JPS59186B2 - Ground fault detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a path detection circuit used in a subscriber circuit such as a telephone exchange, and particularly to a path detection circuit suitable for semiconductor integrated circuit implementation.

Telephone exchanges are being digitized to reduce costs, make them more compact, and increase reliability, but the computerization is mainly in the control section, which has a direct interface with subscriber terminals. Electronic subscriber circuits, especially semiconductor integrated circuits, are lagging behind. FIG. 1 shows a path detection circuit that is part of a conventional subscriber circuit. The path detection circuit detects the state in which the battery wire of the two power supply lines (battery line A and ground wire B) connecting the subscriber terminal and the exchange center is grounded to the ground due to a fault (hereinafter referred to as an oil path). In the detection circuit, to explain using Fig. 1, if the battery wire has an equal ground resistance and has an oil fault, the ground G → battery wire A →
Transformer T → Resistor R. An oil path current flows through the path of →resistance R3 →battery VBB. When oil path current flows, resistances R2 and R3
, R2', R3' between the input terminals of the operational amplifier OPAMP. The potential difference required to reverse the resultant output E. An oil leak detection signal is output. However, in the conventional example shown in FIG. 1, the battery VBB has a high voltage of 48V, so in order to suppress power consumption, resistors R2 and R are used. ,R. ′,
R. ' needs to have a high resistance (~100KQ), and in order to suppress variations in oil fault detection sensitivity, resistors R2 and R3 are required.
, R2', and R3' require high precision. Also, if a loop current is flowing, that is, if the ground wire A is connected to the telephone
Since a current is detected even when a communication current is flowing through the battery wire B, it is not possible to determine whether it is detected by the loop current or the oil path current, so when the loop current is formed, There were drawbacks such as the need to separate the path detection circuit shown in FIG. 1. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a ground fault detection circuit suitable for semiconductor integrated circuit implementation.

The present invention includes a current-voltage conversion means for generating a voltage proportional to the battery line current using a preset reference voltage source as a reference, a voltage generating means for generating a voltage proportional to the grounding line current, and a voltage proportional to the battery line current. A ground fault detection circuit is constituted by a two-manpower type voltage comparison means in which a voltage proportional to the ground wire current is applied to one input to the other human power, and when a terminal device ground fault occurs, the battery wire current is applied to the ground wire. When the current increases by a preset current value, the output of the voltage comparison means is inverted to detect a ground fault.

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

FIG. 2 shows a first embodiment of the ground fault detection circuit according to the present invention.

Under normal operating conditions, there is no ground fault resistance and the terminal telephone equipment is connected to the subscriber circuit of the exchange via battery line A and ground line B. In this circuit, when you pick up the receiver of the telephone set, the hook switch (not shown) inside the telephone set is turned on, and ground G' → resistor RlO' → transformer T → ground wire B → telephone set → battery wire A → Transformer T→
A loop current flows through diode D → resistor RlO → battery N. Now, due to the occurrence of a fault, battery line A has a ground fault resistance R. If a ground fault occurs while holding the loop current, in addition to the above loop current, a ground fault current of 1G flows through the ground G → battery wire A → transformer T → diode D → resistor RIO → battery BB, and the battery line current 1 flows through the ground wire. It becomes larger than the current (IA-1B). Therefore, when this current difference (IA-1B) becomes much larger than a preset current value, a ground fault is detected (9). Transistor Q. , resistor Rll, and resistor Rl2 are voltages proportional to the battery line current that are connected to the transistor Q using the reference power supply EFJ as a reference.
A current-voltage conversion circuit is constructed on the base of 1. On the other hand, a voltage proportional to the ground line current is generated at the base of transistor Q2 by resistor RlO'. Transistors Q1 and Q2 constitute a two-person voltage comparator circuit, and 4
When the base potential of transistor Q1 is lower than the base potential of transistor Q2, transistor Q1 is turned on to perform voltage comparison. That is, transistor Q1
The base current is a voltage proportional to the battery line current and the reference power supply V
Since the sum of REF becomes O voltage, the battery line current 1A becomes the reference power supply V from the ground line current 3. When the current value increases by the preset value by F, the transistor Q
Since the base potential of transistor Q1 is lower than the base potential of transistor Q2, a ground fault is detected by turning on transistor Q1 and inverting the output of the voltage comparison circuit. A trigram,
Transistors Ql and Q4 convert the on/off output of transistor Q1 into TTL (Tran-SistOr-Trans).
istOr-LOgic) is a circuit that converts to a logic level. Next, the operation of the circuit shown in FIG. 2 will be explained in detail. Now, there is a ground fault condition and transistor Q. Assume that the forward voltage drop between the base and emitter of the transistor Q is equal to the forward voltage drop of the diode DO. , Ql, Q2 current amplification factor (
HFE) is sufficiently large, the transistor Q.
The base potential VBl of the transistor Q1 and the base potential B2 of the transistor Q1 are respectively K! 0゜K12V B1+- 1A+VREF・・・・・・(1
)R. ．． VB2+- RlO'IB・・・・・・・・・
...(2) becomes.

Here, R, l = Rl2, RlO = RlO' and Solepa V3
l-1RlOlA+VREF・・・・・・・・・・・・
(3) VB2-RlOl3・・・・・・・・・・・・
(4), and for transistor Q1 to turn on, -VBl
〉-VB2, so the ground fault detection condition is -1BVREF
becomes.

i.e. battery line current 1A or ground RlO VREF From line current 1B? When it gets bigger, the land R10 A rainbow is detected when a connection is detected.

Here, the resistors Rll and Rl2 must be selected sufficiently large compared to the resistors RlO and RlO', but RlO - RlO
When '=200Ω, Rll=Rl2 is on the order of several Ω, which is a resistance value that is easy to integrate. In this case, the relative accuracy of the resistance accuracy, which was a problem in the conventional example, becomes a problem, but this can be easily obtained when integrated circuits are used. Furthermore, in the circuit shown in Figure 2, ground fault detection is performed using battery line current. Since it is detected by the difference current (IA-1B) between
It is not detected when normal loop current is applied (A:IB),
There are advantages such as the problem that a ground fault is not detected even when a loop current is flowing even during a non-ground fault as in the conventional example. FIG. 3 shows a second embodiment of the ground fault detection circuit according to the present invention applied to an electronic current supply circuit.

The part 1 surrounded by the dashed-dotted line in Fig. 3 is an electronic circuit that achieves the equivalent function of the transformer T in Figs. 1 and 2, and is called an electronic current supply circuit. This is explained in detail in the pending Japanese Patent Application No. 53-115766. To briefly explain the operation here, the transistor Q5,
Q6 constitutes a negative feedback circuit and is connected to the resistor R shown in Figure 1 from the telephone equipment. It has a DC internal resistance equal to , and operates so as to have an AC impedance equal to that of the transformer T. Transistors Q7 and Q8 also have the same circuit function as the transistors Q5 and Q6. In this electronic current supply circuit, a current approximately equal to the battery line current 1A flows through the resistor R2O, and a current approximately equal to the ground line current 13 flows through the resistor R2J.
Therefore, in the ground fault detection operation in FIG. 3, the resistor R2O' functions as the resistor RlO' in FIG. 2, and the resistor R2O functions as the resistor RlO in FIG. The explanation of the operation will be omitted in 2 because it is the same as . However, this third
In the circuit shown in the figure, the area between the base and emitter of transistor Q5 of current supply circuit 1 functions as diode D in FIG. It has the advantage of being omissible. Further, in Fig. 2, the reference power supply VRE
Since F is generated from the power supply VcO by the reference voltage generation circuit of transistor Q9, there is no need for a dedicated reference power supply.Furthermore, a 5V power supply is sufficient for VOO, so additional calculations as shown in Figure 1 are required. 'Power source V for width gauge. O-15V, VEE-1
5 is unnecessary. FIG. 4 shows a third embodiment of the ground fault detection circuit according to the present invention.

This embodiment is a simplified version of the embodiment shown in FIG. 2, and the operation of the circuit shown in FIG. The circuit is basically the same as the circuit shown in Figure 2, but the circuit configurations of the current-voltage converter circuit that generates a voltage proportional to the ground line voltage 13 and the voltage comparator circuit are different, especially the voltage comparator circuit. It is distinctive in that it is simplified. The voltage proportional to 1A of battery wire current is:
In the same manner as in Fig. 2, the resistor R3 is
This voltage is applied to the base of transistor Q1, which is a voltage comparator circuit. Further, a voltage proportional to the ground line current 3 is generated at the emitter of the transistor Q6 of the current/voltage generating circuit consisting of the transistor Q5 and the resistor R33, and this voltage is applied to the emitter of the transistor Q. Ditransistor Q with 1A>IB depending on the ground fault condition
When the base potential VBl of the transistor Q1 is lowered by the forward voltage drop V3El between the base and emitter of the transistor Q1 than the emitter potential 01 of the transistor Q1, the transistor Q1 is turned on and a ground fault is detected. Next, detection sensitivity will be explained in detail. Transistor Q. , QlQ6 as VBEO, V3ElVBE6, and the forward voltage drop of diode D as VFO, respectively. ,Ql,Q6
Assuming that the current amplification factor (HFO) is larger than the current amplification factor (HFO), the base potential Bl and emitter potential V of the transistor Q1. l
Is it 1?0. ．． B1+VREF-2(IAR3O+VFD-VBEO)
R3!・・・・・・(5) VE! +VBE6-1BR30' ゜゜゜゜゜゛(6).

When transistor Q1 turns on, that is, VEl-VB
Since ground fault is detected when l≧VBEl, SVBEO is now
OVBE! 0VRE6 ground VFDPR31R32,R30
'-R3O, the ground fault detection condition is VRICFIA-1
B≧? becomes.

Similarly to FIG. 2, a ground fault is detected when the battery line current 1A increases by a current value preset by the ground line current 13 and the reference power source ROF.

As described above, the circuit shown in FIG. 4 has the advantage that the circuit can be simplified. FIG. 5 shows a fourth embodiment of the ground fault detection circuit according to the present invention, which is characterized in that the reference power supply VROF is set with respect to the battery VBB.

That is, the circuit shown in FIG. 5 is the transistor QO of FIG.
, Q6, and Ql are replaced with transistors complementary to these, and the circuit is configured to operate with opposite polarity. ', Q6', Q1' are the fourth
Transistor Q in the figure. , Q6, and Q, and the circuit operations are completely the same except that the current polarity is opposite, so a description thereof will be omitted. The major difference from FIG. 4 is that the reference power source REF' is created based on the battery VBB, which has the advantage of increasing the degree of freedom in circuit design. Furthermore, in the circuit shown in FIG. 4, the on/off signal of transistor Q1 is converted to a TTL logic level. Although level conversion transistors Q3 and Q4 were required, the level conversion circuit shown in FIG. 5 is constructed using a diode O and a small number of resistors, thereby simplifying the circuit. As explained above, the ground fault detection according to the present invention does not require a high-precision high resistance, making it easy to implement into a semiconductor integrated circuit, and it is also possible to detect a ground fault even when a loop current is flowing. Furthermore, there is an effect that no special power source is required.

[Brief explanation of the drawing]

FIG. 1 is an example of a conventional ground fault detection circuit, FIG. 2 is a circuit diagram of a first embodiment of the ground fault detection circuit according to the present invention, and FIG. 3 is a circuit diagram of a second embodiment of the ground fault detection circuit according to the present invention. FIG. 4 is a circuit diagram of a third embodiment of the ground fault detection circuit according to the present invention, and FIG. 5 is a circuit diagram of a fourth embodiment of the ground fault detection circuit according to the present invention. show. Placement: Telephone, T: Transformer, VB
B...Battery, VOO, VEE...Power supply, Rl, vRE2t...Reference power supply, EO, EO'
, EON...Earth fault detection output, Ql9Q2FQ3
9Q49Q59Q69Q7PQ8? Q9...Transistor, D, d...Diode, RG, R
G'-...Ground fault resistance, RO, R,, RO', R1
TR! 0! R10'PRl! 9R12νR2OPR2O
to R2VR22lle●Resistance, R3OpR3O'? R3
lR322R33...Resistance.

Claims (1)

[Claims] 1 The battery line side is connected to the battery via at least one resistor, and the ground line side is connected to the ground via at least one resistor. Current is supplied from the current supply circuit to the terminal device via the battery line and the ground line. a first current-voltage conversion means for generating a voltage proportional to the battery line current using a preset reference voltage source as a reference;
a second current-voltage conversion means that generates a voltage proportional to the ground line current with respect to the ground; the output voltage of the first current-voltage conversion means is inputted to a first input; and a two-input voltage comparison means in which a voltage is applied to a second input, and when the battery line current becomes larger than the ground line current by a preset current value due to a ground fault in the battery line, the voltage comparison means A ground fault detection circuit characterized in that the output of the circuit is inverted.