to the parallel resistance in the light emitting element side circuit. As a result, the light emission time of the light emitting element based on the noise voltage is shortened as compared with the conventional one or the light emission is eliminated to prevent an erroneous signal from occurring.

The operation of the above configuration will be described below with reference to FIGS. 1 and 2.

FIG. 1 shows a circuit on the side of the light emitting element 2 of the photocoupler 1 in the photocoupler circuit. As can be seen from the figure, the light emitting element 2 is provided with a series resistor 11 and a parallel resistor 12. 1 is the same as the conventional one, but according to the present invention, the capacitor 13 is connected in parallel to the parallel resistor 12. From the input terminal Ti, noise N having various waveforms such as triangular wave shape and rectangular shape as shown in the figure may enter. However, for the sake of simplification and in the following, the rectangular noise having the worst condition may enter. It is assumed that This waveform shows noise voltage V in Fig. 2 (a).
It is shown enlarged as n, and assuming that the capacitor 13 is not connected, this is represented by the resistance value Rs of the series resistor 11.
Voltage divided by the resistance value Rp of the parallel resistor 12 and Vd = Vn.Rp /
Since (Rs + Rp) is applied to the light emitting element and the value of the voltage Vd is larger than the light emitting threshold value Vt1 of the light emitting element, the light emitting element emits light over the time width Tn of noise. According to the present invention, when the capacitor 13 having the capacitance value C is connected in parallel with the parallel resistor 12, the voltage applied to the light emitting element 2 is increased.
As shown in the figure, the rising of v1 is delayed, and its time course is well known, and is represented by v1 = Vd (1-e- ^{t /} _τ ). However, τ is a time constant, and when the parallel resistance value of both resistors 11 and 12 is R, 1 / R = 1 / Rs + Rp with τ = C · R. When the voltage v1 rises to the light emission threshold value Vt1 of the light emitting element, the light emitting element causes light emission L as shown in FIG. 7B, but the light emission time TL is always shorter than the noise time width Tn. When the light emitting element emits light, the voltage v1 is almost clamped to the light emission threshold Vt1 as shown in the figure.

The higher the noise voltage Vn is, the faster the voltage applied to the light emitting element rises, and the longer the time width Tn is, the higher the maximum value that can be reached within the time width Tn is. Therefore, this maximum value is the voltage value and the time width of the noise. It is almost decided by the product of and. In order to shorten the light emission time TL of the light emitting element due to noise, the maximum value that can be taken within the time width Tn of the voltage v1 is set even if the time constant τ is increased and the product of the voltage and the time width is maximum. The light emission threshold Vt1 of the light emitting element should not be exceeded so much. Assuming that the maximum value of the voltage v1 occurs at the end of the time width Tn as in this example, this relationship is expressed by the coefficient K defined by K = (Vd / Vt1) (1-e- ^{rn /} _τ ). Therefore, the coefficient K should be set so as not to exceed 1 by selecting a large time constant τ. However, if the time constant τ is made too large, the ON operation speed of the photocoupler circuit will be slowed down, and therefore the coefficient K will be restricted by itself. Under this constraint, it is empirical to shorten the light emission time of the light emitting element due to noise as much as possible and effectively prevent the generation of an erroneous signal, but it is empirical that the time constant τ is set so that the coefficient K becomes 1.5 or less. It is desirable to select.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 3 and 4. FIG. 3 is a circuit diagram of an embodiment of the photocoupler circuit 30 according to the present invention.
Since the figure and the circuit on the light receiving element side are the same as those in FIG. 5 and corresponding parts are designated by the same reference numerals, the description thereof will be omitted at all. The operation will be described below with reference to FIG. 4 in the case where a continuous noise N having a triangular waveform as shown in the figure enters from the input terminal Ti.

The noise voltage Vn is shown in FIG. 4 (a) with the same waveform as in FIG. 6 above, and the waveform of the voltage v2 applied to the light emitting element 2 is shown in FIG. 4 (b). Explaining the noise peak at the left end of the figure, when the noise voltage Vn rises in the positive direction from time t0, the voltage V1 also rises accordingly, but its rise is gentler than before due to the capacitor 13, and its maximum value is a triangular wave. In the case, it is near the end of the time width Tn of noise. However, if the noise voltage is high as in this example, the voltage v1 reaches the light emission threshold value Vt1 of the light emitting element 2 by the time it reaches this maximum value, and from this time t1 as shown in FIG. Happens. Therefore, after this time t1, the voltage is
v1 is clamped to the light emission threshold Vt1. When the light emitting element 2 emits light, its forward resistance is connected in parallel to the parallel resistance 12, and the noise voltage is divided by the series resistance 11 and the combined resistance of the forward resistance and the parallel resistance 12, and the light emitting element is thus divided. Therefore, the light emission L is maintained while the divided voltage exceeds the light emission threshold value Vt1 of the light emitting element.
This limit value at which the noise voltage can maintain the light emission is shown by the sustain voltage Vh in FIG. 9A, and the light emission L stops at the time t2 when the noise voltage Vn drops to the sustain voltage Vh.
At this light emission stop time t2, the capacitor 13 has the light emission threshold Vt1.
However, the voltage v2 decays fairly rapidly as shown in FIG. 6 (d) because it is discharged by the parallel resistance 12 having a low resistance value.

As long as the noise voltage Vn and the time width Tn are large, the light emission L is generated for each positive peak of the noise as shown in FIG.
When the noise voltage and the time width are small as shown by the peak at the right end of (a), the voltage v1 applied to the light-emitting element accordingly rises from time t3, but its maximum value is The light emission threshold Vt1 has not been reached, so no light emission occurs. Further, as can be seen by comparing with FIG. 6 corresponding to the same noise voltage waveform, in the photocoupler circuit according to the present invention, each light emission time TL becomes much shorter than before even if the light emission L occurs. FIG. 7D shows how the input voltage v2 to the inverter 24 in the light receiving element 3 side circuit changes with the light emission L.
Since each light emission time TL is shorter than before, the voltage v2 once falls during this period as shown in the figure, but recovers to a voltage close to the power supply voltage v2 until the next light emission occurs. For this reason, in the circuit of the present invention, even if noise continuously intrudes and the light emission L is repeatedly generated as in this example, the rising of the voltage v2 is gradually accumulated as in the conventional case, and its value is increased. Does not fall below the operating threshold value Vt2 of the inverter 24. Therefore, the output signal S
No false signal is generated at o.

As can be seen from the embodiments described above, in the light emitting element side circuit of the photocoupler according to the present invention, the capacitor 13
The operating time constant created by the capacitance of is selected according to the time width of the noise coming from the input terminal. On the other hand, the operation time constant related to the capacitor 23 of the light receiving element side circuit is selected according to the operation speed required for the photocoupler circuit 30 as described above. In other words, in the present invention, noise countermeasures can be applied to the light emitting element side circuit independently of the operation speed of the photocoupler circuit. Therefore, even if the present invention is implemented, the operation characteristics of the photocoupler circuit are not affected. Is not affected by it.

Although the input signal Si is generated from the DC power supply 4 in the above embodiments, the present invention can be realized by appropriately adding a rectifier or the like to the light emitting element side circuit even if the power supply 4 is an AC power supply. The present invention can be implemented in various ways without being limited to the illustrated embodiment.

[Effect of device]

As described above, in the present invention, the series resistance and the parallel resistance with respect to the light emitting element are provided in the light emitting element side circuit of the photocoupler, and the discharge resistance and the noise connected in series with the light receiving element are provided in the light receiving element side circuit of the photocoupler. In a photocoupler circuit provided with a removing capacitor, a capacitor is connected in parallel to a parallel resistor for the light emitting element of the light emitting element side circuit, and a voltage in noise that may enter from the outside to the light emitting element side of the photocoupler circuit. By selecting the time constant so that the maximum value of the noise of the voltage applied to the parallel resistance within the time width with respect to the maximum product of the time width is 1.5 times or less of the light emission threshold of the light emitting element, the noise In addition to the noise removal capacitor on the light-receiving element side and the light-receiving element side circuit, measures against erroneous signals due to intrusion of The time for light emission can be shortened, the adverse effect on the circuit on the light receiving element side is significantly reduced, and the generation of false signals due to noise is virtually eliminated, and this false signal countermeasure adds a capacitor to the circuit on the light emitting element side. Therefore, the characteristics such as the operating speed of the photo coupler circuit set on the light receiving element side with respect to a normal signal are not affected by the implementation of the present invention, and the characteristics required or desired for the photo coupler circuit are not required. Can be easily held. Furthermore, only one capacitor needs to be added to the conventional circuit for implementing the present invention, and the operation reliability of the photocoupler circuit can be significantly improved with a slight loss.

The photocoupler circuit according to the present invention having such features is particularly suitable for an input circuit of a signal to an electronic circuit as described above,
It is very effective and useful in reducing malfunctions of electronic circuits due to noise.

[Brief description of drawings]

1 to 4 relate to the present invention, FIG. 1 is a circuit diagram of a main part of a photocoupler circuit according to the present invention, FIG. 2 is a waveform diagram for explaining its operation, and FIG. 3 is an implementation of the present invention. An example circuit diagram and FIG. 4 are waveform diagrams of the main signals. FIG. 5 and subsequent figures relate to the conventional technique, FIG. 5 is a circuit diagram of a conventional photocoupler circuit, and FIG. 6 is a waveform diagram of main signals thereof. In the figure, 1: photo coupler, 2: light emitting element, 3: light receiving element, 4:
Input side power supply, 5: switch, 11: series resistance, 12: parallel resistance, 13: capacitor, 21: potential raising resistance, 22: discharge resistance, 23: capacitor, 24: inverter, C: capacitance value of capacitor 13, L : Light emission, N: noise, Si:
Input signal, So: Output signal, Ti: Input terminal, Tn: Noise time width, To: Output terminal, TL: Light emission time, t: Time, t0 ~
t3: time t0, Vd: divided voltage value of noise voltage, Vh: sustain voltage,
Vn: noise voltage, Vt1: light emission threshold of light emitting element, Vt2:
Inverter operating threshold, V1: Input signal voltage, V2:
Power supply voltage for the light receiving element side circuit of the photo coupler, v1: voltage applied to the light emitting element, v2: input voltage to the inverter.

Claims (1)

[Scope of utility model registration request] 1. A series resistor and a parallel resistor for a light emitting element are provided in a light emitting element side circuit of a photocoupler, and a discharge resistor and a noise removing capacitor are connected in series in the light receiving element side circuit of a photocapra. In the photocoupler circuit provided with, a capacitor is connected in parallel to the parallel resistor for the light emitting element of the light emitting element side circuit, and the product of the voltage in the noise and the time width that can enter from the outside to the light emitting element side of the photocoupler circuit. The photocoupler circuit is characterized in that the time constant is selected so that the maximum value of the voltage noise on the parallel resistance within the time width is less than 1.5 times the light emission threshold of the light emitting element with respect to the maximum .