JPH0455016B2 - - Google Patents

Description

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

Conventional configuration and its problems Figure 1 shows a schematic configuration of a telephone. P1 and P2 are external terminals of the telephone, and are input terminals that are connected to the telephone line from the central office and receive DC voltage and receive signals through lines 1 and 2. It is also an output terminal that is sent out through. The input terminals of the diode bridge 3 are connected to the external terminals P1, P2, and the output terminals of the diode bridge 3 are connected to the input terminals P3, P4 of the communication circuit block 6 via internal lines 4, 5. Even if the polarity of the DC voltage applied to the external terminals P1 and P2 is reversed, a positive voltage is applied to the input terminal P3 and a negative voltage is applied to the input terminal P4.

Next, a conventional power supply circuit for a telephone communication circuit will be explained using FIG.

As shown in FIG. 2, transistors 7 and 8 are
The emitters are both connected to the input terminal P3, and the bases are also commonly connected to form a current mirror circuit. A diode-connected transistor 7 is an input means of the current mirror circuit, and resistors 9 and 10 are connected in series between the base of the transistor 7 and the input terminal P4. Determine the current to be applied to the input means. resistance 9,
A capacitor 11 is connected between the connection point 10 and the input terminal P3, and the series circuit of the resistor 10 and the capacitor 11 is for determining the AC characteristic impedance between the input terminals P3 and P4. Further, the common emitter connection point of transistors 12 and 13 is connected to the collector of transistor 8, the base of transistor 12 is connected to the connection point of resistors 9 and 10, the collector is connected to input terminal P4, and the collector of transistor 8 is connected to the connection point of resistors 9 and 10. - The emitter voltage is set to a predetermined voltage determined by the resistance division ratio of the resistors 9 and 10 by the emitter potential of the transistor 12.
Another role of the transistor 12 is to
This is to bypass the collector voltage of the transistor 8, which has become excessively supplied to the constant voltage circuit including the transistor 13, to the input terminal P4. Transistor 13, whose base is connected to input terminal P4 via resistor 14, supplies current to a parallel circuit of Zener diode 15 and smoothing capacitor 16, and the parallel circuit outputs a stabilized voltage to output terminal P5. The voltage at the output terminal P5 of the transistor 13 may be close to the voltage at the input terminal P3 depending on the mode of circuit operation, and the charge in the smoothing capacitor 16 is discharged through the path of the transistors 8, 7 and the resistors 9, 10. This is to prevent A power supply terminal of an electronic circuit such as an amplifier for a communication circuit is connected between the output terminal P5 and the input terminal P4 (not shown).

Here, considering the AC characteristic impedance between the input terminals P3 and P4, the impedance between the terminals of the capacitor 11 is almost zero, so the collector current of the transistor 8 is output as DC.
The impedance between the collector and emitter of the transistor 8 becomes infinite, and the characteristic impedance between the input terminals P3 and P4 is determined by the resistor 10.
The characteristic impedance required for the phone is 600Ω
Therefore, considering that other circuits are connected in parallel between input terminals P3 and P4, a resistor of 10
It is desirable that the resistance value is 2KΩ or more.

However, the direct current circuit current IL flowing through the external terminal required for the telephone is 20 mA to 100 mA, and the direct current resistance between the external terminals P1 and P2 is in the range of 50 to 200 Ω. Therefore, the series resistance of resistors 9 and 10 is 2K.
When the resistance value is set to Ω or more, the mirror ratio of the current mirror circuit is set to 20 to 30 times, and the input terminals P3 and P are connected from transistor 8 through transistor 12.
It was necessary to bypass the current between the two. In order to increase the mirror ratio in this way, it is necessary to increase the shape of the transistor 8, which poses a problem in that the chip area increases when such a circuit is integrated into a semiconductor integrated device. Ta.

Purpose of the Invention The present invention solves the above-mentioned problems, configures an excessive current path without increasing the current mirror ratio, maintains the impedance between input terminals at a high characteristic impedance, and maintains the direct current resistance component. The purpose is to provide a power supply circuit that reduces the size of the power supply circuit.

Structure of the Invention The present invention provides a diode bridge 3 that rectifies current supplied from a telephone line and outputs currents of opposite polarity from first and second output terminals; a first output of the diode bridge 3; A current mirror circuit comprising first and second transistors 7 and 8, each having an emitter connected to its end and whose emitter and base are commonly connected to each other, the first transistor 7 serving as an input means; first and second resistors 9 and 10 connected in series between the collector of the transistor and the second output terminal of the diode bridge; an intermediate connection point between the first and second resistors and the diode bridge; a third transistor 17 whose base is connected to the intermediate connection point of the resistor and whose collector is connected to the second output of the diode bridge; , a third resistor 18 connected between the collector of the first transistor 7 and the emitter of the third transistor 17, and the collector of the second transistor and the second output of the diode bridge 3. This is a power supply circuit for a telephone call circuit, which is equipped with a constant voltage circuit 15 that outputs a constant voltage and is connected between the first output terminal P3 and the second output terminal P4 of the diode bridge. Even if an alternating current signal is superimposed between the third transistor 1 and the
7 operates with the direct current determined by the third resistor 18, the input current of the current mirror circuit can be set to a large value without reducing the resistance values of the first and second resistors. There is no need to increase the mirror ratio.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to a power supply circuit diagram for a telephone communication circuit shown in FIG. Note that the same numbers are given to the same parts as in FIG. 2, and the explanation is omitted.

As shown in FIG. 3, the present invention differs from the conventional example in that the base of the third transistor 17 is connected to the intermediate connection point between the first resistor 9 and the second resistor 10, and its emitter and A third resistor 18 is connected between the collector of the first transistor 7 and the collector of the transistor 17 is connected to the second output terminal (input terminal P4) of the diode bridge 3.

In such a configuration, since the voltage between the terminals of the capacitor 11 is averaged and becomes a DC voltage, the DC current bus determined by the resistor 18 of the transistor 17 is
It is configured between the input means 7 of the current mirror circuit and the second output terminal (input terminal P4) of the diode bridge 3, and the input current of the current mirror circuit can be set to a large value, and the impedance of the collector circuit of the transistor 17 is infinite in AC terms and has a low resistance value in DC terms, so there is no need to increase the mirror ratio of the current mirror circuit. Also, resistance 9,
By selecting the resistance value of the resistor 18, the DC resistance between the telephone lines can be set independently of the characteristic impedance.

Effects of the Invention As explained above, according to the present invention, the voltage between the terminals of the capacitor is averaged to become a DC voltage, so that the DC current path is connected to the input means of the current mirror circuit and the second output of the diode bridge. The input current of the current mirror circuit can be set to a large value without reducing the resistance value of the series circuit of the first and second resistors, increasing the mirror ratio of the current mirror circuit. The need disappears. Further, by selecting the resistance values of the first and second resistors, the DC resistance between the telephone lines can be set independently of the characteristic impedance.

If the circuit of the present invention is integrated, a semiconductor integrated device with a small element area and low cost can be realized.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a telephone, FIG. 2 is a configuration diagram of a conventional power supply circuit for a telephone communication circuit, and FIG. 3 is a configuration diagram of a power supply circuit for a telephone communication circuit according to an embodiment of the present invention. P1, P2...External terminal, P3, P4...Input terminal, P5...Output terminal, 1, 2...Line, 3...
...Diode bridge, 4, 5... Output terminal of diode bridge, 7,, 8, 12, 13... Transistor, 9, 10, 14... Resistor, 11, 16
... Capacity, 15 ... Low voltage element (Zener diode).

Claims (1)

[Claims] 1. A diode bridge that rectifies current supplied from a telephone line and outputs currents of opposite polarity from first and second output terminals, a first output terminal of the diode bridge; A current mirror circuit comprising first and second transistors whose emitters are connected and whose emitters and bases are commonly connected to each other, the current mirror circuit having the first transistor as an input means, the collector of the first transistor and the diode. first and second resistors connected in series between the second output terminal of the bridge, and between the intermediate connection point of the first and second resistors and the first output terminal of the diode bridge; a third transistor whose base is connected to the intermediate connection point of the resistor and whose collector is connected to the second output of the diode bridge; the collector of the first transistor and the third transistor;
a third resistor connected between the emitter of the transistor; and a constant voltage circuit connected between the collector of the second transistor and the second output terminal of the diode bridge and outputting a constant voltage. A power supply circuit for telephone call circuits equipped with