JPS6251548B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a line current supply circuit used for supplying line current from an exchange to various terminal devices such as telephones.

The subscriber circuit of an exchange to which terminal equipment that requires line current supply is connected has line current supply (Battery feed.), overvoltage protection (Over voltage protection)
functions such as protection.), ringing signal transmission (Ringing.), monitoring (Supervision), 2-wire 4-wire conversion (Hybrid.), testing (Test), and encoding (Coding.). Although it is called the BORSCHT function, most of it is implemented in the trunk circuit of the exchange.

On the other hand, with the progress of integrated circuit technology, the digitization of communication channels has become a reality, and for toll switching systems, "Research and Practical Report Vol. 28, No. 7, Digital Telephone Toll System DTS-1 Special Feature" ( Although it has been put into practical use as shown in the publication (published by Nippon Telegraph and Telephone Public Corporation and Musashino Telecommunications Research Institute), it is not possible to transmit large-amplitude signals to subscriber switching systems through digital communication paths. ,
It is necessary to provide the BORSCHT function in the communication path, and there is a particular demand for miniaturization and cost reduction of subscriber circuits.

Therefore, the conventional configuration, which mainly consists of electromagnetic components such as blocking wires called letter coils or relays, cannot achieve the purpose, and it is essential to integrate the subscriber circuit. For example,
“IEICE Technical Research Report” vol1.79, No.34,
As stated in ``A Consideration of Call Current Supply System'' published by SE79-20 (published by the Institute of Electronics and Communication Engineers), a few studies have been carried out.

However, simply replacing the function of the letter coil with an electronic circuit will result in a large power loss in the line current supply circuit due to the supply of line current, and heat dissipation will become an issue when integrating the circuit. , solving these problems is considered to be an urgent task at present.

In other words, Figure 1 shows the equivalent circuit of the line current supply system when a letter coil is used.
The internal resistance of TE is R _T , the line resistance of lines L ₁ and L ₂ is R _L , the DC resistance of letter coil LT is R _S , power supply B
If the voltage at is E, the line current I _L is expressed by the following equation.

I _L = E/R _T + R _L + R _S ... (1) Also, the power loss P _S in the letter coil LT is P _S = R _S・I _L ² = R _S / (R _T + R _L + R _S ) ²・E ²
...(2), and when the line resistance R _L is zero, P _S is maximum.

Therefore, if the maximum value of P _S is Psmax, then Psmax = R _S / (R _T + R _S ) ²・E ² ...(3), _RT = 50Ω, R _S = 440Ω, E = 48V Then, Psmax=4.2W, which is completely unacceptable for integrated circuits.

The present invention satisfies such conventional demands and has the purpose of fundamentally solving the conventional problems, and by supplying constant power to the line on the track side, the power in the line current supply circuit is reduced. The object of the present invention is to provide a line current supply circuit that minimizes loss and is extremely easy to integrate.

The details of the present invention will be explained below with reference to FIG. 2 and subsequent figures showing embodiments, but first, the preconditions and principle of the present invention will be explained.

In other words, the conventional line current supply characteristics are determined by equation (1), and the terminal equipment TE operates according to the line current supply characteristics of equation (1). , it is sufficient to guarantee the minimum current in the conventional line current supply characteristics.

Also, if we focus on the AC signals sent and received in the terminal equipment TE, for example, in the case of voice signals from a telephone, the voice signals are transmitted via the lines L ₁ and L ₂ , so
The amount of loss is determined according to the line length, and in order to prevent excessive sound volume when the line length is short, the terminal equipment TE
The volume is adjusted on the side.

For this volume adjustment, please refer to the 7th research practical application report.
As described in Volume 6, No. 6 (published by Nippon Telegraph and Telephone Public Corporation, Musashino Telecommunications Research Institute), pages 1189 to 1204, "601 type telephone circuit network," some models automate volume control, and in this case, Since the line current varies depending on the line length, the line current is used as control information for volume adjustment.

Therefore, as for line current supply characteristics, by satisfying the following conditions, a sufficient line current can be supplied to most terminal devices TE.

(A) Internal resistance R _T of terminal equipment TE and line resistance R
Within the allowable variation range of _L , a line current greater than a predetermined minimum value is supplied.

(B) In the "region of small line resistance" including the terminal device TE and the lines L ₁ and L ₂ , a line current is supplied that approximates the line current supply characteristic given by equation (1).

Note that the "region of low line resistance" in item (B) is not necessarily determined depending on the configuration of the terminal equipment TE, but in conventional telephones, the line loss of approximately 3 dB is the limit for inserting a resistive attenuator for volume adjustment. , and line loss of 3 dB or less can be considered a "region of low line resistance."

In addition, "Research and Practical Application Report" Volume 12, No. 12 (published by Nippon Telegraph and Telephone Public Corporation, Musashino Telecommunications Research Institute)
According to P1475-1632 "600 type telephone", the resistance attenuator for volume adjustment has line loss of 0.5mmφ cable.
It corresponds to 3dB, and its resistance value is 300Ω.According to the above-mentioned “601 type telephone circuit network,” the direct current resistance of the telephone is around 80Ω. includes a slight margin
It becomes clear that it is sufficient to consider the resistance to be around 500Ω.

FIG. 2 is a circuit diagram showing the principle of the present invention based on the above premise. The line current supply circuit (hereinafter referred to as supply circuit) LCF includes a power transfer circuit (hereinafter referred to as supply circuit) that transfers a certain amount of power to the line side. transfer circuit) PTF,
Voltage drop element DE inserted in series to its output side
and the transfer circuit PTF is connected to the transformer T
is inserted in series with the primary winding T _P of the transformer T,
It is comprised of a switch S, which performs on/off operations at predetermined cycles in response to a control signal from a control terminal CT, a diode D, and a capacitor C.

Furthermore, the polarity relationship between the primary winding T _P and the secondary winding T _S of the transformer T is shown by dots, and when the switch S is turned on, the power input from the power supply B is turned on. When applied to the secondary winding T _P , a positive electrode is generated on the diode D side of the secondary winding T _S. At this time, since the diode D is inserted in series in the non-conducting direction, the secondary winding T No current can pass through _S , and the primary winding T _P of the transformer T acts as an inductance, and power is stored there as electromagnetic energy.

Here, the inductance of the primary winding T _P is L,
The on time of switch S is t _po and the voltage of power supply B is E
Then, the power P _C stored in the transformer T is given by the following equation.

P _C = 1/2L・E ²・t _po ² ...(4) This power P _C is the result of the induced voltage in the secondary winding T _S in the forward direction with respect to the diode D when the switch S is turned off. Therefore, it is discharged to the capacitor C side and flows through the lines L ₁ , L ₂ , the terminal equipment TE and the voltage drop element DE, thereby reducing the line current I _L
is supplied.

Note that the ripple component of the line current I _L is removed by the action of the capacitor C, and the line current I L flows as a direct current.

Furthermore, if the frequency of the cycle in which the switch S turns on and off is f, then the power Pout transferred to the output side of the transfer circuit PTF per second is expressed by the following equation.

Pout=1/2L·E ² ·t _po ² ·f (5) Therefore, if the frequency f is constant, a constant power Pout is always transferred to the output side.

Note that if the off time of switch S is t _pff , then the relationship f=1/(t _po +t _pff )...(6) holds, so equation (5) can also be expressed by the following equation. can.

Pout=1/2L・E ₂・t _po ²・1/to _o +t _pff ...
…(7) On the other hand, the line current I _L is the line resistance R _L , the terminal equipment
Power consumed by internal resistance R _T of TE and voltage drop element DE, and transfer power of transfer circuit PTF
Pout is equal, so if the voltage drop due to the voltage drop element DE is Vde, the following formula holds true, I _L ²・(R _T +R _L )+I _L・Vde=Pout...(8) Voltage drop element Since DE is composed of a value series connection of a constant voltage diode exhibiting a constant voltage component and a resistor r exhibiting a resistance component, the voltage drop Vde
, the constant voltage V _Z caused by the constant voltage diode ZD and the terminal voltage I of the resistor r generated by the line current I _L
By combining with _L ·r, it is expressed as Vde=V _Z +I _L ·r, and by solving for the line current I _L , the line current I _L is expressed by the following equation.

FIG. 3 shows the line current supply characteristics when using the conventional letter coil LT by the broken line, and the line current supply characteristics of the present invention based on equation (9) by the solid line. The supply characteristics of the present invention are as follows: the DC resistance of the letter coil LT is 440Ω, the power supply voltage E is 48V, and the supply characteristics of the present invention are that the transfer power Pout is 1.7W,
The resistor r of the voltage drop element DE is 25Ω, the constant voltage diode constant voltage V _Z is 7V, and the horizontal axis shows the terminals.
The line resistance R seen from t ₁ and t ₂ to the lines L ₁ and L ₂ is plotted, and the line current I _L is plotted on the vertical axis.

The dashed-dotted line is the supply characteristic for a ±15% deviation in DC resistance R _S of the conventional letter coil LT, which is converted into the DC resistance change of the letter coil LT based on the copper wire temperature coefficient of 4.3 x 10 ^-3 /°C. This corresponds to a temperature change of about 35°C, which is within the generally accepted range.

Therefore, as shown in FIG. 3, it is clear that the supply characteristics according to the present invention are within the allowable range of conventional supply characteristics and are sufficient for practical use, provided that the line resistance R is 800Ω or less.

FIG. 4 shows the power loss characteristics with line resistance R plotted on the horizontal axis and power loss P _L in the supply circuit LCF plotted on the vertical axis. It shows the power loss P _L in the circuit.

However, the power loss P _L in the supply circuit of the present invention shown in FIG. 4 is 1.7W/0.85=2W
Since it includes a fixed difference from the output power, that is, a loss of 0.3W due to power transfer efficiency,
The amount of change in power loss P _L with respect to the change in line resistance R appears to be very small.

To explain this further, in an area where the line current is large, that is, an area where the line resistance R is small, the voltage drop due to the resistor r of the voltage drop element ED is large, and power loss also occurs in the resistor r. In a large area, the voltage drop across resistor r is small and the power loss due to this is also reduced, and the voltage drop element
The dominant term is the power loss proportional to the line current due to the constant voltage component of the ED.

Note that in the supply circuit of the present invention, the transfer circuit PTF
Assuming a power transfer efficiency of 85%, the same circuit
Power losses within the PTF are also included.

That is, as shown in the figure, the line resistance R
When _L is zero, only the internal resistance R _T of the terminal equipment TE appears as the line resistance R, which is generally about 50Ω, so in a conventional supply circuit, the power loss P _L is about
In contrast, according to the supply circuit of the present invention, the power loss P _L is approximately 1 W, which is sufficiently permissible in integrated circuits of general shapes. integrated circuits will be realized.

Note that the power loss R _L1 in the supply circuit LCF of the present invention, excluding the loss associated with power transfer, mainly occurs in the voltage drop element DE, and its value is expressed by the following equation.

P _L1 = I _L ²・r+I _L・V _Z ...(10) On the other hand, the power loss P _L2 in the conventional supply circuit
is generated by the DC resistance R _S of the letter coil LT, and its value is expressed by the following equation.

P _L2 = I _L ²・R _S ...(11) Therefore, if we take the ratio of both, P _L1 /P _L2 ≒r/R _S +V _Z /I _L・R _S ...(12) Therefore, , if compared under the conditions shown in Figure 3, r=25
Ω, V _Z =7V, R _S =440Ω, and I _L =100mA.
Then, P _L1 /P _L2 =50/440, and according to the present invention, the power loss is reduced to about 1/9 compared to the conventional case, assuming that the efficiency of the transfer circuit PTF is 100%.

In addition, the voltage drop element DE has the function of approximating the line current supply characteristics to the conventional one, as well as the function of the transformer T.
It also has the effect of preventing saturation.

That is, before the power stored in the transformer T is completely released, power is stored, and as a result of this repetition, if more power than the transformer T can store is stored in the transformer T, the transformer T To prevent this, the terminal voltage of capacitor C, E _C
must be maintained above a predetermined value, but
Even if there is a short circuit between L ₁ and L ₂ due to a fault, etc., by inserting the voltage drop element DE, By maintaining the voltage E _C as the terminal voltage E C of the capacitor C, saturation of the transformer T is prevented.

Note that approximately the same effect can be obtained even when a simple resistor is used as the voltage drop element ED. However, if only a resistor is used, the line current supply characteristic, that is, the line resistance R based on the internal resistance R _T of the terminal device TE and the line resistance R _L
The relative relationship of the line current I _L to the voltage drop element ED is uniquely determined by the value of the resistor used as the voltage drop element ED. It becomes difficult to approximate everything within the range.

Therefore, in the present invention, by using a constant voltage element that generates a power loss proportional to the flowing line current as the voltage drop element ED, the line current can be reduced by 2.
It compensates for line current supply characteristics that are different from resistors, which cause power loss proportional to the Improved approximation accuracy for characteristics has been achieved.

FIG. 5 is a circuit diagram showing an embodiment of the present invention, in which a field effect transistor (hereinafter referred to as FET) Q is used as the switch S, and an oscillator OSC that generates a constant period pulse output having a predetermined duty ratio is used. and turn on/off the power input to FET・Q.
I'm having them take off.

Note that the same effect can be obtained by using various semiconductor switching elements such as general transistors and thyristors in place of the FET/Q, and an astable multivibrator etc. is suitable as the oscillator OSC, but it is also possible to use various semiconductor switching elements such as general transistors and thyristors. oscillator
It may be replaced with OSC output.

FIG. 6 is a block diagram when one multiphase oscillator MPG is provided for multiple supply circuits LCF ₁ to LCF _o , and the switch S in each supply circuit LCF ₁ to _{LCF o} is a multiphase oscillator. It is designed to be driven by one specific phase in the output of the oscillator MPG.

Therefore, the switches S in each supply circuit LCF ₁ to LCF _o are not turned on at the same time, and the power supply B
Since power is supplied sequentially from 1 to 2, the load on power supply B is reduced and its voltage fluctuations are also reduced.

Note that the multiphase oscillator MPG can be easily realized by dividing the original oscillation frequency and using a decoder to output a multiphase output.

In some cases, the supply circuit LCF is required to exhibit a predetermined impedance to alternating currents such as talking current and signal current.
The AC impedance circuit AZC shown in the figure is inserted on the output side.

In other words, resistor R ₁ is connected to transistors Q ₁ and Q _2.
Forward bias is given by ~R ₆ and voltage regulator diode ZD ₁ + ZD ₂ , and transistors Q ₁ , Q ₂
The characteristics between the collector and emitter for direct current are:
Although it exhibits a relatively low resistance component and a voltage drop including a constant voltage component of several volts to several tens of volts, the capacitor C ₁
As a result, the bases of transistors Q ₁ and Q ₂ have the same potential in terms of alternating current, so they exhibit an impedance determined according to each constant with respect to alternating current applied between terminals t ₁ and t ₂ . , depending on the selection of the constants, a high impedance or a predetermined termination impedance is obtained.

In addition, this AC impedance circuit AZC is
“IEICE Technical Research Report” Vol.79, No.34,
An example of the basic configuration is shown in Table 1 on page 58 of ``A Consideration of Call Current Supply System'' described in SE79-20 (published by the Institute of Electronics and Communication Engineers of Japan), but any configuration can be used as long as it exhibits the same function. is applicable.

Figure 7 shows the AC impedance circuit.
As AZC, each element is inserted in each of both lines on the output side of the transfer circuit PTF, but depending on the conditions, as shown in Figure 8, an AC impedance circuit is inserted only in one line on the output side of the transfer circuit PTF. AZC may be inserted.

Further, as described above, since the collector-emitter of the transistors Q ₁ and Q ₂ exhibits a constant voltage drop characteristic and also exhibits an impedance component to alternating current, this can be used also as the voltage drop element DE.

In addition, it is also possible to replace the transformer T of the transfer circuit PTF with an inductance wire, and any configuration can be applied as long as it efficiently transfers a certain amount of power to the output side, and the present invention can be applied in various ways. can be freely modified.

As is clear from the above description, according to the present invention, the line current supply circuit that realizes a part of the BORSCHT function is mainly composed of electronic circuits, and the internal power consumption is extremely small. Not only is it easy to use electronic circuits and integrated circuits, but the structure is simple because no feedback control is required to drive the switch, and the line current supply circuit is smaller, lighter, and less expensive. It exhibits great effects in various exchangers.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an equivalent circuit of a line current supply system, Fig. 2 is a circuit diagram showing the principle of the present invention, and Fig. 3 is a diagram showing conventional line current supply characteristics and line current supply characteristics according to the present invention. 4 is a diagram showing the conventional power loss in the line current supply circuit and the power loss according to the present invention, and FIG. 5 and subsequent figures show embodiments of the present invention. FIG. 6 is a block diagram when a multiphase oscillator is used to drive the switch, and FIGS. 7 and 8 are circuit diagrams when an AC impedance circuit is inserted. LCF……Supply circuit (line current supply circuit), PTF
... Transfer circuit (power transfer circuit), DE ... Voltage drop element, ZD, ZD ₁ , ZD ₂ ... Constant voltage diode, r
...Resistor, B...Power supply, T...Transformer, T _P ...
...Primary winding, T _S ... Secondary winding, S ... Switch, D ... Diode, Q ... FET (field effect transistor), OSC ... Oscillator, MPG ... Multiphase oscillator, AZC ...AC impedance circuit.

Claims (1)

[Claims] 1. A power transfer circuit that transfers constant power to an output side, and a voltage drop element that includes at least a constant voltage component and is inserted in series to the output side of the power transfer circuit. line current supply circuit. 2. The line current supply circuit according to claim 1, wherein the voltage drop element includes a constant voltage component and a resistance component connected in series. 3. The power transfer circuit includes a transformer, a switch inserted in series into the primary winding of the transformer to turn on/off power input at a predetermined period, and a switch connected to the secondary winding of the transformer. Claim 1, characterized in that it consists of a diode inserted in series in a direction that becomes non-conductive when it is on.
The line current supply circuit described in . 4. The line current supply circuit according to claim 3, wherein the switch is driven by the output of an oscillator. 5. The line current supply circuit according to claim 3, wherein the switch is driven by one specific phase among the outputs of a multiphase oscillator. 6. The line current supply circuit according to claim 3, wherein the switch is a semiconductor switching element. 7 A power transfer circuit that transfers constant power to the output side, and an AC impedance circuit that also serves as a voltage drop element and includes at least a constant voltage component and is inserted in series to the output side of the power transfer circuit. line current supply circuit. 8. The line current supply circuit according to claim 7, wherein the AC impedance circuit includes a transistor that is forward biased through a constant voltage diode and a resistor connected in series. 9. The line current supply circuit according to claim 7, wherein the AC impedance circuit is inserted into each of both lines on the output side of the power transfer circuit. 10. The line current supply circuit according to claim 7, wherein the AC impedance circuit is inserted only in one line on the output side of the power transfer circuit. 11. The line current supply circuit according to claim 7, wherein the AC impedance circuit includes a resistance component and a constant voltage component.