JP3146632B2 - Telephone line power utilization circuit - Google Patents

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 a telephone line power supply that uses DC power supplied from a telephone line as a power source for line terminal equipment such as telephones, modems and facsimiles. Regarding the utilization circuit.

[0002]

2. Description of the Related Art FIG. 3 is a diagram showing the overall configuration of a telephone line power utilization circuit 501 of a conventional line terminal device. In this telephone line power utilization circuit 501, a DC-DC converter CN
Converts the DC voltage supplied from the telephone line through the bridge diode BD, the hook switch HS, the DC separation transistor Q1, and the low-pass filter LPF to the power for the line terminal equipment main circuit TA. The bridge diode BD rectifies the line current I supplied from the telephone line. The hook switch HS is a switch that closes when the line terminal device is operated. The DC separation transistor Q1 separates the DC component while securing the signal component of the line current I, and limits the power extracted from the telephone line. The low-pass filter LPF removes noise from the output of the DC isolation transistor Q1, and absorbs fluctuations in the line current I flowing through the telephone line due to the switching operation of the DC-DC converter CN. Note that Vcc
Is a battery or other external power supply that serves as a power supply for the line terminal equipment main circuit TA when the output from the DC-DC converter CN is insufficient. After the hook switch HS, the signal component is taken into the signal processing circuit (not shown) of the line terminal equipment main body circuit TA via the DC cut capacitor C1 and processed. The drive output circuit DO has a DC-
The switching element Tr1 of the DC converter CN is pulse-driven at a predetermined duty ratio.

FIG. 4 is a schematic diagram of a DC circuit composed of switching equipment, a telephone line, and line terminal equipment. The DC resistance RS of the line terminal equipment viewed 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.
RS = RD + RH + RI (1) According to the JATE standard, for example, according to the JATE standard, the DC resistance RS is 50Ω when the line current I is 20 mA to 120 mA.
３００300 Ω (excluding exceptions). That is, the DC resistance RS may be set to an allowable resistance value within a range allowed for the telephone line. The DC resistance (RD + RH) is a specific resistance and does not change.

If the DC output voltage of the switching equipment is E, the DC resistance of the switching 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 with high efficiency. However, the conventional telephone line power utilization circuit 5
In No. 01, the input DC resistance RI of the DC-DC converter CN was set to be relatively low in order to set the DC resistance RS of the line terminal equipment as viewed from the telephone line side to 50Ω to 300Ω. was there. SUMMARY OF THE INVENTION An object of the present invention is to provide a telephone line power utilization circuit in which the DC resistance RS seen from the telephone line side is maintained within a range permitted for the telephone line and the power receiving efficiency of the DC-DC converter is improved. It is in.

[0006]

SUMMARY OF THE INVENTION This invention comprises a rectifier circuit for rectifying the line current comprising an AC component and a DC component supplied from the telephone line, a direct current separation for separating the DC component of the output of the rectifier circuit A DC component output from the DC separation circuit including a circuit, a transformer having a primary winding and a secondary winding, and switching elements connected to each of a plurality of taps drawn from the middle of the primary winding. A DC-DC converter for utilizing the power of the DC power supply as a power source for line terminal equipment, and detecting a DC current supplied from the DC separation circuit to the DC-DC converter and a voltage applied to an input side of the DC separation circuit. Then, the DC resistance value after the DC separation circuit is calculated, and the known DC resistance value from the rectification circuit to immediately before the DC separation circuit is added thereto, and the input DC resistance viewed from the telephone line is added. And compare the input DC resistance with the largest allowable resistance allowed for the telephone line and tap the primary winding tap of the transformer of the DC-DC converter to converge on the maximum allowable resistance. And a transformer tap switching control means for switching.

[0007]

In the circuit for utilizing telephone line power according to the present invention , D
The input DC resistance RI is controlled by switching the tap of the primary winding of the transformer of the C-DC converter, and even if the line current changes, the DC resistance RS of the line terminal equipment viewed from the telephone line side.
Is maximized within a range satisfying a predetermined standard.
The input DC resistance RI of the C-DC converter is increased.
In this case, the transformer tap switching control means detects the DC current supplied to the DC-DC converter and the voltage applied to the input side of the DC separation circuit, calculates the DC resistance value after the DC separation circuit, and rectifies it. A known DC resistance value from the circuit to immediately before the DC separation circuit is added to calculate an input DC resistance value RS as viewed from the telephone line side of the line terminal equipment including the telephone line power utilization circuit. Then, the input DC resistance value is compared with the largest allowable resistance value, for example, 300Ω, which is allowed when the line terminal device is connected to the telephone line. Thereafter, if there is a difference from the maximum allowable resistance value, such as the input DC resistance value of the line terminal equipment being larger or smaller than the maximum allowable resistance value, tap the primary winding of the transformer of the DC-DC converter. By switching, the input DC resistance RI of the DC-DC converter is changed to converge to the maximum allowable resistance value. As a result, the input DC resistance RS of the line terminal equipment seen from the telephone line side satisfies a predetermined standard set for the telephone line, and the input DC resistance RI of the DC-DC converter becomes the largest, and the supply from the telephone line becomes large. The received DC power can be efficiently received.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in more detail with reference to the drawings. It should be noted that the present invention is not limited by this. FIG. 1 is an overall configuration diagram of a telephone line power utilization circuit 1 of a line terminal device according to a first embodiment of the present invention.
Located between A and the telephone line. In this telephone line power utilization circuit 1, a bridge diode BD, a hook switch H
The configuration of S, the isolation transistor Q1, the low-pass filter LPF, and the DC-DC converter CN 'is the same as the conventional configuration except for a bias shunt resistance of the isolation transistor Q1 described later. The DC-DC converter CN 'is connected to the bridge diode BD, the hook switch HS and the DC from the telephone line side.
The DC voltage supplied via the isolation transistor Q1 and the low-pass filter LPF is converted to the line terminal equipment main body circuit TA.
Convert for power supply. VCC is a DC-DC converter C
This is a battery or other external power supply that becomes a power supply for the line terminal equipment main circuit TA when the output from N ′ is insufficient.

After the hook switch HS, the signal component is taken into the signal processing circuit (not shown) of the line terminal equipment main circuit TA via the DC cut capacitor C1 and processed. A parallel circuit of a current detection resistor Rk and a capacitor is connected between the DC-DC converter CN ′ and the low-pass filter LPF to detect the line current I. In addition, the base of DC isolation transistor Q1 and CPU with AD converter
2, a bias shunt resistor is connected, and the bias current supplied by the base resistor RB can be changed by the operation of the CPU 2 with an AD converter. In addition, the CPU 2 with the AD converter is configured to control the input voltage after the line current supplied from the telephone line is rectified by the bridge diode BD,
In other words, the voltage V1 between the collector and the base, which is the input side of the DC separation transistor Q1, is detected. Similarly, the voltage V2 between the emitter and the base, which is the output side of the DC separation transistor Q1, is detected. V3 is detected. The CPU 2 with the AD converter is a DC-
The switching terminals Tr1 to Trn of the DC converter are connected to control terminals of the switching devices Tr1 to Trn, respectively, and pulse-drive the selected switching devices at a predetermined duty ratio. The input DC resistance RI of the DC-DC converter CN ′ is provided by a series circuit of a primary winding of a converter transformer and a switching element Tr1.

[0010] 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 the respective taps.
The CPU 22 with the AD converter includes a switching element T
By selectively selecting and operating r1 to Trn, the number of windings on the primary side of the converter transformer of the DC-DC converter CN 'is switched so that the DC resistance of the line terminal equipment as viewed from the telephone line side becomes 300Ω or less. Control is performed so that the input DC resistance RI of the DC-DC converter CN 'becomes a maximum value within a certain range. In addition, the bias is controlled so that the voltage drop in the DC isolation transistor Q1 does not exceed a necessary appropriate value. Thereby, the input DC resistance of the DC-DC converter can be maintained large, the loss in the DC isolation transistor Q1 can be minimized, and the DC power supplied from the telephone line can be efficiently received. .

FIG. 2 is a flowchart showing the operation of the CPU 2 with an AD converter. When the hook switch HS enters the off-hook state (step ST1), the voltage V3 in FIG.
Is detected (step ST2), and the line current I is calculated by I = V3 / Rk (step ST3). Here, 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 of the telephone line (for example, about 15 mA) (step ST4). If the line current I has not reached the minimum current, the process proceeds to step ST5, and if the line current I has reached the minimum current, the process proceeds to step SU6. Step ST
At 5, the DC-DC converter CN ′ is turned off,
It returns to step ST2.

In step SU6, the DC-DC converter CN 'is turned on. At this time, the switching element to be operated alternatively is a switching element stored in the memory. When not stored in the memory, the primary winding of the converter transformer is a switching element connected to the tap having 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 of FIG. 1 are detected (step ST7), and the voltage VCE of the DC isolation 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 程度 of the amplitude of the signal component (2 V in the case of a modem). If voltage VCE> proper value, the process proceeds to step ST10. If the voltage VCE <the appropriate value, the process proceeds to step ST11. If the voltage VCE is an 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 direction to decrease. Step S
At T11, the control port CP is controlled to reduce the value of the bias shunt resistance, thereby reducing the bias current. As a result, the voltage VCE changes in a direction to increase. As a result, the voltage VCE converges to an appropriate value in steps ST7 to ST11.

In step ST12, 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 / RkRS = (V1 / I) + (RD + RH) (step ST13). That is, since the DC resistance (RD + RH) is a fixed resistance, if it is processed as a constant, the DC resistance RS can be easily obtained by calculating (V1 / I). Next, the DC resistance RS is compared with the largest allowable resistance value 300 Ω (preferably slightly smaller than 300 Ω) of the telephone line (step ST).
14). If RS> 300Ω, the process proceeds to step SU15. If RS <300Ω, the process proceeds to step SU16.
If RS = 300Ω, the process returns to step ST2.

In step SU15, a switching element connected to a tap such that the number of turns of the primary winding of the converter transformer is smaller than the current number is selected. As a result, the DC resistance RS changes in a direction to decrease. Thereafter, the switching element is stored in the memory, and the process returns to step ST2. In step SU16, the switching element connected to the tap such that the number of turns of the primary winding of the converter transformer becomes larger than the current number is selected. As a result, the DC resistance RS changes in a direction to increase. Thereafter, the switching element is stored in the memory, and the process returns to step ST2. After all, step S
From step T12 to step SU16, the DC resistance RS becomes 3
It converges to 00Ω.

By repeating the above steps, DC power supplied from the telephone line can be efficiently received.

[0017]

According to the telephone line power utilization circuit of the present invention,
DC power supplied from the telephone line side can be used to the utmost as a power source for line terminal equipment. In particular, varying <br/> divider tap switching control means calculates a circuit resistance value by detecting the line current and the receiving voltage, a permissible resistance value within the range defined as standards the circuit resistance to the telephone line In comparison, since the input DC resistance value is controlled by selecting the tap of the primary winding of the DC-DC converter so that the circuit resistance value approaches the allowable resistance value, the circuit resistance value of the telephone line power utilization circuit is included. The DC resistance of the line terminal equipment viewed from the telephone line side can be maintained within a range that satisfies a predetermined standard required for the telephone line, and the input DC resistance of the DC-DC converter is controlled by the primary winding. Ru can be achieved with good power receiving efficiency of maintaining a large value by changing the number of turns.

[Brief description of the 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 Equipment Main Circuit

Continuation of the front page (58) Fields investigated (Int. Cl. ⁷ , DB name) H04M 19/00-19/08 H04M 1/00 H04M 11/00-11/10 H04Q 3/42

Claims (1)

(57) [Claims] A rectifier circuit for rectifying a line current including an AC component and a DC component supplied from a telephone line, a DC separation circuit for separating a DC component of an output of the rectifier circuit, a primary winding and a secondary winding. The power of the DC component output from the DC separation circuit including the transformer having the secondary winding and the switching element connected to each of the plurality of taps drawn from the middle of the primary winding is used as the power supply of the line terminal equipment. A DC-DC converter for use, and a DC current supplied from the DC separation circuit to the DC-DC converter and a voltage applied to an input side of the DC separation circuit to detect DC current after the DC separation circuit. A resistance value is calculated, and a known DC resistance value from the rectifier circuit to immediately before the DC separation circuit is added thereto to calculate an input DC resistance value viewed from the telephone line, and the input DC resistance value is calculated. Transformer tap switching control means for switching the tap of the primary winding of the transformer of the DC-DC converter so as to converge to the maximum allowable resistance value as compared with the maximum allowable resistance value allowed for the telephone line. A telephone line power utilization circuit, comprising: