JPH05292228A - Dc power receiving circuit - Google Patents

Abstract

PURPOSE:To provide a DC power receiving circuit which can be used even if the line resistance is increased up to a level where a loop current is identical with a working current of a loop detecting relay. CONSTITUTION:A constant voltage element 1 is provided between both terminals through which the DC current flows from a DC constant voltage power supply 21 of a switchboard via a loop detecting relay 22, a line 30 and a hook switch 50. Thus, the element 1 functions to turn a loop current into a constant current even if the line resistance varies between a base and one of both terminals. Meanwhile, a resistor R4 is connected between a collector and an emitter. In regard of a transistor Tr of such a constitution and a DC power receiving circuit 10 containing a series circuit of a resistor R3 and a voice signal transmission/reception part 40 connected between both terminals of the series circuit, a constant voltage element 2 which secures the constant voltage at a level slightly higher than the peak value of the voice signal received from the part 40 is set between the R4 and the base of the Tr.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a signal conversion circuit or the like for converting a voice signal of a PCM primary group terminal device into a digital signal, and makes a loop current constant even when the line resistance changes during on-hook. Regarding improvement of power receiving circuit.

The loop current supplied from the DC power supply circuit of the exchange becomes large when the line resistance between the PCM primary group terminal devices is small, and the power consumption becomes large. Therefore, in order to keep the line resistance at least a constant current. , A DC power receiving circuit is used for the signal conversion circuit of the PCM primary group terminal device,
It is desired that this DC power receiving circuit can be used even if the line resistance becomes large until the loop current becomes a moving current of the loop detection relay.

[0003]

2. Description of the Related Art FIG. 4 is a circuit diagram centering on a conventional DC power receiving circuit, and FIG. 5 is a loop current characteristic diagram of FIG.

In FIG. 4, C1, C2, and C3 are capacitors for cutting direct current, C4 is a capacitor for bypassing audio signals, and R is a capacitor.
1 is the resistance of the loop detection relay 22-1, L1 is the inductance of the loop detection relay 22-1, R2 is the resistance of the loop detection relay 22-2, L2 is the inductance of the loop detection relay 22-2, Ra, Rb is the resistance of the line 30, R3 and R4 are resistors, Tr is a transistor, and ZD1.
Represents a Zener diode, and T represents a hybrid transformer.

In FIG. 4, when the hook switch 50 is turned on, the loop current from the -48V battery 21 of the DC power supply circuit 20 of the exchange is switched to the loop detection relays 22-1, 22-1.
22-2, the line 30, and the DC power receiving circuit 10 ′.

The voice signal is transmitted and received between the voice signal transmitting / receiving unit 40 of the signal conversion circuit of the PCM primary group terminal device and the trunk circuit of the exchange, and the peak of the output voltage of the voice signal of the voice signal transmitting / receiving unit 40 is about 3V. Therefore, the sensing current of the loop detection relays 22-1, 22-2 is about 10 mA.

In this case, the loop current flowing through the DC power receiving circuit 10 'is a constant current of, for example, 15 mA, which is a moving current of the loop detection relays 22-1, 22-2 which is larger than 10 mA, and the transistor Tr has a peak of an audio signal. In order to prevent saturation at the voltage and decrease in the impedance between the collector and the emitter, the resistance R3 = 200Ω,
Voltage Vbe between the base and emitter of the transistor Tr =
When 0.7V is set, the Zener diode ZD1 having a Zener voltage of 3.7V is used.

In this way, the line resistances Ra and Rb are
Increase, the voltage across resistor R3 is 3V, zener diode
Loop voltage is applied until the voltage across the terminal ZD1 reaches 3.7V.
Flow I _LIs a constant current.

The loop current I _{L in} this case is expressed by the following equation (1). I _L = [Vzd1-Vbe] / R3 (1) where Vzd1 = Zener voltage of zener diode ZD1, Vbe = voltage between base and emitter of transistor Tr, but line resistances Ra and Rb further increase However, when the voltage across the resistor R3 becomes 3 V or less and the voltage across the Zener diode ZD1 becomes 3.7 V or less, the base voltage is not constant and the transistor Tr is saturated by the beak voltage of the audio signal, so that Since the impedance between the collector and the emitter becomes extremely small, the loop current becomes smaller as the line resistances Ra and Rb increase, and the loop current I _{L in} this case is expressed by the following equation (2).

I _L = [Vbb−Vce (sat)] / (R1 + R2 + Ra + Rb + R3) ... (2) where Vbb is the voltage of the −48V battery 21, Vce (sa
t) is a voltage between the collector and the emitter when the transistor Tr is saturated by an audio signal and is about 0.

(1) when the line resistances Ra and Rb are increased
As shown in FIG. 5, the loop current characteristic expressed by the equation (2) is constant until the voltage across the resistor R3 becomes 3V,
When the voltage becomes 3 V or less, the transistor Tr is saturated by the peak voltage of the audio signal, and the impedance between the collector and the emitter of the transistor Tr becomes almost 0, so that it decreases.

At the point that the voltage across the resistor R3 in FIG. 5 becomes 3 V or less, the loop current is larger than the sensing currents of the loop detection relays 22-1, 22-2, but the transistor T
When the impedance between the collector and the emitter of r becomes almost 0, the input impedance of the DC power receiving circuit 10 'becomes the resistance value of the resistor R3 of 200Ω, which is smaller than the line impedance of 600Ω and the insertion loss increases. If the line resistance increases, the DC power receiving circuit 10 'cannot be used.

[0013]

As described above, in the conventional DC power receiving circuit, the line resistance increases and the voltage across the resistor R3 becomes 3 V or less which is the peak voltage of the audio signal. Are loop detection relays 22-1, 2
Although the transistor Tr is saturated and the insertion loss is large regardless of the touching current of 2-2, it cannot be used until the loop current becomes the touching current of the loop detection relays 22-1, 22-2. is there.

It is an object of the present invention to provide a DC power receiving circuit which can be used even when the line resistance is increased until the loop current becomes a moving current of the loop detection relay.

[0015]

FIG. 1 is a block diagram showing the principle of the present invention. As shown in FIG. 1, a DC current sent from the DC constant voltage power source 21 of the exchange through the loop detection relay 22, the line 30, and the hook switch 50 is flown between the one end and the other end, the base and the other end. A transistor Tr and a first resistor R3 in which a first constant voltage element 1 for connecting a loop current to a constant current is connected and a second resistor R4 is connected between a collector and an emitter even if the line resistance changes Of the audio signal transmitter / receiver 40 between the one end and the other end.
In the DC power receiving circuit 10 to which is connected, a second voltage between the second resistor R4 and the base of the transistor Tr is set to a constant voltage with a voltage slightly larger than the peak value of the audio signal from the audio signal transmitting / receiving unit 40. The constant voltage element 2 is inserted.

[0016]

According to the present invention, until the line resistance is increased and the voltage across the resistor R3 reaches the peak value of the audio signal, the constant current is the same as in the conventional case, and the audio is output between the collector and the base of the transistor Tr. Since the second constant voltage element 2 that is a constant voltage with a voltage slightly higher than the peak value of the audio signal from the signal transmitting / receiving unit 40 is inserted, even if the line resistance is further increased, the input voltage of the DC power receiving circuit 10 is increased. Since the voltage between the collector and the base of the transistor Tr is kept at the constant voltage of the second constant voltage element 2 until the peak value of the audio signal is reached, the impedance does not decrease and the DC power receiving circuit 10 has a loop current. It can be used until the exciting current of the loop detection relay is reached.

[0017]

FIG. 2 is a circuit diagram centering on a DC power receiving circuit according to an embodiment of the present invention, and FIG. 3 is a loop current characteristic diagram in the case of FIG.

2 is different from the conventional example of FIG. 4 in that a Zener diode ZD2 having a Zener voltage Vzd2 is inserted between the resistor R4 of the DC power receiving circuit 10 and the base of the transistor Tr. Will be described below.

The line resistances Ra and Rb are increased to increase the resistance of the resistor R3.
Loop current I until the voltage of both ends becomes 3V_LIs shown in Figure 3
As is the case with the conventional example, the constant current is 15 mA. Change
If the line resistances Ra and Rb are increased to
Between the collector and the base of the sound signal transmitting and receiving unit 40
3V, a voltage slightly higher than the peak value of the voice signal of
Insert a Zener diode ZD2 with a gate voltage Vzd2
Since it is turned on, even if the line resistance is further increased, the DC
Until the input voltage of the electric circuit 10 reaches the peak value of the audio signal
The voltage between the collector and base of the transistor Tr is 3V
Since the zener voltage is kept at Vzd2, the impedance
Is not reduced, and the loop current I _LIs given by the following equation (3)
Become so.

I _L = [Vbb−Vce] / (R1 + R2 + Ra + Rb + R3) = [Vbb−Vzd2] / (R1 + R2 + Ra + Rb + R3) (3) The loop current characteristic in this case is as shown by the solid line in FIG. 3, and the loop current is Since the impedance between the collector and the emitter of the transistor Tr does not become small even if the line resistances Ra and Rb are increased until the loop detection relay has the exciting current, the DC power receiving circuit 10 changes the loop current into the exciting current of the loop detecting relay. Can be used until

[0021]

As described in detail above, according to the present invention, the DC power receiving circuit can be used until the line resistance increases and the loop current becomes the moving current of the loop detecting relay.

[Brief description of drawings]

FIG. 1 is a block diagram of the principle of the present invention,

FIG. 2 is a circuit diagram centering on a DC power receiving circuit according to an embodiment of the present invention,

3 is a loop current characteristic diagram in the case of FIG. 2,

FIG. 4 is a circuit diagram centering on a conventional DC power receiving circuit,

FIG. 5 is a loop current characteristic diagram in the case of FIG.

[Explanation of symbols]

1, 2 are constant voltage elements, 10 and 10 'are DC power receiving circuits, 2
0 is a DC power supply circuit, 21 is a DC constant voltage power supply, -48V battery, 22, 22-1, 22-2 are loop detection relays,
30 is a line, 40 is a voice signal transmitting / receiving unit, 50 is a hook switch, C1 to C4 are capacitors, R1 to R4, Ra,
Rb is a resistance, L1 and L2 are inductances, Tr is a transistor, ZD1 and ZD2 are zener diodes, and T is a hybrid transformer.

Claims (1)

[Claims] 1. A DC constant voltage power source (21) for an exchange.
Loop detection relay (22), line (30), hook switch
The DC current sent through the switch (50) is flown, and loop current is generated between one end and the other end even if the line resistance changes between the base and the other end.
Connect the first constant voltage element (1) for constant current
A second resistor (R4) was connected between the reflector and emitter
Series connection of transistor (Tr) and first resistor (R3)
Insert the channel and connect the audio signal transceiver (40) between the one end and the other end.
In the continuous DC power receiving circuit (10), the base of the second resistor (R4) and the transistor (Tr) is
Between the voice signal from the voice signal transmitting / receiving unit (40)
Second constant voltage with a voltage slightly higher than the peak value
DC power receiving circuit characterized by inserting a piezoelectric element (2)
Road.