JPS61224767A - Feeding circuit - Google Patents

Abstract

PURPOSE:To omit the crosstalk countermeasure which is small-sized, light, at a low cost and between lines by providing a feeding control part and an active low-pass filter which turn ON and OFF the connection of a line voltage detecting resistance and a feeding line. CONSTITUTION:When the pulse of an on/off signal is inputted through a feeding control part 13 to an active low-pass filter part 12, a harmful click component out of the respective even number higher harmonic components is removed from the basic wave to constitute the pulse of an on/off signal. When the cut-off frequency is set to the sufficiently low frequency, the output is shaped to the waveform of the smooth change even when the sharp waveform is inputted for both the rise and the fall at a filter part 12. Further, by a feeding circuit part 11, the electric current of the same waveform as the waveform is supplied to the line. By constitution also the electric power source noise so as to make the output of the filter 12 into the constant electric current control voltage of the circuit part 11, the genaration is prevented. Thus, the crosstalk counter measure is unnecesary which is small-sized, light, at a low cost and between lines.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a communication current supply circuit connected to a communication path of a telephone exchange network, and in particular to a circuit for supplying current from an incoming trunk of an exchange to an outgoing trunk of a partner station. Regarding the supply circuit.

[Conventional technology]

As shown in the block diagram of FIG. 5, the conventional incoming trunk power supply circuit, which is in danger of relaying billing pulses, consists of a power supply circuit section 51 using a communication power source, and a power supply control section 52 that controls the on/off of the power supply circuit section 510. , and a low-pass filter section 58 that suppresses the occurrence of click noise on the line during billing pulse relay.

FIG. 6 is a diagram showing a specific example of this conventional circuit.

The choke coil L and the capacitors CO to C3 constitute a low-pass filter section 58, and the relays T and S contacts t and 8 (not shown) and the resistor R constitute a power supply control section 52, and power is supplied by the operation/restoration of the contact S. Control takes place. The power supply circuit section 51 is composed of a relay W having low DC resistance and high AC impedance characteristics. Note that the contact point t is a contact point for sending out a response reverse signal, and is a contact point that sends a response from a subsequent stage as a reverse signal to the relay line. Also,
The contact e operates normally and instantaneously recovers when it sends out a loop breaking pulse (usually about 100 to 200 mg) as a billing pulse signal. Resistor R is connected so that even if contact e is restored at this time, relay W continues to operate.

[Problem that the invention seeks to solve]

As mentioned above, when relaying billing pulses, the conventional power supply circuit uses a choke coil L and a capacitor CO to prevent click noise caused by billing pulses to the subscriber side.
A low-pass filter section 5B based on C3 is provided.

Since the choke coil L constituting this filter requires high inductance and direct current superposition, it has the following drawbacks.

■ The shape is large and the space 7 actor is bad. ■ The choke coil must be unbalanced and shielded to prevent crosstalk between lines. ■ It is heavy and the mounting method is limited. ■ It is expensive.

In addition, capacitors CO to C3 are large in size, heavy, and expensive because: ■ They require relatively large capacitance because they have a low passband. ■ They require high withstand voltage because they are connected to the line. It has some drawbacks.

Furthermore, the conventional circuit has a power supply control section 52 and a power supply circuit section 5.
The noise generated in step 1 is suppressed by a low-pass filter section 58 before being output to the line, and has a major drawback in that it does not reduce the generated noise itself.

SUMMARY OF THE INVENTION An object of the present invention is to provide an unnecessary power supply circuit that is small, lightweight, low cost, and prevents crosstalk between lines.

[Means for solving problems]

The present invention provides a power supply control unit that connects and disconnects a detection resistor that detects line voltage and a power supply line, an active low-pass filter unit that receives the output voltage of the detection resistor, and an output of the active low-pass filter unit. The power supply circuit has a power supply circuit unit that outputs a constant current using the control voltage as a control voltage, and has a configuration in which the output of the power supply circuit unit is connected to a power supply line.

Furthermore, the capacitor for the active low-pass filter is connected to a communication power supply, and the circuit has a circuit configuration such that noise from the power supply is sufficiently applied to the constant current control voltage of the power supply circuit through this capacitor.

〔Example〕

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

FIG. 1 is a block diagram showing an embodiment of the power supply circuit of the present invention. In this embodiment, a power supply circuit section 11 having constant current characteristics is used.
, an active low-pass filter section 12, and a power supply control section 18 that performs on/off control and the like.

Figure 2 shows a specific example of the circuit on the A-line side of Figure 1, and the B-line side is completely identical except for the polarity of the stone transistors used. Since the above is the same, I will omit it. In the figure, the power supply control section 18 is controlled by resistors RO to R2 and transistors Qo to Q2, and resistors R5 and R6.
, capacitors Co, C1, and operational amplifier ICt, the active low-pass filter section 12 is connected to resistors R7, R11,
The power supply circuit section 11 is constituted by a well-known constant current circuit including an operational amplifier ICg and a transistor Q3. Note that the operational amplifier ICo is a buffer using a well-known voltage regulator, and the resistors R3 and R14 are line voltage detection resistors for realizing constant resistance power supply to the power supply circuit section 11.

Next, detailed operation of the circuit shown in FIG. 2 will be explained below. FIG. 8 shows the on/off signal supplied to the power supply control unit 18 and the current control voltage input waveform of the power supply circuit unit 11.

When the on/off signal is at a low level as at time 11, a predetermined pace current flows through the transistor Q through the resistor Ro.
o, transistor QO is turned on in the switching operation region υ, and transistors Q1 . Q2 is turned on. When the transistor Q2 turns on, the relay line resistance and the resistance Ra.

A voltage determined by R4 is applied to the emitter of transistor Q2. Further, the voltage divided by the line voltage detection resistors Ra and R14 is directly transmitted to the non-inverting input terminal of the operational amplifier ICz, which is a constant current circuit, via the operational amplifiers ICo and ICt. The operational amplifier IC2 compares the outputs of the non-inverting input terminal and the inverting input terminal, and performs a well-known constant current operation so that both input voltages become equal.

The DC operation is as described above, but the operation in the transient state at the rise or fall of the on/off signal will be explained below at time 1. When the pulse of the on/off signal is input to the , the output of the operational amplifier ICo is similar to DC operation, but when this output is input to the active low-pass filter section 12, the pulse of the on/off signal Among the even-order harmonic components, harmful click components are removed from the fundamental wave constituting the . If this cutoff frequency is set to a sufficiently low value, for example, about 29 Hz, even if a waveform with sharp rises and falls is input to the active low-pass filter section 12, the output will be shaped into a waveform with smooth changes. A current having the same smooth waveform as this smooth waveform is supplied to the line by the power supply circuit section 11 composed of the operational amplifier IC2 as shown in FIG.

In this way, the DC current changes smoothly and generates noise. Moreover, since the active low-pass filter section IS blocks the audio band signal from the audio signal superimposed on the DC current, the power supply circuit section 11 obtains an AC high impedance characteristic.

Furthermore, the power supply noise attenuation characteristic, which is the second characteristic of the present invention, will be explained.

A capacitor CI constituting the active low-pass filter section 12 shown in FIG. 2 is connected to a line current supply power source -48. Therefore, when this power supply -48VFC noise is superimposed, the power supply noise is often superimposed on the output of the active low-pass filter section 12 through the capacitor C1. On the other hand, this power supply noise is also applied to the current change detection resistor R8 of the power supply circuit section 11, and the same power supply noise is applied to the non-inverting and inverting input terminals of the constant current control operational amplifier ICz. If the capacitance of the capacitor CI is sufficiently large and enough power supply noise can be added, the power supply noise will be canceled in the operational amplifier IC2, and the output transistor Q of the power supply circuit section 11 will be
No power supply noise is output to the collector No. 3.

FIG. 4 is a circuit diagram showing another embodiment for explaining power supply noise attenuation characteristics, in which a resistor Ro-R2 is used.

Transistors QO to Q2 control power supply control unit 1 for communication current.
8 is an operational amplifier ICo, a resistor R11, and a transistor Q5.
O constitutes a first-order low-pass filter. Here, resistors Rs and Rs represent line voltage detection resistances. That is, compared to FIG. 2, the active low-pass filter section 12
The difference is that is a first-order low-pass filter. If the power supply noise from the -48V power supply is applied to the non-inverting input terminal of the operational amplifier ICo as a constant current control input voltage of the power supply circuit section 11 by the capacitor Co shown in FIG. 4, it is similar to the removal of the click component in FIG. Thus, no power supply noise is output to the collector of transistor Q5 in FIG.

In the above explanation of FIG. 4, the power supply circuit that supplies the A line has been explained.
,R11! , ) transistor Q31Q'IQ' m
This is a circuit that supplies the operational amplifier ICt and the capacitor CttiB line, and the operation is the same except that the polarity of the current is opposite to the A line side, so a detailed explanation will be omitted.

In addition, if +50V is required as a power supply to the line, cut off the connection between the J-G terminals shown in the gX4 diagram, and
- Make the connection between the BB terminals. In this case, the noise levels of -48V power supply noise and +50V power supply noise are different.
As shown in this embodiment, mutual interference of power supply noise between the A line side and the B line side can be suppressed by blocking the A line side and the B line side individually.

〔Effect of the invention〕

As explained above, the present invention provides a power supply control unit that turns on/off the connection between a line voltage detection resistor and a power supply line, an active low-pass filter unit that receives the detected voltage as input, and furthermore, the active low-pass filter By configuring the output of the section to be the constant current control voltage of the power supply circuit section,
A power supply circuit with high AC impedance and low DC resistance can be obtained without generating noise on the line when the power supply current is turned on and off, and the circuit configuration can be made entirely of electronic circuit components, making it extremely compact and economical. It is possible to realize space savings, weight reduction, and cost reduction. Further, since the present invention does not include any inductance, it can achieve a large resistance to crosstalk with other lines, and has the feature of fundamentally solving the drawbacks of conventional power supply circuits using electromagnetic components.

[Brief explanation of the drawing]

Fig. rA1 is a block diagram of an embodiment of the present invention, Fig. 2 is a specific circuit diagram of the embodiment, Fig. 8 is a timing chart showing the operation of the embodiment, and Fig. 4 shows power supply noise attenuation characteristics by a capacitor. FIG. 5 is a block diagram of a conventional example, and FIG. 6 is a circuit diagram of a conventional example. 11...Power supply circuit section 12...Active low-pass filter section 18...Power supply control section Patent applicant NEC Corporation Fig. 3 Fig. 5

Claims (1)

[Scope of Claims] A power supply circuit that supplies communication current in a telephone exchange network, which inputs a line voltage detection resistor and a control signal, and controls connection/disconnection of the detection resistor and the power supply line according to the level thereof. an active low-pass filter that receives the output voltage from the detection resistor as an input; and a power supply control unit having a control means for controlling the output voltage of the active low-pass filter; A power feeding circuit comprising: a power feeding circuit section that outputs to the power feeding line.