JPH0817636A - Modem with an isolation transformer inserted in the transmitter / receiver circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] It is to prevent the disturbance of the pattern and the damage of the element of the modem used for the data transmission circuit, which cannot be sufficiently removed by only the capacitor and the varistor. [Structure] In a modem in which an insulation transformer is inserted in a transmission / reception end circuit, the primary winding 2 of the insulation transformer 25 (26)
3 and the secondary winding 24 are provided at both ends of the iron core so as to be separated from each other, and the capacity between them is an insulating transformer which can be determined by the expected maximum value of electric induction noise received from the outside. If the floating capacitance is set to be less than a few PF, it is practically used in a wide range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modem, and more particularly to a modem in which an insulating transformer is inserted in a transmission / reception terminal circuit.

[0002]

2. Description of the Related Art FIG. 3 is a wiring diagram of a schematic transmitting / receiving end portion of a conventional modem. In the figure, 1 and 2 are conventionally used insulating transformers, 3 to 6 are capacitors for eliminating voltage noise, and 7 to 12 are varistors for eliminating surge voltage. In such a modem, various electrostatic induction noises easily enter from the line side and the device side through the insulating transformer, which disturbs the bit pattern in the modem and damages the elements in the modem.
The capacitor and varistor described above are used as a measure for eliminating the disturbance of the bit pattern in the modem and the damage of the element.

[0003]

However, the above-mentioned elimination measure, that is, immunity measure using the capacitor and varistor cannot sufficiently remove the disturbance of the bit pattern in the modem and the damage of the element. Further, since there are many capacitors and varistors used for immunity, it has been desired to reduce the number of these elements in terms of structure and cost.

The present invention is to prevent the disturbance of the bit pattern in the modem and the damage of elements which cannot be sufficiently removed by only the capacitor and the varistor, and to reduce the use of the capacitor and the varistor.

[0005]

According to the present invention, in a modem in which an insulation transformer is inserted in a transmission / reception terminal circuit, the insulation transformer is provided with a primary winding and a secondary winding separated from both ends of an iron core. A modem having an insulating transformer inserted in a transmission / reception end circuit is obtained, which is an insulating transformer in which a capacity generated therebetween is determined by an expected maximum value of electric induction noise received from the outside.

The above capacitance value cannot be said to be a matter of course because it varies depending on the shape of the insulating transformer and the allowable amount of disturbance of the pattern, but it is about 2 to 6 PF in the shape of a modem that is generally used at present. Is preferred.

[0007]

1 is a schematic diagram showing a partial connection diagram of a transmission / reception end of a modem according to an embodiment of the present invention. Isolation transformer 2
The stray capacitance between primary winding 23 and secondary winding 24 of 1 and 22 is set to about 3 PF. This value is determined by the expected maximum value of electrical induction noise received from the outside world. 25 and 26 are varistors, which suppress the surge generated in the normal mode on the line. If the iron core 27 of the insulating transformers 21 and 22 is grounded to the frame ground, the immunity is further improved.

FIG. 2 is a diagram showing an example of the structure of one of the transformers in FIG. The primary winding 23 and the secondary winding 24 are set separately on a common iron core 27. 28 is a bobbin, and 29 and 30 are lead wires. The space L between the primary winding 23 and the secondary winding 24 is about 2 mm apart when used normally.

The transformer shown in FIG. 2 is known as a leakage transformer for a charging power source, but it is completely different in the function to be used, and the size is literally out of order.

Next, the improvement of noise immunity in this embodiment will be described. The line between the modems performs data communication at a transmission speed of 9600 BPS,
Between any part of the track and the ground of the modem frame,
Peak voltage of commercial frequency rated 100V and 200V and switching power supply main oscillation voltage 1000V (frequency 1
00 KHz) and a sine wave oscillator output voltage of about 10 V or less (frequency 1 to 2 KHz) were individually applied for a long time, but no disturbance was observed in the bit pattern in the modem.
As an element for preventing common mode electrostatic induction noise, a varistor 23 is provided on both lead wires 29 and 30 shown in FIG.
Adding 24 and 24 is sufficient. That is, in the case of FIG. 3, it is not necessary to use four capacitors and four varistors.

In the above embodiment, the value of the floating capacitance of 3PF shown in FIG. 1 can be used in almost all cases in a normally used modem. Is obtained. In actual use, it is preferable that the primary winding and the secondary winding are separated as much as possible, the facing area is made as small as possible, and the drift capacitance is set as small as possible. In this way, it is possible to deal with unexpected noise. However, if it is used only in a place where the noise does not become particularly large, a larger capacity is acceptable. Generally, it is safe to set the capacity to 2 to 6 PF.

[0012]

As described above, the primary winding and the secondary winding of the insulating transformer to be used are provided separately on the iron core, and the stray capacitance or the interval between them is set to the magnitude of noise that is assumed. Therefore, by setting an appropriate value, it is possible to remarkably improve the immunity of the data transmission line using this modem in the data transmission line.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a partial connection diagram of a transmission / reception end of a modem according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a structure of one transformer in FIG.

FIG. 3 is a wiring diagram of a transmission / reception end portion of a conventional modem.

[Explanation of Codes] 1, 2 Insulation Transformer 3-6 Capacitor 7-12 Varistor 21, 22 Insulation Transformer 23 Primary Winding 24 Secondary Winding 25, 26 Varistor 27 Iron Core 28 Bobbin 29, 30 Lead Wire

Claims (2)

[Claims] 1. A modem in which an insulating transformer is inserted in a transmission / reception end circuit, wherein the insulating transformer has a primary winding and a secondary winding separated from both ends of an iron core, and receives a capacitance generated between them from the outside world. A modem in which an isolation transformer is inserted in the transmission / reception end circuit, which is an isolation transformer determined by the expected maximum value of noise. 2. The modem according to claim 1, wherein the floating capacitance is 2 to 6 PF or less.