JPH05291876A - Signal isolation device - Google Patents

Abstract

PURPOSE:To attain stable signal isolation without effect of external noise with simple configuration with low power consumption. CONSTITUTION:The device is made up of a differentiation pulse output means receiving a pulse width signal and outputting a differentiation pulse at its leading edge and its trailing edge respectively, a 1st photocoupler 2 driven by the differentiation pulse outputted at the leading edge, a 2nd photocoupler 3 driven by the differentiation pulse outputted at the trailing edge, a flip-flop circuit 4 comprising 1st and 2nd switches SW1, SW2 set/reset by each pulse signal outputted from the 1st and 2nd photocouplers 2,3, and a pulse width/voltage signal conversion means provided with a 3rd switch SW3 turned on/off in response to the pulse width signal outputted from the flip-flop circuit 4, and the 1st, 2nd, 3rd switches SW1-SW3 are formed by using one IC including at least three sets of switch circuits or over.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal isolator applied to a signal converter for converting signals from various sensors such as temperature sensors installed in a process into standardized signals. Relates to a signal isolator in which the signal form is a pulse width signal, the pulse width signal is subjected to signal insulation via a photocoupler, and is converted back into a voltage signal for transmission.

[0002]

2. Description of the Related Art As a signal converter for converting signals from various sensors into standardized signals, for example, Yokogawa Technical Report Vol.32 No.4 (1988), pp. 53-58. Is disclosed in. The signal converter shown here amplifies the signal from the input sensor, performs linearization calculation processing, and then converts it into a pulse width signal proportional to the input signal using a voltage / pulse width conversion circuit, The signal is isolated by a photo coupler. And
The pulse width / voltage signal conversion circuit outputs the pulse width signal, which is signal-insulated by the photocoupler, and is returned to the voltage signal again.

[0003]

In the signal converter having such a structure, when the signal from the voltage / pulse width conversion circuit is at a high level (or low level), the light emitting element (LED) of the photocoupler is constantly operated. Since a current of about 10 mA flows, at the maximum pulse width (maximum duty ratio), the consumed current of about 10 mA continues to flow.

Therefore, the signal converter using the signal isolation circuit as shown in the prior art has a large power consumption in the entire device. This means that the power consumed in the signal converter is obtained from the signal sent via the two-wire transmission line, and the insulated signal is sent as a standardized signal via the two-wire transmission line. This is a problem when constructing a two-wire type signal converter.

The present invention has been made in view of the above problems, and has a small current consumption (a small current consumption that can be applied to a two-wire type signal converter) and the entire circuit. It is an object of the present invention to provide a signal isolator capable of having a simple structure.

[0006]

SUMMARY OF THE INVENTION The present invention which achieves such an object is a signal isolator in which a signal to be insulated is a pulse width signal and the signal is insulated by using a photo coupler. Differential pulse output means for receiving the pulse width signal and outputting differential pulses at the rising edge and the falling edge thereof, a first photocoupler driven by the differential pulse output at the rising edge, and output at the falling edge Flip-flop circuit composed of a second photocoupler driven by the differentiated pulse and first and second switches set / reset by respective pulse signals output from the first and second photocouplers And a pulse switch having a third switch that is turned on / off according to the pulse width signal output from this flip-flop circuit. And a width / voltage signal conversion means, said first, second, a signal isolation apparatus characterized by being configured using a single IC that includes at least three or more sets of switch circuit of the third switch.

[0007]

The differential pulse output means outputs differential pulses at the rising and falling timings of the pulse width signal. The first and second photocouplers are driven by these differential pulses, and the consumption current flows only for a short time during which the differential pulses are applied.

The pulse signals output from the first and second photocouplers at different timings are respectively applied to the set terminal / reset terminal of the flip-flop circuit and converted into pulse width signals here. The pulse width signal converting means converts the pulse width signal from the flip-flop circuit back into a voltage signal and outputs it.

[0009]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a configuration block diagram showing an embodiment of the present invention. In the figure, IN is an input terminal to which a signal to be insulated is applied as a pulse width signal, 1 is a pulse width signal, and differential pulse output means 2 outputs differential pulses at a rising edge and a falling edge thereof, and 2 is a rising edge. The first photocoupler (PC1) driven by the differential pulse output at the edge, 3 is the second photocoupler (PC2) driven by the differential pulse output at the falling edge, and 4 is the first and first A flip-flop circuit that receives each pulse signal output from the two photocouplers 2 and 3 as a set / reset signal and outputs a pulse width signal. In the present invention, this flip-flop circuit is the first and second It is composed of switches SW1 and SW2.

Reference numeral 5 has a third switch SW3 driven by the pulse width signal from the flip-flop circuit 4,
It is a PWM / voltage conversion means for converting the pulse width signal into a voltage signal. Reference numeral 6 is an analog switch IC in which at least three switch circuits are incorporated, for example, C ² M
The TC4053BP / BF of the OS digital integrated circuit is used, and the above-mentioned first to third switches SW1 to SW3 are used.
Is configured by using a switch circuit incorporated in this IC.

The differential pulse output means 1 is composed of a CMOS inverter IC10 and a differential capacitor C10, and a negative pulse direction / a positive pulse direction differential pulse is generated at the rising and falling edges of the pulse width signal applied to the terminal IN, respectively. Output a signal. The first photocoupler 2 allows the differential pulse generated at the rising edge of the light emitting element (LED) to flow in the forward direction, and the second photocoupler 3 causes the light emitting element (LED) at the falling edge. One end of the differentiating capacitor C10 is connected so that the differentiating pulse to flow in the forward direction.

That is, LE of the first photocoupler 2
The anode of D is connected to a voltage source V1 via a resistor R10 so that a differential pulse is applied to the cathode, and
The cathode of the LED of the second photocoupler 3 is a resistor R1.
It is connected to the voltage source V1 via 0 and is connected so that the differential pulse is applied to the anode. And the first,
Each phototransistor in the second photocoupler has an emitter connected in common and a collector connected to load resistors R1 and R2, respectively. The other ends of the load resistors R1 and R2 are connected to the voltage source V2. The voltage source V1
The voltage source V2 and the voltage source V2 are electrically insulated by, for example, a transformer.

The flip-flop circuit (F / F) 4 is composed of first and second switches SW1 and SW2,
They are driven by the signals output from the switches of the other party. The PWM / voltage converting means 5 is composed of a switch SW3 for turning on / off a constant voltage generated in the constant voltage diode D1, a resistor R4 for smoothing the turned on / off voltage signal, a capacitor C1 and an amplifier AMP1, and an output terminal. A voltage signal corresponding to the pulse width signal is output from OUT.

FIG. 2 is a diagram showing an equivalent circuit of a circuit formed between the photocoupler (PC) and the switch SW, and the relationship between the input signals A and B and the output signal X. The switch SW is equivalent to a gate circuit, and these circuits can be represented as a combination circuit of an inverter and a gate. Therefore, the flip-flop circuit can be configured by connecting the two sets of gate circuits with the output signals thereof as the input signals of the other gates and making a cross connection.

The operation of the thus constructed apparatus will be described below. FIG. 3 is a time chart showing an example of signal waveforms at respective portions in the device of FIG. Here, the resistance R
The voltage V1 of the voltage source to which one end of 10 is connected is set to 5
The voltage V2 of the voltage source connected to V and one ends of the resistors R1 and R2 is set to 10V.

Now, assuming that a pulse width signal as shown in (a) is applied to the input terminal IN, a CMOS
This pulse width signal is output by the inverter IC 10 from (b).
The pulse width signal is inverted as shown in FIG. 2, and this is the differential capacitor C10 that constitutes the differential pulse output means 1.
Pass through. As a result, as shown in (c), a negative differential pulse is output at the falling timing of the pulse width signal, and a positive differential pulse is output at the rising timing of the pulse width signal.

The negative differential pulse supplies a drive current as shown by the solid line to turn on the first photocoupler 2. Similarly, the positive differential pulse causes a drive current to flow as shown by a broken line to turn on the second photocoupler 3. As a result, the current flowing in the LED of the first photocoupler 2 has a differential waveform as shown in (d), and the current flowing in the LED of the second photocoupler 3 is also:
As shown in (e), the waveform becomes a differential waveform, and the current consumption is reduced in both cases.

Pulse-shaped signals are output from the first and second photocouplers 2 and 3 as shown in (f) and (g), and the flip-flop circuit 4 receives these pulse signals and sets them. / Reset. As a result, the flip-flop circuit 4 can obtain the pulse width signals as shown in (h) and (i) from its output end. PWM
In the voltage conversion means 5, the third switch SW3 is
The reference voltage and 0 V are alternately switched by the pulse width signal output from the flip-flop circuit 4 and extracted.
An analog output E0 proportional to the duty ratio of the pulse width signal can be obtained from the output terminal OUT by passing it through a smoothing circuit (low-pass filter) including a resistor R4, a capacitor C1 and an amplifier AMP1.

FIG. 4 shows first and second photocouplers,
6 is a time chart showing further details of the operation of the flip-flop circuit 4 composed of first and second switches.
In this embodiment, the first and second photocouplers PC1,
It is assumed that the load resistors R1 and R2 of PC2 are both connected to the emitter side. It is assumed that the pulse width signal as shown in (a) is applied to the input terminal IN. When the level of the pulse width signal is 0V, current does not flow through the LEDs of the first and second photocouplers and is applied to the terminals 1Y and 1Z of the first and second switches SW1 and SW2. All the voltages are 0V. If the connection state of each switch is as shown in the figure,
The Y terminal of the switch SW1 is 0V, and the 0V voltage is applied to the C terminal of the second switch SW2.

For this reason, since the Z terminal of the second switch SW2 is connected to the 0Z terminal shown in the figure,
A voltage signal of 10V is output. This voltage signal is
Is applied to the B terminal of the switch SW2. Therefore, the first
As for the Y terminal output of the switch SW1, the 1Y terminal is selected and the 0V voltage signal is output. Therefore, in the state of the illustrated circuit, one output terminal OUT of the flip-flop circuit is
A state in which a 0V level signal (L level) is output as shown in (h) and a 10V level signal (H level) as shown in (i) is output to the other output terminal bar OUT. Is stable at.

In such a state, when the waveform of the pulse width signal changes from low level to high level, the first
The photocoupler PC1 is turned on, and a 10V pulse is generated at the 1Y terminal of the first switch SW1. By the edge (1) of this pulse signal, the first switch SW1
10V to the 1Y terminal → 10V to the Y terminal → 10V to the C terminal of the second switch SW2 → 0Z for the second switch SW2
Selected from terminal side to 1Z side → second switch SW2
0V voltage is output to the Z terminal of the → first switch SW
0V to the B terminal of 1 → the first switch SW1 is selected from the 1Y side to the 0Y side → 10V is output to the Y terminal of the first switch SW1.

In this way, at one end of the load resistor R1,
When a 10 V pulse is generated, one output terminal OUT of the flip-flop circuit changes from 0 V to 10 V as shown in (h), and a high level signal (H level).
However, the state changes and becomes stable so that the 0V level signal (L level) is output to the other output terminal bar OUT, as shown in (i).

Similarly, when the waveform of the pulse width signal transits from the high level to the low level, each waveform changes as shown in edge (2), and one output terminal OUT of the flip-flop circuit has As shown in (h), a low level signal (L level) is output to the other output terminal bar OUT.
As shown in (i), the state changes and stabilizes so that a 10 V level signal (H level) is output. By such operation, the flip-flop circuit that receives the pulse signal output from each photocoupler and outputs the pulse width signal corresponding to the pulse width signal applied to the input terminal IN is
It is realized by two switches SW1 and SW2.

FIG. 5 is a configuration block diagram showing another embodiment of the present invention. In this embodiment, the pulse signals output from the first and second photocouplers 2 and 3 are commonly received between the first and second photocouplers 2 and 3 and the flip-flop circuit 4. Has a receiving resistor R10,
A pulse receiving circuit 7 for outputting a set / reset pulse to the flip-flop circuit 4 in accordance with the signal generated in the receiving resistance is provided.

With such a configuration, the first and second
Noises mixed in at the same timing via the second photocouplers 2 and 3 flow in opposite directions in the reception resistance and are canceled here. Therefore, there is an effect that is not affected by noise.

[0026]

As described in detail above, the present invention is
Two photocouplers are used, which are driven by differential pulses and are configured to take out only the differential pulse signal components transmitted at different timings, which can reduce the power consumption and allow the external It is possible to realize a signal insulation device that operates stably without being affected by noise. Further, the two switches forming the flip-flop circuit and the switch used for the PWM / voltage converting means are made to use the switch elements incorporated in one IC, so that the entire structure is simple. You can

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an embodiment of the present invention.

[FIG. 2] First and second photocouplers (PC1, PC
It is a figure which shows the equivalent circuit of the circuit comprised between 2) and the 1st, 2nd switch, and the relationship between the input signals A and B and the output signal X.

FIG. 3 is a time chart showing an example of signal waveforms at respective portions in the device of FIG.

FIG. 4 is a time chart showing details of operations of a flip-flop circuit including first and second photocouplers and first and second switches.

FIG. 5 is a configuration block diagram showing another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Differential pulse output means 2 1st photocoupler (PC1) 3 2nd photocoupler (PC2) 4 Flip-flop circuit 5 PWM / voltage conversion means 6 Analog switch IC 7 Pulse receiving circuit

Claims (2)

[Claims] 1. A signal isolator in which a signal to be insulated is a pulse width signal, and the signal is insulated by using a photocoupler, and the pulse width signal is received at a rising edge and a falling edge thereof, respectively. Differential pulse output means for outputting a differential pulse, a first photocoupler driven by a differential pulse output at a rising edge, and a second photocoupler driven by a differential pulse output at a falling edge, A flip-flop circuit including first and second switches set / reset by each pulse signal output from the first and second photocouplers, and a pulse width signal output from the flip-flop circuit. And a pulse width / voltage signal conversion means having a third switch for turning on / off the switch. , Signal isolation apparatus characterized by being configured using a single IC that includes at least three or more sets of switch circuit of the third switch. 2. A flip-flop circuit is provided with a set / reset pulse in accordance with a signal generated in the receiving resistor, which has a receiving resistor commonly receiving each pulse signal output from the first and second photocouplers. The signal isolator according to claim 1, further comprising a pulse receiving circuit for outputting.