JPH0229784Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a protection circuit for a facsimile device that prevents circuit elements from being damaged by high voltage caused by lightning induced in a telephone line.

Generally, a facsimile device is connected to a telephone line L via a line network control circuit 3 that switches between a telephone 1 and a facsimile device 2, as shown in FIG. 1, and the line network control circuit 3 is composed of relays, transformers, etc. As a result, the telephone line L and the facsimile device 2 are insulated.

However, when lightning occurs and a high voltage of several kilovolts is induced in the telephone line L, the high voltage enters the facsimile device 2 via the DC power line 4 as a result of discharge inside the line network control circuit 3. , there is a problem that electronic components such as ICs and transistors of the facsimile device 2 are destroyed, and an improvement has been desired.

Therefore, the present invention was developed in view of this point.
A protection circuit for a facsimile device is provided which is configured to absorb induced high voltage and protect the facsimile device by preventing it from entering the facsimile device.

Embodiments of the present invention will be described below with reference to the drawings.

In addition, the same components as in Fig. 1 are indicated by the same figure numbers.
The points improved by the present invention will be explained.

5 is a surge absorber connected between the power lines of the line network control circuit 3 and having the characteristics shown in FIG. has been done.

A switching diode 6 is connected between the power terminal of the facsimile device 2 and the surge absorber 5, and its anode electrode is connected to the facsimile device 2, and its cathode electrode is connected to the line network control circuit 3, and is set to be non-conductive. This prevents intrusion into the high voltage facsimile device 2. Reference numeral 7 denotes a diode whose cathode electrode is connected to the cathode electrode of the switching diode 6 and connected in parallel to the surge absorber 5, and is configured to conduct to a high voltage of opposite polarity.

Next, the operation of the present invention having such a configuration will be explained.

First, when operating normally, the switching diode 6 is conductive and power is supplied to the facsimile device 2 and the line network control circuit 3. However, since this power supply voltage is lower than the operating voltage of the surge absorber 5, surge The absorber 5 is non-conducting, and the diode 7 is also non-conducting because it has a reverse voltage.

However, when a high voltage is induced in the telephone line L due to lightning, and a high voltage is induced in the power supply line 4 via the line network control circuit 3, the surge absorber 5 becomes conductive and clamps to the voltage of the surge absorber 5.
Since the clamped voltage is higher than the power supply voltage, the switching diode 6 becomes non-conductive and prevents the induced high voltage from entering the facsimile device 2.

Note that when a high voltage of opposite polarity is generated, the diode 7 becomes conductive to prevent the power supply voltage of the facsimile device 2 from swinging to a negative potential, thereby protecting the facsimile device 2.

Further, the parallel circuit of the surge absorber 5 and the diode 7 is equivalent to a Zener diode, and can be replaced with a Zener diode.

Furthermore, it can be applied not only to power lines but also to signal lines.

As mentioned above, the facsimile device protection circuit of the present invention uses a surge absorber whose operating voltage is higher than the power supply voltage and a switching diode to prevent high voltage from entering the facsimile device. This structure is designed to prevent intrusion into the facsimile device, and the facsimile device can be protected with a simple structure, which is extremely effective in practical use.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a conventional example of a facsimile machine;
FIG. 2 is a diagram showing a facsimile device embodying the present invention, and FIG. 3 is a diagram showing characteristics of a surge absorber. 1...telephone, 2...facsimile device, 3...
...Line network control circuit, 5...Surge absorber.

Claims (1)

[Scope of utility model registration request] In a facsimile device connected to a telephone line via a line network control circuit, a power line is directly connected to the facsimile machine, and a switching device whose anode electrode is connected to the power line of the facsimile machine is connected to the line network control circuit. A surge absorber whose operating voltage is slightly higher than the voltage of the power supply line is connected between the power supply of the line network control circuit and a diode whose cathode electrode is connected to the cathode electrode of the switching diode. A protection circuit for a facsimile device, characterized in that a parallel circuit is provided, and the switching diode is made non-conductive when the surge absorber is made conductive, thereby cutting off a power line between a line network control circuit and the facsimile device.