KR890000182Y1 - Loop current hipass circuit - Google Patents

Abstract

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Description

Telephone Line Loop Current Bypass Circuit Using Segmented Morse Field Effect Transistors and Control Diodes

1 is a DC loop current bypass circuit diagram of a conventional telephone line apparatus.

2 is a characteristic curve comparison of a telephone line loop current bypass circuit using a MOS field effect transistor and a zener diode and a conventional circuit.

Figure 3 is a specific circuit diagram of one embodiment according to the present invention.

* Explanation of symbols for main parts of the drawings

1: bridge rectifier using bridge diode

Q₂: Due to the moment-type MOS field effect transistor

R₄, R : Resistance ZD: Zener Diode

C₃, C₄, C Capacitor T

The present invention relates to a DC loop current bypass circuit in a telephone line connection device. A direct current loop current bypass circuit for separating a current from a direct current loop current.

Conventionally, in a telephone line connection device such as a private exchange, a resistance of R ₁ as shown in FIG. DC loop current bypass circuits consisting of (R₂) (R₃), Morse field effect transistor (Q₁) and capacitor (C₁) (C₂) have been used.

However, the first In Mohs since the voltage V _GS between the gate the source of the field effect transistor doeyeo a resistance divided by resistors R₁ and R₂ drain assist in the same circuit, the voltage thus between the gate the source as the source voltage V _GS increases between V _GS proportionally To increase.

Therefore, in the region where the DC loop current I _L is large, the loss of the negative current is rather large, and high frequency oscillation occurs when the resistance R₃ (source 8 term) connected to the source terminal of the MOS field effect transistor is increased to improve the constant current characteristics. There was a drawback that the value of the source resistance R₃ was limited.

Therefore, an object of the present invention is to provide a circuit that does not generate high frequency oscillation even when the source resistance R₃ is increased to improve the constant current characteristics, even though the loss of the negative current is very small even in the region where the DC loop current I _L is large.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

2 is a comparison of the characteristics of a conventional DC loop current bypass circuit using a moment-type MOS field effect transistor with the constant current characteristics of the circuit according to the present invention. It can be seen that the constant current characteristic is somewhat deteriorated in the region where the DC loop current I _L is large.

In addition, it can be seen that the curve of (b) shows excellent constant current characteristics even in a region where the DC loop current I _L is high as a characteristic curve of the inventive design.

3 is a circuit diagram embodying the above-described principle according to the present invention. Is the resistance, C₃, C₄, C ₅ is the capacitor, Q₂ is the cemented MOS field effect transistor, ZD is the zener diode, T is the transformer.

DC loop current (I _L ) input from telephone line (L₂) (L₂) is input to bridge rectifier (1) so that polarity is aligned and positive voltage (+) output from positive output terminal of bridge rectifier (1) ) Is input to the drain side of the MOS field effect transistor Q2 and to the cathode side of the resistor R 와 and zener diode ZD.

In addition, a source resistor R connected to the anode side of the zener diode ZD and the source terminal of the MOS field effect transistor Q2 is connected to a negative voltage (−) output from the negative output terminal of the bridge rectifier 1. To be entered.

On the other hand, the divided voltage by the resistor R 'and zener diode ZD is input to the gate of the MOS field effect transistor Q2. A capacitor C 접속 for bypassing the AC negative current is connected to the gate of the MOS field effect transistor Q₂, and an AC audio signal is coupled to the primary side of the transformer T by the capacitor C ₃ . A high frequency oscillation preventing capacitor C ₅ capable of preventing high frequency oscillation is connected between the gate and the drain of the MOS field effect transistor Q 2.

Now the voltage between the drain source of the MOS field effect transistor Q₂ is V _DS , the drain current I _D , the drain current I _D , the drain current I _D If the voltage drop generated by V _RS is V _RS , the terminal voltage V 간의 between the positive and negative output terminals of the rectifier circuit 1 is expressed by the following equation.

V₁ = V _DS + I _D R _5. ................. (1)

The source resistance R in the formula (1) Assuming that the voltage drop by V _RS is as follows.

V _{R5 =} I _{DR 5} ... (2)

In addition, since the gate voltage V _GS of the MOS transistor Q₂ is equal to the voltage applied to the zener diode ZD minus the voltage drop V _R5 of the source resistor R ₅ , the DC resistance of the zener diode ZD is represented by R _ZD . Can be written as

Therefore, since the AC terminal signal is superimposed on the DC loop current at the output terminal voltage V 의 of the rectifier circuit 1, as shown in Equation (3), the AC voice signal is also loaded on the voltage V _GS between the gate and the source. Since it can be input to the gate of the), it is possible to bypass the voice exchange signal component using a capacitor (C₄).

Therefore, when the capacitor (C₄) is connected, the AC voice signal contained in the voltage V _GS between the gate sources is bypassed through the capacitor (C₄), so that only a constant DC voltage is input to the gate of the MOS field effect transistor (Q₂).

Therefore, the current I _DS between the drain sources becomes constant. In addition, as the DC loop current I _L increases, the TJ drain current I _D also increases, and the voltage increase of the source resistance R ₅ increases with the flow of the drain current I _D.

Therefore, the voltage V _GS between the source and the gate, as can be seen in formula (3) with the increase of the drain current I _D, and decreases the voltage V _GS between the gate sources is possible to suppress the increase of the drain current I _D.

On the other hand a capacitor (C ₅₎ the increase in the source resistor R ₅ in order to improve the constant current characteristics of the circuit if not because of the feedback between the gate and the source of the Mohs field effect transistor (Q₂) is a high-frequency oscillation up, because capacitor (C ₅₎ Is connected between the gate terminal and the source terminal of the MOS field effect transistor Q2, thereby preventing high frequency oscillation by preventing feedback between the gate and the source of the MOS field effect transistor Q2.

Therefore, by connecting the high frequency oscillation preventing capacitor C ₅ , the source resistance R ₅ can be set to a large value in order to improve the constant current characteristic of the circuit.

The voltage inputted to the gate terminal of the MOS field effect transistor Q₂ is inputted by dividing the output terminal voltage V₁ (voltage of the drain source V _DS ) of the bridge rectifier 1 by the resistor R₄ and the zener diode (ZD). In the case of the resistance partial voltage, the voltage V _GS between the gate sources increases proportionally according to the voltage V _DS between the drain sources. When the DC loop current I _L is large, the constant current characteristics of the circuit deteriorate and there is a loss of the voice current.

However, in general, the zener diode has a characteristic of decreasing the direct current resistance of the zener diode as it approaches the zener voltage. Therefore, the output terminal voltage V₁ (voltage V _DS between the drain sources) of the bridge rectifier 1 is used by using this characteristic. When the divided voltage divided by the DC resistance R _ZD of R ₄ and zener diode (ZD) is input to the gate of the MOS field effect transistor (Q₂), the loop current I _L increases to increase the voltage V _DS between the drain source (bridge rectifier (1) ) Even if the output terminal voltage V₁) increases, the DC resistance R _ZD of the zener diode _ZD is relatively low, and thus the voltage division ratio with the resistor R₄ decreases, which may be input to the gate terminal of the MOS field effect transistor Q₂. .

Therefore, excellent constant current characteristics can be obtained even in a region where the DC loop current I _L is high.

As described above, the present invention inputs a voltage obtained by dividing the input voltage of the gate of the Morse field effect transistor using the DC resistance characteristic of the Zener diode to control the drain current I _D even in a region where the DC loop current I _L is high. Impedances can also be extremely high compared to conventional circuits.

On the other hand, high frequency oscillation has occurred as the source resistance is increased to improve the constant current characteristics, but the source resistor is prevented by connecting the capacitor (C ₅ ) between the gate terminal and the source terminal of the MOS field effect transistor (Q₂) to prevent high frequency oscillation. Can be taken at a high value.

Therefore, it has a stable constant current characteristic in the long region of the loop current, so that most of the negative current superimposed on the loop current can be separated by a transformer through the capacitor C₃.

Claims (1)

In a circuit for separating the DC loop current I _L and the voice AC signal current according to a telephone line connection device, a voltage dividing furnace (R₄) for inputting a DC loop current output from the output terminal of the rectifier circuit 1 to perform voltage division. A capacitor (C 된) connected in parallel with the zener diode (ZD) for bypassing the (ZD) and the minute audio exchange signal component input to the voltage divider circuit, and a voltage divided by the voltage divider circuit to be input to the gate. A gate-type source field transistor (Q2) and a gate terminal of the source field effect transistor (Q₂) and a source type source field effect transistor (Q₂) caused by a DC loop current flowed by a gate-source voltage by connecting a source resistor (R ₅ ) to a terminal. Bypass the negative AC signal current between the capacitor (C ₅ ) and the drain and the transformer (T) primary side connected between terminals to prevent high frequency oscillation. DC loop current bypass circuit comprising a capacitor (C₃).