JPH0458256B2 - - Google Patents

Description

[Detailed description of the invention] [Summary] A transistor circuit and a resistor are connected in series, a voltage regulator diode and a photocoupler are connected in parallel to the transistor circuit, and the potential difference between both ends of the power supply circuit is monitored, and the A line of the power supply line is connected. When the potential difference between both ends exceeds the breakdown voltage of the constant voltage diode due to an overcurrent caused by a ground fault or the like, the power supply circuit is protected by cutting off the transistor.

[Industrial application field]

The present invention relates to improvements in power supply circuits widely used in the trunks of electronic exchanges.

In general, the above-mentioned power supply circuit is capable of supplying a stable line current, and also prevents abnormalities on the line side, especially A.
There is a strong need for measures to protect power supply circuits from overcurrents caused by line-to-ground faults, etc.

[Conventional technology]

FIG. 3 is a circuit diagram of a conventional power supply circuit.

In the figure, 1 and 2 are transistors, 3 to 7 are resistors,
Reference numerals 8 and 9 indicate Chiyoke coils, and 10 indicates line resistance. Note that the figure shows only the power supply circuit connected to the A line side of the line, and the power supply circuit connected to the B line side is omitted.

In FIG. 3, transistor 1 is normally in a conductive state because an operating voltage is applied to it, but
Since the voltage of the transistor 2 is lower than the operating voltage, the line current I is supplied to the transistor 2 in a cut-off state. In this case, the track A
If a ground fault occurs on the line side, the current I increases, so first the potential difference across the resistor 3 increases, and the potential difference across the resistor 4 also increases, causing the transistor 2 to change from a cut-off state to a conductive state. Therefore, the potential difference across the resistor 5 applied to the transistor 1 is reduced to less than the operating voltage of the transistor 1, and the transistor 1 is cut off.As a result, the current I flows to the resistor 7 side, damaging the transistor 1. can be protected from.

[Problem that the invention seeks to solve]

However, as long as the line current is small, the resistance 7
However, as the line current increases, the power consumption increases, and in that case, the resistor 7 also becomes large, and therefore the power supply circuit also becomes large.

[Means for Solving the Problems]] FIG. 1 shows a diagram of the principle of the present invention. In the figure, a first series circuit includes a transistor and a resistor connected in series between a DC power source and a load, and a second series circuit includes a light emitting element, a constant voltage diode, and a resistor that constitute a photocoupler, and a second series circuit that includes a photocoupler. A third series circuit consisting of a light receiving element and a resistor constituting the transistor is connected in parallel, and the third series circuit is formed by connecting a connection point between the light receiving element and the resistor to the base of the transistor. , when the voltage difference between the transistor and the resistor of the first series circuit becomes equal to or higher than the breakdown voltage of the constant voltage diode of the second series circuit, the second series circuit and the third series circuit
By turning off the transistor by a photocoupler configured with a light emitting element and a light receiving element in a series circuit, and supplying current limited by the second series circuit and the third series circuit to the load, Conventional problems are solved.

[Effect]

According to the present invention, the transistors of the transistor circuit are normally used in a saturated state to minimize the power consumption there, and the A line of the line is connected in series with the A line of the line in case of an overcurrent due to a ground fault or the like. When the potential difference between the transistor circuit and the resistor exceeds the breakdown voltage of the constant voltage diode, the power supply system is activated by the operation of the constant voltage diode.
By switching from transistors to photocouplers, it is possible to protect the power supply circuit without increasing its size.

〔Example〕

FIG. 2 is a circuit diagram of a power supply circuit according to an embodiment of the present invention.

In the figure, 11 and 12 are resistors, 13 and 14 are transistors, 15 is a constant voltage diode, and 16 is a photocoupler. Note that the same reference numerals indicate the same objects throughout the figures.

In FIG. 2, normal transistors 13 and 14
is reliably brought into conduction by applying a small operating voltage, and the line current I of line A flows. Most of the current flows as the collector current I _C of the transistors 13 and 14 .

If line A of the line has a ground fault and the current I increases, the potential difference across the resistor 3 due to the current I will also increase,
When the potential difference between - becomes equal to or higher than the breakdown voltage of the constant voltage diode 15, the constant voltage diode 15 becomes conductive, and at the same time, the forward current I _F flows through the photocoupler 16, so the photocoupler 16 also becomes conductive.

When the photocoupler 16 becomes conductive, the potential difference between the emitters and bases of the transistors 13 and 14 decreases, so that the transistors 13 and 14
Since the transistors 13 and 14 are in a cut-off state, overcurrent is prevented from flowing through the transistors 13 and 14.

〔Effect of the invention〕

As explained in detail above, according to the present invention, the power supply circuit can be protected by preventing overcurrent from flowing into the power supply circuit by using the constant voltage diode and the photocoupler, which are smaller than the resistor.

[Brief explanation of the drawing]

FIG. 1 is a principle diagram of the present invention, FIG. 2 is a circuit diagram of a power supply circuit of the present invention, and FIG. 3 is a circuit diagram of a conventional power supply circuit. In the figure, 1, 2, 13, and 14 are transistors, 3 to 7, 11, and 12 are resistors, 8 and 9 are chain coils, 10 is a line resistance, 15 is a constant voltage diode, 16 is a photocoupler, and 100 is a A transistor circuit is shown.

Claims (1)

[Claims] 1 Transistor 1 between the DC power supply and the load 10
00 and a resistor 3 connected in series, a second series circuit consisting of a light emitting element, a constant voltage diode 15, and a resistor 11 constituting a photocoupler 16, and a light receiving element constituting the photocoupler 16. and a third series circuit consisting of a resistor 12 are connected in parallel, and the third series circuit is formed by connecting a connection point between the light receiving element and the resistor 12 to the base of the transistor 100, and When the voltage difference between the transistor 100 and the resistor 3 in the first series circuit becomes equal to or higher than the breakdown voltage of the constant voltage diode 15 in the second series circuit,
a photocoupler 16 composed of a light emitting element and a light receiving element of the second series circuit and the third series circuit;
A power feeding circuit characterized in that the transistor 100 is cut off by the above-described operation, and the current limited by the second series circuit and the third series circuit is fed to the load 10.