JPS6022853B2 - Square wave signal isolated transmission circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for insulating and transmitting a rectangular wave signal that step-changes between two different levels in equal time widths.

Conventionally, as a circuit of this type, the electrical circuit shown in FIG. 1, which uses an optical coupling element (for example, a photocoupler) for isolated transmission, is generally known. In FIG. 1, 1 is an optical coupling element (
For example, an impedance element (resistance element) 2 is connected between one output terminal of the photocoupler and the positive potential +V.
The point A is connected to the input side of the inverting element 3. Further, the other output terminal of the optical coupling device 1 is connected to a reference potential 4. When a rectangular wave signal (at a low frequency) with a waveform as shown in Fig. 2a is input to this circuit input terminal, it is transmitted by the optical coupling element 1, and is transmitted to the output side connection point A as shown in Fig. 2b. A square wave like this is obtained. The waveform of this is inverted by the inverting element 3, and the output terminal of the inverting element 3 and the reference potential 4
A rectangular wave output as shown in FIG. 2c is obtained between . However, as the frequency of the input rectangular wave signal gradually increases (waveform shown in Figure 3a) and becomes high enough to affect the operating speed of the optocoupler, the width of the output signal becomes smaller and the waveform at connection point A. 3 becomes small as shown in FIG. 3b and does not intersect with the input detection level of the inverting element, so that the waveform at the output terminal of the inverting element 3 becomes as shown in FIG. 3c, and the rectangular wave signal is not transmitted accurately. Therefore, the frequency of the square wave signal is limited by the response speed of the optical coupling element, so if you want to transmit the square wave signal to the high frequency range, you must use an optical coupling element with a fast response speed.
At this time, there was a drawback that the cost was high. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide an inexpensive rectangular wave signal insulated transmission circuit that is capable of insulating transmission even at high frequencies. According to the present invention, the above object is achieved by connecting the input sides of two optical coupling elements to each other in an antiparallel relationship so that both optical coupling elements operate alternately in response to mutually different levels of the input signals. This is achieved by conducting the output signals of both coupling elements to a comparator element and obtaining an output signal isolated from the input signal from the comparator element. Embodiments of the present invention will be described below based on the drawings.

FIG. 4 is an electrical circuit diagram of a rectangular wave signal isolated transmission circuit according to an embodiment of the present invention, and FIGS. 5 and 6 are waveform diagrams.
The configuration of this circuit is such that an impedance element 2 is connected between one output terminal of the first optical coupling element 1 and 10 V at a point A, and the point A is connected to one input terminal of the signal comparison element 13. Connect to. Further, the other output state of the optical coupling element 1 is connected to the reference potential 4. The second optocoupler 11 has its input terminal connected to the input terminal of the first optocoupler 1 in parallel with each other in opposite directions, and has one output terminal connected to a positive potential of 1 V. Connect the impedance element 12 at point B,
The point is connected to the other input terminal of the signal comparison element 13. Further, the other terminal of the optical coupling element 11 is connected to the reference potential 4. In this circuit, a rectangular wave signal having a waveform as shown in FIG.
(low frequency), it is transmitted by the optical coupling element 1, and a rectangular wave shown by the solid line in FIG. At point B, a rectangular wave having the opposite polarity as shown by the broken line in FIG. 5B is obtained. The signal comparison element 13 compares and determines the level difference between the signals, and compares the output terminal with the reference potential 4.
A signal having a waveform shown in FIG. 5c is output between the two. Next, in the case of a high-frequency rectangular wave input, for example, when a rectangular wave signal as shown in FIG. 6a is input, a sawtooth signal with an operation delay ( Solid line is A
At the connection point, the broken line is at the connection point B), but the signal comparison element 13 determines the level difference of each signal, and generates a rectangular wave as shown in FIG. 6c between its output terminal and the reference potential 4. Output a signal. According to the circuit described above, the optical coupling element can be of a commonly used type with a response speed, is inexpensive, and
Moreover, it is possible to provide a stable rectangular wave isolated transmission circuit that can transmit isolated signals even at high frequencies.

[Brief explanation of the drawing]

Figure 1 is an electric circuit diagram of a conventional isolated rectangular wave signal transmission circuit, and Figure 2 a, b, and c are input terminals, A connection point, and output terminals when a low frequency rectangular wave signal is input to the same transmission circuit. Figures 3a, b, and c are waveform diagrams at the input terminal, connection point A, and output terminal when a high-frequency rectangular wave signal is input to the same transmission circuit, and Figure 4 is an embodiment of the present invention. Electrical circuit diagram of a certain rectangular wave signal isolated transmission circuit, Figure 5 a, b
, c are waveform diagrams at the input terminal, A connection point, B connection point, and output terminal when a low frequency rectangular wave signal is input to the same transmission circuit. Input terminal, A connection point, B connection point when inputting a signal,
FIG. 3 is a waveform diagram at the output terminal. 1...First optical coupling element, 11... Second optical coupling element, 2, 12... Impedance element, 1
3... Signal comparison element, 4... Reference potential. Outer 1, Figure 2, Figure 3, Figure 5, Figure 5, Figure 6

Claims (1)

[Claims] 1. In a circuit for insulating transmission of input signals that step change between two different levels in equal time widths using optical coupling elements, the input sides of the two optical coupling elements are connected in an antiparallel relationship with each other. the two optical coupling elements are configured to operate alternately in response to mutually different levels of the input signal, and the output signals of the two optical coupling elements are guided to a comparison element, and from the comparison element A rectangular wave signal isolated transmission circuit characterized in that an isolated output signal is obtained.