JPS61121563A - Power supply circuit for telephone set call circuit - Google Patents

Abstract

PURPOSE:To set freely a VL-LL characteristic by equipping a power supply bypass circuit composed of a transistor and a resistance on a current source. CONSTITUTION:When a voltage is impressed between input terminals P3 and P4 and a voltage of 0.7 V arises in the resistance 21, a PNP type transistor 33 enters an active area, and the VL-LL characteristic appears at the low current side as shown by polygoval line. If the resistance R21 is set larger than the resistance R32, the resistance R21 + resistance R22 can be set larger. Accordingly a low line voltage can cope with an increase in a line current as DC impedance standards are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a power supply circuit for an electronic telephone communication circuit.

The structure of a conventional example and its problems A simplified structure of a telephone set is shown in FIG. Pl and P
l is the input/output terminal of the telephone that is connected to the telephone line from the telephone office; DC voltage and reception signals are sent through lines 1 and 2, and calls are sent from the telephone through lines 1 and 2 to the telephone office. It is an external terminal on a telephone that sends signals. These terminals P1 and Pl are connected to the main part 'f of the telephone: the soot communication circuit 6 through the diode bridge 3 and the internal line 3.4vC. The functions of the communication circuit 6 are to draw in a predetermined DC current, convert the received signal into an audio signal through the speaker, convert the audio signal into an electrical signal using the microphone, and send the transmitted signal to the telephone office through Pl and Pl. It is to send out. Figure 2 shows the DC characteristics required for a telephone. According to the standard specifications, the telephone set has a DC current L = 2 ohmA to 100 mA,
DC impedance vL'/Eq.L = 60 to 220Ω. DC voltage in the above range.

Looking at the current characteristics, the upper and lower limits are shown by dashed lines 7 and 8 in FIG. As shown in FIG. 1, the telephone is comprised of a diode bridge 3 and a communication circuit θ, and the voltage drop across the diode bridge 3 is generally about 1.4V. The voltage and current ranges allowed for the communication circuit after subtracting the voltage drop of the diode bridge 3 are shown by the solid lines 9 and 1 in Figure 2.
This is the area surrounded by o. Solid lines 11& and 11b are examples of the DC power supply characteristics of the communication circuit falling in this region.

For example, in the solid line 11b, the construction = 2om person @M
L: 3 V, IL = 10071A @ vL
=:sv. Also, solid lines 112L and 11b
is the case where the communication circuit is integrated, and B"CEO=10"
This is the appropriate setting when the i process is adopted.

Next, the characteristic required for a telephone set is a characteristic impedance of 600Ω. In order to achieve this characteristic impedance, the characteristic impedance required for the communication circuit is 2.
It is desirable that the resistance is Ω or more. Next, a direct current voltage is applied to the input terminals p1 and p2 of the telephone, and an alternating current signal such as a voice transmission signal and a DTMF (fual tone multifrequency) signal is superimposed on the input terminals p1 and p2 of the telephone. Ru.

For this reason, the communication circuit needs to have a configuration that is free from distortion and can swing in alternating current. In general, when the line voltage vL is lowered in an electronic telephone communication circuit, the current on the line stops flowing at a certain voltage. The voltage at which this current IL stops flowing will be referred to as the saturation voltage ML (SaLt). In order for input terminal P1-p2 to swing by 3Vpp, VL(sa
t)" 1.5v is required〇Generally, the internal power supply that drives the communication circuit is 1.7v to 2v, and VL(j
i&t)≦1. In order to realize svl, circuit-related improvements are required. The main characteristics required for the power supply of the communication circuit described above are summarized as follows.

■DC characteristics I t, = 20mA (7) ,! : @
'IL-43VI L: 100mA throat 3.6v≦
vL≦2o, 6■Characteristic impedance is 2Ω or more■YL(S+Lt)≦1.5v
A circuit example is shown in FIG. 4.

In FIG. 3, P5 and P4 are input terminals and the voltage v
L is applied and current flows in. P5 is an output terminal of a constant voltage source for driving the communication circuit. Further, 12 is a constant current circuit, which is a circuit for keeping the DC impedance within the standard.

13 is an electronic switch, which is a circuit for lowering the saturation voltage. 14 is a backflow prevention circuit, 16 is a constant voltage circuit that creates a voltage for driving the communication circuit, and 16 is a comparison control circuit. Reference numeral 16 denotes a comparison control circuit that generates a signal to activate the electronic switch 13.

FIG. 4 shows a specific circuit example of the conventional device shown in FIG. 3, and the structure of each broken line frame in this figure corresponds to each circuit shown in FIG. In addition, in FIG. 4, 18 is a capacitor, 19.
20 is a PNP transistor, 21 and 22 are resistors, 24 is a PNP transistor, 26 is a resistor, 27 is a PNP transistor, 2 are capacitors, and 30 is a diode.

The DC characteristics of the conventional example will be explained with reference to FIG. For the sake of simplicity, the base-emitter voltage Y3E in the active region of each transistor is 0. TV, DC current amplification factor 11f, =a
Let it be O. Note that an explanation that takes into account exact '1VBv and hfe is also possible, but this does not affect the explanation of the basic operation.

Typically, current mirror coupled PNP transistors 19 and 20
The emitter area ratio is set to 1:H. Terminal P
The DC voltage vL applied between 5 and P4 is VL = 0.
7'/, a current begins to flow through the PNP transistor 19, and this current is mirrored to the PNP transistor 20, so that N times the current flows. In this way, the DC characteristics are determined, and the line current IL is expressed by the following equation. However, R
21+R22 are the respective resistance values of the resistors 21 and 22.

From the required DC characteristics, IL: 20? When there are z people, Vl = 3V. Substituting these, equation (1) becomes the following equation. Here, it is assumed that N=20 as a general value.

Rz1+ R22 now 2.4Ω (2)
Since the capacitor 18 is set to have a sufficiently low impedance with respect to alternating current, the characteristic impedance is 2.4Ω or less. Further, due to the Early effect of the transistor 20, etc., the characteristic impedance between the terminals P5 and P4 further decreases. In order to increase this impedance, it is necessary to set N to a large value, which results in an increase in the area of the element.

Further, vL when IL=100 mA cannot be set freely, resulting in a high voltage, so it is necessary to adopt a process with high breakdown voltage. The DC characteristics of this conventional circuit are shown by the solid line 11'B- in FIG.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a power supply circuit for a telephone communication circuit which uses a small number of elements, eliminates the above-mentioned drawbacks, and can be easily integrated.

Structure of the Invention To summarize, the present invention comprises a comparison control circuit, a backflow prevention circuit, and It is characterized in that it is connected in parallel with a constant voltage circuit, has a constant voltage output terminal at the constant voltage connection point with the reverse current prevention circuit, and is provided with a current bypass circuit consisting of a transistor and a resistor in the constant current source. This is a power supply circuit for a telephone communication circuit, and the provision of this current bypass circuit increases the degree of freedom in setting the vL-IL characteristics.

DESCRIPTION OF EMBODIMENTS FIG. 5 shows an embodiment of the present invention.
The circuit configuration diagram is shown in the figure.

In FIG. S, P5 and P4 are input terminals, to which a voltage vL is applied and a current IL flows into them.P5 is an output terminal of a constant voltage source for driving the communication circuit. 12 is a constant current circuit, which is a circuit for keeping the DC impedance within the standard. 13 is a circuit that is turned on by an electronic switch connected to the constant current source 12 to lower the saturation voltage. 16 is a comparison control circuit that generates a signal to drive the electronic switch 13. Reference numerals 14 and 15 denote a series connection of a backflow prevention circuit and a constant voltage circuit, which are connected in series to the constant current circuit 12 together with the electronic switch 13 . 31 is a current bypass circuit, and in FIG. 6, the emitters of PNP transistors 19 and 20 having a common base are connected to the input terminal P3, and the base-collector common connection point of the transistor 190 and the other input terminal P4 are connected. There is a resistance 21 between
．． 22 in series and the intermediate connection point between both resistors 21 and 22 are connected to the base, and the emitter and collector of a PNPI transistor 33 having a resistor 32 on the emitter side are connected, respectively. Further, the base of the PNP transistor 24 is connected to the intermediate connection point between the resistor 21 and the resistor 22,
It is connected between the emitter and collector of the transistor 24, the collector of the constant current source transistor 2o, and the input terminal P4. On the other hand, the emitter of the PNP transistor 27 is connected to the collector of the transistor 2o, a resistor 26 is connected between the base and the input terminal P4, and the collector is used as a constant voltage output terminal P5.
It has a configuration in which a reversely connected Zener diode 3o and a capacitor 29 are connected between the input terminal P4 and the input terminal P4.

According to the circuit of this embodiment, a voltage is applied between the input terminals P and -P4, and the resistor 21 has a voltage of 0. PN when TV voltage is generated
P transistor 33 enters the active region and becomes Y as shown in FIG.
As shown in the L-IL characteristic 11b, a characteristic shown by a polygonal line appears on the low current side.

Effect of the invention when the transistor 33 is in the cutoff region According to the present invention, by providing a current bypass circuit connected to a constant current source, it is possible to cope with an increase in line current with a low line voltage while satisfying the DC impedance standard. The vL-IL characteristics can be freely set.

This makes it possible to use it even in processes with low breakdown voltages.

In the present invention, the characteristic impedance is also sufficiently high, and Ω does not drop to the standard 2. Further, since the current mirror ratio N in the constant current source can be set small, there is an advantage that the element area can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of a telephone, Fig. 2 is a DC characteristic diagram required for a telephone, Fig. 3 is a block diagram of a conventional example of a power supply circuit for a communication circuit, and Fig. 4 is shown in Fig. 3. FIG. 5 is a block diagram of a power supply circuit for a telephone communication circuit according to the present invention, and FIG. 6 is a circuit diagram of a power supply circuit for a telephone communication circuit according to an embodiment of the present invention. p3. p, ...input terminal, P5 ......
Constant voltage output terminal, 1, 2...Line, 3...
...Diode bridge, 6...Telephone circuit, 7
~10.11&, 11kl... vL-machining characteristic straight line, 12... Constant current source, 13...
Electronic switch, 16... Comparison control circuit, 14...
...Reverse current prevention circuit, 15... Constant voltage circuit,
19,20゜24.27.33...PNP transistor, 18゜29...capacitor, 21,
22, 26, 32...Resistor, 30...Zener diode, 31. Old...Current bypass circuit. Figure 1 Kan 2 figure f (mA)
5L-1----L-----+-J
Ward 1 Ma)
6ε Ward 1 1 ℃
1gu u
j time
Castle L-J

Claims (1)

[Claims] One end of the constant current circuit connected between the input terminals is connected in parallel with an electronic switch for lowering the saturation voltage, a comparison control circuit that generates a signal to drive the electronic switch, a backflow prevention path, and a constant voltage circuit. 1. A power supply circuit for a telephone communication circuit, comprising a constant voltage output terminal at a connection point between the prevention circuit and the constant voltage, and a current bypass circuit comprising a transistor and a resistor for the constant current source.