JPH0365860A - Speech current limit circuit - Google Patents

Abstract

PURPOSE:To eliminate the need for a large capacity capacitor and to reduce the cost by causing a current of each Zener diode to flow through a resistor interconnecting bases of transistors(TRs). CONSTITUTION:A base voltage made constant by Zener diodes 5, 5', a collector output of PNP TRs 4, 4' at a high potential side having a constant current circuit using an emitter resistor, a base voltage made constant by other Zener diodes, and a collector output of NPN TRs 4, 4' at a low potential side having a constant current circuit using an emitter resistor are used for a voltage supplied to a tip terminal 2 and a ring terminal 3 of a telephone subscriber circuit in a PBX. Then the current of each Zener diode flows through resistors 7, 7' interconnecting bases of the TRs. In this case, since the current flowing to the Zener diodes does not flow to a line between the tip terminal and the ring terminal, the impedance when viewing the TRs from a telephone set depends only on the collector. Thus, a large capacitance capacitor is not required.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a speech current limiting circuit for an analog telephone connected to a subscriber circuit such as a PBX.

(Prior Art) Fig. 2 shows a call current limiting circuit connected to a telephone subscriber circuit of a conventional PBX, in which 1 is an analog signal telephone connected between a tip terminal 2 and a ring terminal 3. .

4 and 4' are PNP transistor and NPN transistor, respectively.
Transistor, 5°5' is Zener diode, 6,6
' is the capacitor, 7.7' is the emitter resistance (resistance value is r
8°8' are transistors 4 and 4, respectively.
′ base bias resistance (resistance value is r2), V
□, V2 is the power supply, and V>V.

When the telephone 1 is connected to the subscriber circuit as shown in the figure, the Zener diodes 5 and 5' have (V2)/2
r2 [Al current flows, and a Zener voltage of V, [vl is generated. The base-emitter voltage V1g of each of the transistors 4 and 4' is V, Ii20,
7 [V': Because it is kept constant.

Emitter resistors 7 and 7' are always (V - 0.7) [V
] is applied (V z O, 7) / r 1 [
Al current flows.

In this state, the impedance seen from the telephone l toward the tip terminal 2 or ring terminal 3 is r, 1 h1. r1(h
4. : alternating current amplification factor of transistors 4, 4'), but in general, l'lfe varies widely, and the impedance on the chip terminal 2 side and the ring terminal 3 side is different.
This results in deterioration of the longitudinal balance characteristics.

To improve this, a capacitor 6.6' is connected between the base of each transistor 4, 4' and the power supply V□ or V2, and the impedance h when looking at the chip terminal 2 and ring terminal 3 sides from the phone 1 is 4* r t
This reduces the impact of

(Problem to be Solved by the Invention) However, improving the vertical balance by connecting capacitors as described above requires a capacitor with a large capacity, thus increasing the mounting area and increasing costs. .

(Means for Solving the Problems) The present invention achieves the above object by changing the voltage supplied to the tip terminal and the ring terminal of the telephone subscriber circuit in a PBX by using a base voltage constant by a Zener diode and a constant voltage by an emitter resistor. P on the high potential side with a current circuit
The configuration is such that the collector output of the NP type transistor, the base voltage kept constant by another Zener diode, and the collector output of the low potential side NPN type transistor having a constant current circuit using an emitter resistor are used to supply each of the above. The Zener diode current is achieved by flowing through a resistor whose bases are connected to each other.

(Function) According to the present invention, since the current flowing through the Zener diode is not passed between the chip terminal and the ring terminal, the impedance seen from the telephone to the transistor side is determined only by the collector, and therefore the vertical balance is improved. A large capacitance capacitor is not required, which reduces the mounting area and reduces costs.

(Example) Hereinafter, the present invention will be explained using the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.
9 is a resistor (resistance value is r); other symbols are the same as the corresponding symbols in FIG. 2, or have equivalent functions and operate in the same way.

The resistor 9 mentioned above connects the bases of the transistors 4 and 4'.

Zener diodes 5 and 5' each have (V□ V
22V, r/r-[A current flows constantly, V, [vl
Zener voltage is generated. Transistor 4, 4'
The base-emitter voltage VIIg of is approximately 0.7 [
V], while the resistance 7°7' is always
A voltage of -0.7 [V] is applied (V 2 0.7)
/ r, [A] current flows through the telephone l, so that at all times ■″F(VZ 0.7)/r-[A]
Electrician flows.

In the circuit configured as above, the impedance when looking from the phone 1 to the chip terminal 2 side or the ring terminal 3 side is:
Only the collectors of the transistors 4 and 4' each have impedance, resulting in a high impedance, resulting in a communication current limiting circuit with good longitudinal balance characteristics.

(Effects of the Invention) As is clear from the above explanation, the present invention improves the vertical balance characteristics and can reduce the number of resistor and capacitor components, resulting in a reduction in mounting area and cost. can get.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a telephone subscriber circuit according to an embodiment of the present invention;
FIG. 2 is a diagram showing a conventional PBX telephone subscriber circuit. l...telephone, 2...chip terminal, 3...
・Ring terminal, 4,4'...transistor,
5,5''...Zener diode. 6.6'...Capacitor, 7,7'...Emitter resistance, 8.8'...Bias resistor, 9...
resistance.

Claims (1)

[Claims] The voltage supplied to the chip terminal and ring terminal of the telephone subscriber circuit in the PBX is made constant by a base voltage using a Zener diode, and the collector output of a PNP type transistor on the high potential side having a constant current circuit using an emitter resistor; The base voltage is kept constant by another Zener diode, and the collector output of a low-potential NPN transistor having a constant current circuit using an emitter resistor is used to supply the current. A call current limiting circuit characterized in that the current is passed through a resistor whose bases are connected together.