JPS62233968A - Current supply circuit - Google Patents

Abstract

PURPOSE:To reduce circuit scale and to attain low cost by supervising only one end of a telephone connection so as to detect grounding in a power supply circuit supplying a talking current to a telephone set. CONSTITUTION:When the supply voltage is V0=-48V and the system is in normal operation, since the resistance is selected as r1=r2, a point C shows a voltage below -24V and the potential of a point D is equal to that of the point C. If a point B is grounded and a telephone set 8 is hooked off, an overcurrent flows and a potential at a point A shows nearly zero V. If the point A is grounded, a comaprator circuit 11 comparing the potential at the point D with a reference potential V2 outputs zero V, a transistor (TR) Q3 is turned off to disconnect the route of point A-resistor r2-TR Q2 thereby stopping the power supply. The point C shows the potential of -24V X R3/(R4+R3), which is larger than -24V and equal to the potential at grounding before power supply stop. At the time of releasing the grounding, the potential at the point C reaches -24V or below and the comparator circuit 11 obtains the information of grounding release.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a current supply circuit, and more specifically, to an electronic SLIC (Subscriber).
This invention relates to a current supply circuit that has been improved in terms of protection against ground faults and cross-contact, which are the biggest weaknesses of LineInterface C1rcuit.

[Conventional technology]

In recent years, subscriber interface circuits have been computerized, and 5
The name LIC is commonly used. Electronic interface circuits can be constructed without using the windings of conventional circuits, making it possible to reduce the size of the circuits and are highly effective in increasing packaging density.

On the other hand, handling large amounts of electricity may cause heat generation and overvoltage.

It requires a circuit to prevent destruction due to overcurrent, so it is not necessarily an advantage.

FIG. 2 is a diagram showing an example of a conventional current supply circuit, in which 1 is a first current detection circuit, 2 is a second current detection circuit, 3 is a current comparison circuit, 4 and 5 are amplifiers, and 6 is a differential amplifier, 7 is a transfer function (H) giving circuit, 8 is a telephone, 9 is a transfer function control circuit, 10 is a pie-sumi source, R+, R2, R3, R4
, rl, r2 are resistors, R5, R6 are line resistances, Q
1 and Q2 are transistors. Further, VO is a power supply circuit, which is composed of, for example, earth GND (OV) and -48V.

Next, the operation of the conventional circuit will be explained.

First, the basic operation will be explained. Amplifiers 4, 5. Adder 12 .
A feedback circuit is formed through each of the adders 12 and 13, and a DC voltage (bias voltage) V+ is applied to the adders 12 and 13 by an external bias power supply 10. By applying the DC voltage v1, a voltage of ■ is generated between the terminals of the telephone 8, that is, between points A and B via a feedback circuit. In other words, earth ground
→Transistor Q+ →Resistor rl →Line resistance R5 →Electrifier 8 →Line resistance R6 →Resistor r2 →Transistor Q2
→Supplies communication current in the direction of power supply circuit vO. The differential amplifier 6 operates with the voltage (2) generated across the telephone 8 and the line resistances R5, R6 as input.

In the differential amplifier 6, when the resistance values of the line resistances R5 and R6 are small, the voltage V is made small, and the transfer function H of the system is set by the Goo circuit 7 with a transfer function (H) so that the communication current is about 40 mA at the maximum. Then, feedback is applied to each amplifier 4.5. Further, when the line resistance value is large, the voltage (2) is made large and feedback is applied to the amplifier 4.5 via the transfer function (H) imparting circuit 7 so as to secure a communication current of about 20 mA at the minimum. In this way, the communication current is controlled to be within a certain range.

Next, in the case of a ground fault or cross-contact, since the SLIC is an electronic circuit, it will be destroyed if an overcurrent flows, so protection in the event of a ground fault or cross-contact is required.

Next, the operation during a ground fault will be explained.

When a ground fault occurs, the potential at point A becomes GND (0■). Then, an excessive current flows through the resistor r2. This current value is detected by the second current detection circuit 2. On the other hand, the first current detection circuit 1 detects the current flowing through the resistor rl. The currents flowing through each of the resistors rl and r2 are normally equal, but a difference occurs in the event of a ground fault. This is monitored by the current comparison circuit 3.

Even in the event of a ground fault, transistor Q1 → resistor rl, although it is small,
→ Line resistance R5 → Telephone 8 → Line resistance R6 → Resistor r2
→ Current must be able to flow through transistor Q2. The reason is that when the transfer function control circuit 9 stops energizing, each resistor r
This is because the currents flowing through l+r2 both become O, ground fault information is lost, and energization starts again, causing so-called racing. Upon obtaining the ground fault information, the transfer function control circuit 9 changes the value of the transfer function (H) providing circuit 7;
Alternatively, the voltage v of the bias power supply 10 supplied from the outside
1 to suppress overcurrent.

Furthermore, even if there is common-mode noise induced in the line of the telephone 8, no difference in current flowing through each resistor rl+r2 will appear, so this differential detection method prevents erroneous detection of hook information.

However, for individual telephones such as PBXs and key telephones, the transmission distance is short and most of the transmission is done through indoor wiring, so there is no need to assume the above-mentioned excessive common mode noise. Therefore, PBX,
For single telephones such as key telephones, it is possible to create a circuit that is simpler and has more practical performance.

[Problem that the invention seeks to solve]

In this manner, in the event of a ground fault, in order for the transfer function control circuit 9 to maintain its operation during the ground fault, it was necessary to supply a current to the telephone set to an extent that would not damage other electronic circuits.

Therefore, there were problems with the cap having a large circuit scale and a complicated configuration.

This invention was made to solve the above problems, and aims to reduce the scale and cost of the conventional earth fault protection circuit.

[Means for Solving the Problems] A current supply circuit according to the present invention connects a high-potential side telephone connection terminal and a negative input terminal of a differential amplifier via a resistor, and also connects a low-potential side telephone connection terminal to a negative input terminal of a differential amplifier. Connect the connection end and the positive input end of the differential amplifier through a resistor, and further connect the positive input end to the midpoint potential point of the power supply circuit through the resistor, and connect the output point of the differential amplifier and the negative input end. A resistor is connected between the two terminals, one of the negative input terminal and the positive input terminal is connected to one input terminal of a comparator circuit, and a reference voltage is applied to the other input terminal of the comparator circuit.

[Effect]

In this invention, when a ground fault occurs at the connection end of the telephone, the potential at the connection end of the telephone fluctuates relative to the reference potential, and this is detected by the comparison circuit.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of the present invention. In this figure, the same reference numerals as in Fig. 2 indicate the same parts, and 1
1 is a comparison circuit that compares the potential of the dot and the reference potential v2;
R, , R8 are resistors, and Q3 is a transistor as a switching element.

Next, this operation will be explained using the case where the power supply voltage VO=-48V as an example.

During normal operation, the current 11 flowing through the resistor rl and the current 12 flowing through the resistor r2 are equal, and rl = r2, so point A is always at a potential of -24V to -48V. Therefore, point C indicates a voltage of -24V or less. Further, the point is at the same potential as point C.

If point A has a ground fault, point C will be -24VXR3/ (R4+R
1) shows the potential. This value is greater than -24V. When there is a ground fault at point B, there is no problem because no overcurrent will flow if the telephone 8 is on-hook, but an overcurrent will flow if it is off-hook. Even in this case, the potential at point A is approximately Ov
shows.

As is clear from section L, the potential at point C is lower than -24V in normal conditions and in the case of a ground fault, and becomes hotter than -24V, respectively. Furthermore, since the point C and the point are at the same potential, the point is monitored by a comparison circuit 11 with a high input resistance and outputs ground fault information. During normal operation, the comparator circuit 11 outputs -48V and turns on the transistor Q3, so that the transistor Q becomes active. That is, current is supplied in the order of transistor Q+→resistor rl→line resistance R5→telephone 8→line resistance R6→resistor r2→transistor Q2. When point A is grounded, overcurrent will flow from point A to resistor r2 to transistor Q2. On the other hand, the comparator circuit 11 which has received the ground fault information outputs Ov and turns off the transistor Q3, so that the transistor Q2 is turned off. As a result, the above point A→resistor r2→transistor Q
Route 2 will be cut off and power supply will be stopped.

Even if the power supply is stopped, if point A has a ground fault, point C will be -24.
Indicates the potential of VXR3/(Ra +R3). That is, it is greater than -24■. This is the same potential as at the time of a ground fault before the power supply was stopped. After the power supply is stopped and the ground fault is removed, point C
The potential of is less than -24V. The threshold value (reference current V7) of the comparator circuit 11 is set to -24V to -24VXR3/
Since it is set between (R4+R3), the comparison circuit 11
can obtain information on ground fault release. When the information that the ground fault has been removed is obtained and the output of the comparator circuit 11 becomes 148V, the transistor Q3 is turned on again and power supply starts.

As described above, power supply → ground fault → power supply stop → ground fault release power supply is automatically performed. The same applies when there is contact.

Note that the input terminal of the comparison circuit 11 is connected to the differential amplifier 6 in the embodiment.
Although it is connected to the (-) input terminal (D) of , the same effect can be achieved by configuring it to be taken out from the (+) input terminal "(C)."

〔Effect of the invention〕

As explained above, this invention connects the high potential side telephone connection terminal and the negative input terminal of the differential amplifier via a resistor,
In addition, connect the telephone connection end on the low potential side and the positive input end of the differential amplifier via a resistor, and further connect the positive input end to the midpoint potential point of the power supply circuit via a resistor. Connect a resistor between the output point and the negative input terminal, connect either the negative input terminal or the positive input terminal to the - input terminal of the comparison circuit, and connect the reference to the other input terminal of this comparison circuit. Since voltage is applied, ground faults can be detected by simply monitoring one end of the phone connection, which has the advantage of reducing circuit scale and lowering costs, making it ideal for PBXs and keychains. Suitable for use in telephones.

[Brief explanation of drawings]

Figure 1 shows #! of the current supply circuit of this invention. FIG. 2 is a circuit diagram showing an example of a ground fault detection circuit of a conventional current supply circuit. In the figure, 4.5 is an amplifier, 6 is a differential amplifier, 7 is a transfer function (H) giving circuit, 8 is a telephone, 11 is a comparison circuit, r+
, r2, R+ ~R4, R7, R8 are resistors, R5
, R6 are line resistances, Ql, Q2. Q3 is a transistor. Figure 1 Ql-Ql transistor

Claims (1)

[Claims] a power supply circuit that supplies a talking current to the telephone; a differential amplifier that amplifies the voltage difference between terminals connected to the telephone; In a current supply circuit comprising a feedback circuit, the telephone terminal on the high potential side and the negative input terminal of the differential amplifier are connected via a resistor, and the telephone terminal on the low potential side and the differential amplifier are connected via a resistor. The positive input terminal of the differential amplifier is connected via a resistor, and the positive input terminal is further connected to the midpoint potential point of the power supply circuit via a resistor, and the output point of the differential amplifier and the negative input terminal are connected to each other via a resistor. A resistor is connected between the two, one of the negative input terminal or the positive input terminal is connected to one input terminal of a comparator circuit, and a reference voltage is applied to the other input terminal of the comparator circuit. current supply circuit.