JP3146631B2 - 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. Note that the DC resistance (RD + RH) is a specific resistance and does not change, but the input DC resistance RI changes with a duty ratio for driving the switching element Tr1 of the DC-DC converter CN.

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 Circuit, including a transformer having a primary winding and a secondary winding, and a switching element serially connected to the primary winding, and for using power of a DC component output from the DC separation circuit as a power supply of a line terminal device. DC-DC
Converter, a DC current supplied from the DC separation circuit to the DC-DC converter and a voltage applied to the input side of the DC separation circuit to detect a DC resistance value after the DC separation circuit, and The input DC resistance value viewed from the telephone line is calculated by adding the known DC resistance values from the rectifier circuit to immediately before the DC separation circuit, and the input DC resistance value is compared with the largest allowable resistance value allowed for the telephone line. DC-DC so as to converge to the maximum allowable resistance value.
A duty cycle control means for changing a duty cycle of a switching element of a converter is provided.

[0007]

In the circuit for utilizing telephone line power according to the present invention , D
The duty ratio of the switching element of the C-DC converter is controlled so that even if the line current changes, the DC resistance RS of the line terminal seen from the telephone line side is maximized within a range satisfying a predetermined standard. , The input DC resistance RI of the DC-DC converter is increased. In this case, the duty ratio 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 calculates the DC resistance value from the rectification circuit. A known DC resistance value 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. Next, this input DC resistance value is set to the largest allowable resistance value, for example, 3 which is allowed when connecting the line terminal equipment to the telephone line.
00 Ω. Thereafter, if the input DC resistance value of the line terminal equipment is far from the maximum allowable resistance value, such as being larger or smaller than this maximum allowable resistance value, the DC-D
The duty ratio of the switching element of the C converter is changed to converge to the maximum allowable resistance value. As a result, the input DC resistance RS of the line terminal 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 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. First Embodiment 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. In this telephone line power utilization circuit 1, the configuration of a bridge diode BD, a hook switch HS, an isolation transistor Q1, a low-pass filter LPF, and a DC-DC converter CN are the same as the conventional configuration except for a bias shunt resistance circuit of the isolation transistor Q1 described later. is there. DC-D
The C converter CN includes a bridge diode BD, a hook switch HS, and a DC isolation transistor Q from the telephone line side.
1 and a low-pass filter LPF to convert the DC voltage supplied to the line terminal equipment main body circuit TA for power supply. 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 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. Also, the base of the DC isolation transistor Q1 and the CPU 2 with the AD converter
A bias shunt resistor is connected between the two, and the bias current supplied by the base resistor RB can be changed by the operation of the CPU 2 with the AD converter. Further, the CPU 2 with the AD converter detects the input voltage after the line current supplied from the telephone line is rectified by the bridge diode BD, in other words, the collector-base voltage V1 which is the input side of the DC separation transistor Q1. Similarly, the voltage V2 between the emitter and the base, which is the output side of the DC isolation transistor Q1, is detected, and the voltage V3 across the resistor Rk is detected. The CPU 2 with the AD converter is a DC-D
The switching element Tr1 is connected to the control terminal of the switching element Tr1 of the C converter, and drives the switching element Tr1 with 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.

The CPU 2 with the AD converter has a DC-D
The primary side switching element Tr1 of the C converter CN is pulse-driven, but the DC resistance of the line terminal equipment viewed from the telephone line side is 300Ω or less, and the input DC resistance RI of the DC-DC converter CN is the maximum value. The duty ratio is controlled so that In addition, the bias is controlled so that the voltage drop in the DC isolation transistor Q1 does not exceed a necessary appropriate value. This allows DC
The loss in the isolation transistor Q1 is minimized, and D
The input DC resistance of the C-DC converter can be kept large,
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. If the line current I has reached the minimum current, the process proceeds to step ST6. Step ST
At 5, the DC-DC converter CN is turned off, and the process returns to step ST2.

In step ST6, the DC-DC converter CN is turned on. At this time, the duty ratio for pulse driving the primary-side switching element Tr1 of the DC-DC converter CN is the duty ratio stored in the memory. If it is not stored in the memory, the duty ratio is set to the maximum duty ratio in the controllable range (at this time, DC-
The input DC resistance RI of the DC converter CN is minimized).

Next, the CPU 2 with the AD converter detects the voltages V1 and V2 of FIG. 1 (step ST7), and
The voltage VCE (collector-emitter voltage) of the isolation transistor Q1 is calculated (step ST8). Next, the voltage V
CE is compared with an appropriate value (step ST9). This appropriate value is, for example, 1 of the amplitude of the signal component (2 V in the case of a modem).
/ 2. If voltage VCE> proper value, step S
Proceed to T10. If voltage VCE <proper value, step ST
Proceed to 11. If voltage VCE = proper value, step ST1
Proceed to 2. 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. In step ST11, 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 ST15. If RS <300Ω, the process proceeds to step ST16.
If RS = 300Ω, the process returns to step ST2. In step ST15, the duty ratio of the drive output from the drive output port that drives the switching element Tr1 in pulses is made larger than it is now. As a result, the DC resistance RS changes in a direction to decrease. Thereafter, the duty ratio is stored in the memory, and the process returns to step ST2. In step ST16, the duty ratio of the drive output from the drive output port is reduced. As a result, the DC resistance RS changes in a direction to increase. Thereafter, the duty ratio is stored in the memory, and the process returns to step ST2. As a result, the DC resistance RS converges to 300Ω in steps ST12 to ST16.

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

[0016]

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. Comparison In particular, the de <br/> Yuti ratio control means calculates a circuit resistance value by detecting the line current and the receiving voltage, the allowable resistance value within the range defined as standards the circuit resistance to the telephone line Then, since the duty ratio of the switching element of the DC-DC converter is controlled so that the circuit resistance value approaches the allowable resistance value, the line terminal equipment viewed from the telephone line side including the circuit resistance value of the telephone line power utilization circuit. The DC resistance can be maintained within a range that satisfies a predetermined standard required for telephone lines, and the input DC resistance of the DC-DC converter is maintained at a large value by changing the duty ratio of the switching element. and Ru it is possible to achieve a good receiving efficiency.

[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]

 1 telephone line power utilization circuit 2 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. A DC-DC converter that includes a transformer having a winding and a switching element connected in series to a primary winding and uses the power of the DC component output from the DC separation circuit as a power supply for line terminal equipment; A DC current supplied from the separation circuit to the DC-DC converter and a voltage applied to the input side of the DC separation circuit are detected to calculate a DC resistance value after the DC separation circuit. The input DC resistance value as viewed from the telephone line is calculated by adding the known DC resistance values immediately before the separation circuit, and the input DC resistance value is the largest allowable resistance value allowed for the telephone line. And a duty ratio control means for changing a duty ratio of a switching element of the DC-DC converter so as to converge to the maximum allowable resistance value as compared with.