JPH05130278A - Electronic choke circuit - Google Patents

Abstract

PURPOSE:To prevent a pulse width of a line signal from being made narrow by employing a diode biased forward as a generating element of a control voltage controlling a transistor(TR) interposed between choke terminals. CONSTITUTION:A TR interposed between choke terminals is operated in an active region with respect to a DC and even when an AC signal is superimposed onto the DC, the TR is controlled so as not to give effect onto a collector current of the TR. A diode D biased forward is employed for a control voltage generating element 1 to generate a control voltage controlling the TR. With a DC applied to the electronic choke circuit, a voltage VD across the diode D is inputted to a noninverting terminal of a differential amplifier circuit 20 and fed to a base of the TR in a voltage follower as a control voltage Vb. Captions R1, R2 are resistors. Since no capacitive element is employed in this circuit, the width of the line signal is not made narrow.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic choke circuit, and more particularly to an electronic choke circuit that does not use a capacitive element.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a relationship between a private branch exchange and a game, which is an example of a field to which the present invention is applicable.
In the figure, a switch SW of the private branch exchange PBX is connected to a central office exchange 6 (hereinafter referred to as a game) via a two-wire analog trunk circuit 2 and is connected to a telephone terminal T via a subscriber circuit 7. ..

FIG. 4 is a block diagram showing an outline of the two-wire analog trunk circuit 2 shown in FIG. A ringer detection circuit RD, a dial sending relay contact P, a choke circuit 3, and a loop current detection circuit LD are connected via a telephone line L connected to the game station 6. The AC component on the telephone line L, that is, the voice signal, passes through the capacitor C ₀ , the transformer TR, and the two-wire / four-wire conversion circuit 4 and is transmitted to the P of the private branch exchange.
It is housed in the exchange switch SW of the BX.

In the telephone exchange system as described above,
DC power is supplied from the exchange station to the subscribing terminal device for sending dial pulses, and also between stations, the same DC power is supplied from the local station (the receiving station) to the remote station (oscillating station). The DC power supply is performed through a line through which a call signal is transmitted. Therefore, as the choke circuit 3, a choke coil having a low impedance for direct current and a high impedance for alternating current (signal) has been used.

However, the choke coil is bulky, and the more the number of circuits is increased, the more serious the drawback thereof is. Therefore, an electronic choke circuit has been used as the choke circuit 3 in order to reduce its size.

FIG. 5 is a circuit diagram of a conventional electronic choke. A series circuit of a transistor Tr and a resistor R ₁ is connected between the choke terminals a and b, and the transistor T
The control voltage generating means 10 for r is also connected between the choke terminals a and b. This control voltage generating means 10
Chalk terminals a, min R ₃ / (R ₂ + R ₃₎ is a pressure comprised voltage of the resistor R ₂ and R ₃ are obtained from both ends of the resistor R ₃ when the DC is applied to b, it is superimposed further exchanges was the case, both ends of the resistor R ₃ are in a state of being short-circuited by the capacitor C ₁ connected in parallel with the resistor R _3, the voltage due to the application of the alternating current so as not to occur.

The control voltages V _b and υ _b generated by the control voltage generating means 10 are input to the base of the transistor Tr by a voltage follower via the positive terminal of the differential amplifier 20.

In this electronic choke circuit, the circuit operation at DC is as follows. That is, as described above, the capacitor C ₁ can be regarded as an open circuit with respect to direct current, so that the voltage V ₊ applied to the positive terminal of the differential amplifier 20 is increased.
Is

[0009]

[Equation 1]

Then, this voltage V ₊ is applied as it is to the base of the transistor Tr as the control voltage V _b . As a result, the current I flowing through the resistor R ₁ connected to the emitter side of the transistor Tr is

[0011]

[Equation 2]

Thus, the equivalent impedance Z _d of the electronic choke circuit for DC is

[0013]

[Equation 3]

[0014] As a result, the equivalent impedance Z _b of the electronic choke circuit with respect to direct current is equal to the resistance R ₁ ,
It can be understood that it is determined by R ₂ and R ₃ . On the other hand, the circuit operation under alternating current is as follows. That is,
Since the capacitor C ₁ can be regarded as a short circuit, the voltage υ applied to the positive terminal of the differential amplifier 20 by the alternating current component.
₊ Becomes υ ₊ = 0 (24), which is directly applied to the base of the transistor Tr as the control voltage υ _b . As a result, the resistance R ₁
The current i flowing in

[0015]

[Equation 4]

Therefore, the equivalent impedance Z _a of the electronic choke circuit with respect to alternating current is

[0017]

[Equation 5]

[0018] However, since the resistor R ₂ is actually seen through the capacitor C ₁ , Z _a = R ₂ (27)

Where R₁<< R₂Would be low in terms of direct current.
Impedance, high impedance in terms of AC,
It will have the same characteristics as the yoke coil. Shown above
The electronic choke circuit, as described in detail later,
Quantitative element (capacitor C₁) Is used, the time constant
R₂C₁Is it the place where the width of the dial pulse is narrowed by the influence of
, As shown in FIG. 6, an electronic circuit using a photocoupler.
Has also been developed. That is, as shown in FIG.
Resistance R of the generalized choke circuit ₂Photocoupler 2 between the terminals
1 transistor 21t is connected, and the photocoupler 21
The diode 21c returns a reverse response to the game.
Resistor R connected to the Ray driver 22 and the power supply Vcc_FourWhen
Connected between the time constant R₂C₁Dial due to
It is designed to prevent pulse deterioration.

According to this circuit, the relay driver 22 operates immediately in response to the dial pulse sent to the game 6, and the photocoupler 21 also operates accordingly, so that the resistance R
₂ is short-circuited, the capacitor C ₁ is charged rapidly, and deterioration of the dial pulse is prevented.

Further, the time constant R shown in FIG.₂C₁Impact of
The circuit shown in FIG. 7 has also been developed for the purpose of eliminating.
That is, the resistance R₂Zener diode D on both ends of_ZContact
The inrush current generated at each dial pulse
The above Zener diode D _ZShort-circuit the capacitor C
₁It is intended for quick charging of.

[0022]

As described above, the game 6 is played.
A line signal such as a dial pulse is sent from the PBX to the private branch exchange. Here, when a capacitive element (capacitor C ₁ ) is used as in the above circuit, the control voltage V _b rises gradually due to the time constant R ₂ C ₁ due to the capacitor C ₁ and the resistor R ₂ at the rise of the dial pulse, and the loop The rise of each pulse of the dial pulse train detected by the detection circuit LD (the rise of each dial pulse of the pulse train SCN) is only a value determined by the time constant R ₂ C ₁ from the closing time of the relay contact 5 (FIG. 8A). Delay (Fig. 8
(B)) Therefore, the pulse width of each pulse of the dial pulse train becomes narrow. Therefore, the narrower the original pulse is, the higher the narrowing rate is, and in an extreme case, the pulse cannot be detected, and the dial number is correct.
You will not be able to tell X.

Furthermore, the capacitor C ₁ used here not only has a large capacitance and therefore is bulky,
It cannot be incorporated in one IC, cannot be miniaturized, and has a short life of the capacitor, which causes maintenance problems.

The second conventional example was developed to compensate for the drawbacks of the first conventional example.
1 is inconvenient in that it can be realized for the first time under the control of the relay driver 22 and the like.

Further, the third conventional example is also developed to compensate for the drawbacks of the first conventional example, but a capacitor having a large capacity has to be used, a difficulty in miniaturization, and a short life. The difficulty is the same as the first conventional example.

The present invention has been proposed in view of the above conventional circumstances, and an object thereof is to provide an electronic choke circuit in which the pulse width of a line signal does not become narrow and which requires no special control. To do.

[0027]

The present invention employs the following means in order to achieve the above object. That is, as shown in FIG. 1, the transistor Tr interposed between the choke terminals a and b is operated in the active region with respect to direct current,
As a control voltage generating element 1 for generating a control voltage for controlling the transistor Tr in an electronic choke that controls so that the AC component does not affect the collector current of the transistor even when an AC is further superimposed, It uses a diode D biased in the forward direction.

[0028]

When a direct current is applied to the electronic choke circuit 3, the voltage V _D across the diode D is input to the positive terminal of the differential amplifier 20 as described above, and at the same time, the voltage follower causes a transistor. A control voltage _Vb is applied to the base of Tr. As a result, the current I flowing through the transistor Tr is

[0029]

[Equation 6]

If R ₁ << R ₂ , then the equivalent impedance Z _d of the computerized choke circuit 3 to DC is

[0031]

[Equation 7]

It becomes Next, for AC, an AC signal υ _in is further applied to both ends of the computerized choke circuit 3 on the DC V _in .

At this time, the diode D can be regarded as a short circuit in terms of AC, and the AC voltage υ _D across the diode becomes zero. As a result, the current i flowing in the electronic choke circuit 3 is

[0034]

[Equation 8]

It becomes Thus, the equivalent impedance Z _a for exchange of electronic choke circuit 3 is becomes infinite, the resistance R ₂ is to look through the diode D, the Z _a = R ₂ actually.

By setting R ₂ >> R ₁ ,
It is possible to obtain the electronic choke circuit 3 having a large impedance in terms of AC and a small impedance in terms of DC. Moreover, since the electronic choke does not use the capacitive element, the width of the line signal does not become narrow.

[0037]

FIG. 2 shows an example of a trunk circuit of a private branch exchange to which an electronic choke according to the present invention is applied.

A two-wire analog trunk circuit 2 to which the computerized choke circuit 3 according to the present invention is applied is connected to the game station 6. The signal received by the trunk circuit 2 is converted into four lines by the two-line / four-line switching circuit 4 and connected to the local network. A relay contact 5 for closing the loop is interposed in the preceding stage of the electronic choke circuit 3 of the present invention. The loop current detection circuit LD is omitted in the circuit of FIG.

The electronic choke circuit 3 is constructed as follows. That is, between the choke terminals a and b,
The transistor Tr and the resistor R ₁ are connected in series, and the control voltage generating means 10 formed of a series circuit of the resistor R ₂ and the forward diode D is connected.

The diode D operates as the control voltage generating element 1, the terminal voltage is input to the positive terminal of the differential amplifier 20, and the negative terminal of the differential amplifier 20 is connected to the emitter of the transistor Tr. As a result, the differential amplifier 20
Means that the voltage applied to the positive terminal is directly connected (by a voltage follower) to the base of the transistor Tr.

In the above configuration, when the relay contact 5 for closing the loop is closed and the DC voltage V _in of both terminals a and b is applied, the forward voltage is applied to the diode D. Then, the voltage V _D between both ends becomes a constant voltage (0.7 V in the case of a silicon diode).

The voltage V _D across the diode D is input to the positive terminal of the differential amplifier 20 as described above, and is also applied as the control voltage V _b to the base of the transistor Tr by the voltage follower.

V _D = V ₊ = V _b (11) As a result, the current I flowing through the transistor Tr is

[0044]

[Equation 9]

If R ₁ << R ₂ , then the equivalent impedance Z _d of the computerized choke circuit to DC is

[0046]

[Equation 10]

It becomes Next, for AC, an AC signal υ _in is further applied to both ends of the computerized choke circuit 3 on the DC V _in .

[0048] At this time, since the diode D is under the forward control voltage by the DC voltage V _in, the AC can be regarded as a short-circuit, therefore, the AC voltage upsilon _in
The AC voltage υ _D across the diode is zero due to the application of. Therefore, the applied voltage υ ₊ to the positive terminal of the differential amplifier 20
(Control voltage υ _b ) is υ _D = υ ₊ = υ _b = 0 (14).

As a result, the current i flowing in the electronic choke circuit is

[0050]

[Equation 11]

It becomes Thus, the equivalent impedance Z _a for exchange of electronic choke circuit 3,

[0052]

[Equation 12]

It becomes In reality, the resistor R ₂ is the diode D
Since it can be seen through, Z _a = R ₂ (17)

By setting R ₂ >> R ₁ ,
It is possible to obtain the electronic choke circuit 3 having a large impedance in terms of AC and a small impedance in terms of DC. Moreover, since the electronic choke does not use the capacitive element, the width of the line signal does not become narrow.

[0055]

As described above, the present invention realizes an electronic choke without using a capacitive element.
The width of the line signal is not narrowed, and the signal cannot be read or misrecognized. Further, since no capacitive element is used, all elements can be incorporated in the IC, downsizing is possible, and the circuit life is dramatically improved.

Further, since it is not necessary to control by a relay driver or the like, the circuit itself becomes simple.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a block diagram of a trunk circuit to which the present invention is applied.

FIG. 3 is a block diagram showing a relationship between a private branch exchange and a game.

FIG. 4 is a block diagram of an analog trunk.

FIG. 5 is a circuit diagram of a conventional electronic choke.

FIG. 6 is a circuit diagram of another conventional electronic choke.

FIG. 7 is a circuit diagram of another conventional electronic choke.

FIG. 8 is a conceptual diagram showing a delay of a line signal.

[Explanation of symbols]

 1 Control voltage generating element a, b Choke terminal D diode Tr transistor

Claims (1)

[Claims] 1. Even if a transistor (Tr) interposed between the choke terminals (a) and (b) is operated in an active region and an alternating current is further superimposed, the alternating current component affects the collector current of the transistor. A forward biased diode (D) was used as the control voltage generation element (1) for generating the control voltage for controlling the transistor (Tr) in the electronic choke circuit that controlled not to apply. Electronic choke circuit characterized by.