JPH05344244A - Telephone line power utilization circuit - Google Patents

Abstract

PURPOSE:To improve receiving efficiency by controlling input DC resistance by switching the tap of the first order side coil of the transformer of a DC-DC converter. CONSTITUTION:In a telephone line power utilization circuit 101 utilizing DC power to be supplied from the side of a telephone line as the power source of a line terminal equipment main body circuit TA by a DC-DC converter CN, a CPU 22 with AD converter switches the tap of the first order side coil of the transformer of the DC-DC converter CN so that the DC resistance RS of the line terminal equipment viewed from the side of the telephone line may be within the range satisfying a prescribed specification and the input DC resistance of the DC-DC converter CN may be a maximum. Thus, DC power to be supplied from the side of the telephone line can be utilized to the maximum as the power source of the line terminal equipment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a telephone line power utilization circuit, and more particularly, to telephone line power which uses direct current power supplied from a telephone line as a power source for telephone line, modem, facsimile and other line terminal equipment. Regarding the circuit used.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional telephone line power utilization circuit 5.
It is a whole block diagram of 01. This telephone line power utilization circuit 5
In 01, the DC-DC converter CN includes the bridge diode BD, the hook switch HS, and the DC from the telephone line side.
The DC voltage supplied through the separation transistor Q1 and the low-pass filter LPF is supplied to the line terminal equipment main circuit TA.
Convert for power supply. Vcc is a battery or other external power source that serves as a power source for the line terminal equipment body circuit TA when the output from the DC-DC converter CN is insufficient. After the hook switch HS, the signal component is taken into a signal processing circuit (not shown) of the line terminal equipment body circuit TA via the DC cut capacitor C1 and processed.
The drive output circuit DO pulse-drives the switching element Tr1 of the DC-DC converter CN with a predetermined duty ratio.

FIG. 4 is a schematic diagram of a DC circuit composed of switching equipment, telephone lines and line terminal equipment. The DC resistance RS of the line terminal equipment seen from the telephone line side is the DC resistance RD of the bridge diode BD, the DC resistance RH of the hook switch, and the input DC resistance RI of the DC-DC converter.
, And RS = RD + RH + RI (1) According to the JATE standard, for example, the DC resistance RS is 50Ω when the line current I is 20 mA to 120 mA.
It is specified as ~ 300Ω (except for exceptions).

When the DC output voltage of the exchange equipment is E, the DC resistance of the exchange equipment is R1 and the line resistance is R2, the line current I is I = E / (R1 + R2 + RS) (2) R1 + R2 varies depending on the line length, but is usually larger than RS.

[0005]

When the input DC resistance RI of the DC-DC converter is large, the DC-DC converter CN can receive DC power from the telephone line side with high efficiency. However, the conventional telephone line power utilization circuit 5
In 01, since the DC resistance RS of the line terminal equipment viewed from the telephone line side is set to 50Ω to 300Ω, the input DC resistance RI of the DC-DC converter CN is set to be low as a whole, so that the power receiving efficiency is low. was there. Therefore, an object of the present invention is to provide a telephone line power utilization circuit in which the tap of the primary winding of a DC-DC converter is switched to control the input DC resistance and the power reception efficiency is improved.

[0006]

SUMMARY OF THE INVENTION In the telephone line power utilization circuit of the present invention, DC power supplied from the telephone line side is DC.
-In a telephone line power utilization circuit used as a power source for the line terminal equipment by the DC converter, so that the DC resistance of the line terminal equipment seen from the telephone line side satisfies a predetermined standard, and the received power of the DC-DC converter In order to increase the power consumption, a transformer tap switching means for switching the tap of the primary winding of the transformer of the DC-DC converter is provided.

[0007]

In the telephone line power utilization circuit of the present invention, the DC-
Range in which the DC resistance of the line terminal equipment seen from the telephone line side satisfies the specified standard even if the input DC resistance is controlled by switching the tap of the primary winding of the transformer of the DC converter and the line current changes. Inside, the input DC resistance RI of the DC-DC converter is increased. Therefore, it becomes possible to efficiently receive the DC power supplied from the telephone line.

[0008]

Embodiments of the present invention will now be described in more detail with reference to the drawings. However, this does not limit the present invention. FIG. 1 is an overall configuration diagram of a telephone line power utilization circuit 101 according to an embodiment of the present invention. In the telephone line power utilization circuit 1, the DC-DC converter C
N'converts a DC voltage supplied from the telephone line side through the bridge diode BD, the hook switch HS, the DC separation transistor Q1 and the low pass filter LPF to the power source of the line terminal equipment body circuit TA. Vcc is D
It is a battery or other external power source that becomes the power source of the line terminal equipment body circuit TA when the output from the C-DC converter CN is insufficient.

After the hook switch HS, the signal component is taken into a signal processing circuit (not shown) of the line terminal equipment body circuit TA through the DC cut capacitor C1 and processed.

A plurality of taps are provided on the primary side of the converter transformer of the DC-DC converter CN ', and switching elements Tr1 to Trn are connected to each tap.
The CPU 22 with an AD converter has a switching element T
Alternately selecting and operating r1 to Trn, switching the number of windings on the primary side of the converter transformer of the DC-DC converter CN ', and setting the DC resistance of the line terminal equipment as seen from the telephone line side to 300Ω or less. In such a range, the input DC resistance RI of the DC-DC converter CN is controlled to be the maximum value. Further, the bias is controlled so that the voltage drop in the DC separation transistor Q1 does not exceed a necessary proper value. As a result, it becomes possible to efficiently receive the DC power supplied from the telephone line.

FIG. 2 is a flow chart showing the operation of the CPU 22 with an AD converter. When the hook switch HS enters the off-hook state (step ST1), the voltage V of FIG.
3 is detected (step ST2), and the line current I is calculated by I = V3 / Rk (step ST3). However, Rk is the resistance value of the current detection resistor. Next, it is determined whether or not the line current I has reached the minimum current (about 15 mA) of the telephone line (step ST5). If the line current I has not reached the minimum current, the process proceeds to step ST5, and if it has reached the minimum current, the process proceeds to step ST6. In step ST5,
Turning off the DC-DC converter CN, step S
Return to T2.

At step SU6, the DC-DC converter CN is turned on. At this time, the switching element to be operated selectively is the switching element stored in the memory. If it is not stored in memory,
The switching element has the smallest number of turns (at this time, the input DC resistance RI of the DC-DC converter CN becomes the minimum value).

Next, the voltages V1 and V2 in FIG. 1 are detected (step ST7), and the voltage VCE of the DC separation transistor Q1 is detected.
(Collector-emitter voltage) is calculated (step S
T8). Next, the voltage VCE is compared with an appropriate value (step ST9). This appropriate value is, for example, about 1/2 of the amplitude of the signal component (2V in the case of a modem). If the voltage VCE> appropriate value, the process proceeds to step ST10. If the voltage VCE <appropriate value, the process proceeds to step ST11. If the voltage VCE = appropriate value, the process proceeds to step ST12. In step ST10, the control port CP is controlled to increase the value of the bias shunt resistance and increase the bias current. As a result, the voltage VCE changes in a decreasing direction. Step S
At T11, the control port CP is controlled to reduce the value of the bias shunt resistance and reduce the bias current. As a result, the voltage VCE changes in the increasing direction. After all, the voltage VCE converges to an appropriate value in steps ST7 to ST11.

At step ST12, the voltages V1 and V3 are detected. Next, the DC resistance RS of the telephone line power utilization circuit 1 viewed from the telephone line side is calculated by I = V3 / Rk RS = (V1 / I) + (RD + RH) (step ST13). Next, the DC resistance RS is compared with 300Ω (preferably a value slightly smaller than 300Ω) (step ST14). RS> 300Ω
If so, the process proceeds to step ST15. If RS <300Ω, the process proceeds to step ST16. If RS = 300Ω,
The process returns to step ST2.

In step SU15, a switching element whose number of turns is smaller than that of the present is selected. As a result, the DC resistance RS changes in the direction of decreasing. After that, the switching element is stored in the memory, and the process returns to step ST2. In step SU16, a switching element having a larger number of turns than the current one is selected. As a result, the DC resistance RS changes in the increasing direction. After that, the switching element is stored in the memory, and the process returns to step ST2. After all, step S
From T12 to step SU16, the DC resistance RS is 3
Converges to 00Ω.

As described above, the DC power supplied from the telephone line can be efficiently received.

[0017]

According to the telephone line power utilization circuit of the present invention,
The DC power supplied from the telephone line side can be used to the maximum as the power source for the line terminal equipment.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a telephone line power utilization circuit according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing the operation of the telephone line power utilization circuit of FIG.

FIG. 3 is an overall configuration diagram of a conventional telephone line power utilization circuit.

FIG. 4 is a schematic diagram of a DC circuit.

[Explanation of symbols]

 101 telephone line power utilization circuit 22 CPU with AD converter CN DC-DC converter TA line terminal device main circuit

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[Procedure amendment]

[Submission date] June 8, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

Claims (1)

[Claims] 1. The DC power supplied from the telephone line side is D
In a telephone line power utilization circuit used as a power source for a line terminal device by a C-DC converter, the DC resistance of the line terminal device viewed from the telephone line side satisfies a predetermined standard, and the DC-DC converter receives power. A telephone line power utilization circuit comprising transformer tap switching means for switching taps of a primary winding of a transformer of a DC-DC converter so as to increase power.