JPS5953012A - Overcurrent protecting circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] ta+ Technical Field of the Invention The present invention relates to an overcurrent protection circuit, in particular, a photocoupler is inserted into a current supply path, and the current supply +? Is there an overflow in the current monitoring circuit that monitors the DC current flowing through 3? l'l: Pertains to the %f protection circuit.

(b) Prior Art and Problems FIG. 1 is a diagram showing an example of an overcurrent protection circuit of this type, which is included in the 1/8th current monitoring circuit. FIG. 1 shows a current for monitoring direct current supplied from a power supply circuit 1, such as a trunk circuit, to a power receiving circuit 4, such as a telephone, via a current supply path consisting of an A line 2 and a B line 3. A supervisory circuit is indicated. In FIG. 1, when the contact 6 is closed in the power receiving circuit 4, the voltage ∆ in the power feeding circuit 1/8I;
(ε old V()) to ll'l current is Δ line 2 and B
It is supplied to the fl load circuit 5 via line 3. Photocouplers 8 and 9 are inserted into the lead wire 2 and I3 wire 3, respectively, and when the DC current flows, they are energized to drive the monitoring circuit 10 and indicate the supply of DC current. In the power receiving circuit 4, the load circuit 5 is closed by closing the contact 7.
may be short-circuited, and the direct current flowing through the A line 2 and B line 3 may increase. In such a case, photocouplers 8 and 9
In order to prevent damage caused by a DC current exceeding a specified value flowing through the photocouplers 8 and 9, and resistors 11 and 14 inserted in series with the photocouplers 8 and 9, constant voltage diodes I-13 and I-14 are installed, respectively. 14 are connected in parallel. As a result, even if the DC current flowing through the A line 2 and the B line 3 increases, the DC current applied to the ii'j column circuit 1/F of the 1-coupler 8 and the resistor 11 or the series circuit of the photocoupler 9 and the resistor 12 will increase. The voltage is determined by the constant voltage diode I3 or 1
By setting the resistance values of resistors 1 and 12 to appropriate values, the DC current flowing through photocouplers 8 and 9 is limited to within a specified value.

As is clear from the above description, in the conventional overcurrent protection circuit, the constant voltage diodes 13 and 14 and the resistors 11 and 12 limit the direct current flowing through the photocouplers 8 and 9 to within a specified value. However, the breakdown voltage of the constant voltage diodes 13 and 14 (e.g. 2
volt or more) is relatively higher than the voltage drop of the bottom couplers 8 and 9 (for example, 1.1 to 1.5 volts), so the DC current flowing through the bottom couplers 8 and 9 is set to the specified value (
For example, in order to limit the resistance to within 50 milliamps, it is necessary to make the resistors 11 and 12 considerably high resistance (for example, 9 to several hundred ohms). However, as the resistance JjC value of the resistors 11 and 12 increases, the power supply circuit 1 to the power receiving circuit 4
When transmitting a signal (for example, an audio signal) etc. via the A line 2 and B line 3, the direct current supplied to the A line 2 and B line 3 must be 3, the allowable resistance value iη decreases, and the power supply circuit 1
Another drawback is that the influence on the installation range of the power receiving circuit 4 increases.

(C1 Purpose of the Invention The purpose of the present invention is to eliminate the drawbacks of the conventional overcurrent protection circuit as described above, to reduce the resistance value inserted into the current supply path as much as possible, and to reduce the resistance value inserted into the current supply path to the extent that the installation range of the power supply circuit and power receiving circuit is The goal is to reduce the impact as much as possible.

The object of the present invention is to provide a current monitoring circuit that includes a photocoupler inserted in a current supply path and monitors a direct current flowing through the current supply path. This is achieved by connecting a plurality of diodes connected in series in the forward direction in parallel to a resistor and controlling the direct current flowing through the coupler.

te+ Example of invention An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram showing an overcurrent protection circuit according to an embodiment of the present invention. Note that the symbols between 2' and ζ indicate the same object throughout the figures. In FIG. 2, a current supply path for supplying direct current from the power supply circuit l to the power reception circuit 4 is configured,
Photocoupler 8 for DC current detection inserted into A line 2
Diodes 15 and 16 connected in series in the forward direction are connected in parallel to the current limiting resistor 11, and B
To the photocoupler 9 and resistor 12 inserted into the line 3,
Diodes 17 and 18 connected in series in the forward direction are connected in parallel. The diodes 15 to 18 are also connected to the incoming lines 2 and B by closing the contacts 7 in the power receiving circuit 4, for example.
When the DC current flowing through wire 3 increases, photocoupler 8
and the resistor 11, or the DC voltage applied to the series circuit consisting of the poto coupler 9 and the resistor 12.
By maintaining the resistance values of the resistors 11 and 12 at appropriate values, the direct current flowing through the photocouplers 8 and 9 is limited to within a specified value. Since the forward voltage of the diodes 15 to 18 is, for example, 0.6 to 0.8 volts, the DC voltage applied to the series circuit is maintained at a value sufficiently close to the voltage drop of the photocoupler 8 or 9. As a result, in order to limit the DC current flowing through the I-coupler 8 and 9 within a specified value, the resistance value that should be set for the resistors 11 and 12 may be, for example, ten to several tens of ohms. Therefore, the transmission tR loss is also reduced. According to actual measurements, for example, the resistance 11
and 12, respectively, from 40 ohms (FIG. 1) to 10 ohms (FIG. 2), the transmission loss is improved by 0.7 dB.

As is clear from the above description, according to this embodiment, the resistance values of the resistors 11 and 12 inserted into the A line 2 and the B line 3 are set to the tolerance 1↓(
Since the resistance value is maintained sufficiently low compared to the resistance value, the influence on the installation range of the power feeding circuit 1 and the power receiving circuit 4 is also small. By improving the resistors 11 and 12 from 40 ohms to 10 ohms as in the previous example, a short distance of about 340 meters is extended using a 0.5 mm φ cable.

Note that FIG. 2 is only one embodiment of the present invention; for example, the power feeding circuit 1 is not limited to a trunk, the power receiving circuit 1/fj 4 is not limited to a telephone, and many other modifications may be considered. However, the effects of the present invention do not change in either case.
The performance of the couplers 8 and 1) and DA-1. The fruit remains the same.

(fl) Effects of the Invention According to the present invention, in the current monitoring circuit, the resistance (r?f) inserted into the current supply path is sufficiently reduced, and the influence on the installation range of the power feeding circuit and the power receiving circuit is minimized. Is it possible to maintain it?

[Brief explanation of the drawing]

FIG. 1 does not show an example of a conventional overcurrent protection circuit, and FIG. 2 does not show an example of an overcurrent protection circuit according to an embodiment of the present invention.
It is So1. In the figure, ■ is the power supply circuit, 2 is the input line, 3 is the B line, A is the power receiving circuit, 5 is the load circuit, G and 7 are contacts, 8 and 9 are photocouplers, 1υ is the monitoring circuit 1, 11 and engineering 2. For example, resistors 13 and 14 are constant voltage diodes, and diodes 1-115 to 18 are not shown.

Claims (1)

[Claims] Insert a photocoupler into the current supply path, and connect the current supply 11+8
In the current monitoring circuit 1-δ flowing through i+'+ current total current f: An overcurrent protection circuit characterized in that a plurality of diodes 1' are connected in parallel to control the direct current flowing through the photocoupler.