JPH0681176B2 - Power circuit for telephone communication circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit for an electronic telephone communication circuit that can be easily integrated on the surface of one semiconductor substrate.

2. Description of the Related Art FIG. 4 shows a simplified configuration of an electronic telephone. Terminals P ₁ and P ₂ are input / output terminals of a telephone connected to the central office through a line. Phone between input and output terminals P ₁ -P ₂ of a DC voltage and the received signal on lines from the central office is sent, also, the voltage audio signal into a DC voltage by sending a transmission signal on lines from the telephone is superimposed Is applied. Therefore, assuming that the voice signal is v _L sin wt, the terminals P ₁ -P ₂
A voltage in which the AC signal v _L sin wt is superimposed on the DC voltage V ′ _L is applied between them, and the AC current i _L sin is applied to the DC current I _L.
The current with wt superimposed flows in. Between input and output terminals P ₃ -P ₄ of speech circuit 6 V _{L +} v _L sin wt minus the voltage drop of the diode bridge 3 is applied.

DC characteristics (V _'L required of the phone in FIG. 5, _V L -I
_L ) is shown. In the usual case, the line current I _L by conditions such as resistance of the line varies from 20MA～100mA. For example, according to Nippon Telegraph and Telephone Public Notice No. 149, Article 18, the DC resistance of the telephone is specified to be 50Ω or more and 220Ω or less.
This range is shown by broken lines 7 and 8 in FIG. It is a region in which the range of the DC characteristic V _L -I _L acceptable voltage drop of the diode bridge 3 to the speech circuit 6 as 1.4V is surrounded by a solid line 9 and 10. One conventional example of the DC JP characteristic V _L -I _L of speech circuit 6 to enter this area 11a, an example of the present invention
Shown at 11b.

Also, according to Nippon Telegraph and Telephone Public Notice No. 149, Article 19, the characteristic impedance of the telephone is specified as 600Ω. In order to realize this characteristic impedance, it is desirable that the characteristic impedance v _L / i _L of the communication circuit is 2 KΩ or more in consideration of connecting other circuits in parallel with the communication circuit 6.

Next, voice transmission signals and DTMF (Dual Tone Multi Frequency)
ncy) signal transmission level, v _L ≧ 3.0V _PP , THD
It is necessary to satisfy (distortion rate) ≦ 3%. According to FIG. 5, when I _L = 20 mA, OV <V _L ≦ 3 V is specified, but it is desirable that V _L is high in order to secure the above-mentioned v _L transmission level, and in general I _L = When 20mA, V _L =
Set to 2.7V to 3V. Below, V when I _L = 20mA
_The description will be made assuming that _L = 3V.

Generally, in the electronic communication circuit 6, when the AC signal v _L sin wt is superimposed on V _L = 3V, the DC current I _{L stops} flowing at a certain momentary voltage, so that the AC signal voltage is clipped and the waveform is changed. Distorted. The voltage at which the direct current I _L does not flow is called the saturation voltage V _L (sat). v _L
To satisfy ≧ 3 V _PP and THD ≦ 3%, V _L (sat) ≦ 1.
Must be 5V.

The characteristics described so far are characteristics that must be guaranteed by the power supply circuit in the communication circuit 6, and will be summarized below.

Conditions DC resistance: When _{I L = 20mA V L ≦ 3V} I L = 3.6V ≦ V L ≦ 20.6V conditions characteristic impedance when _{100mA: v L / i L ≧} 2KΩ condition _{V L} (sat) ≦ 1.5V above A conventional example satisfying the three conditions will be described.

Nippon Telegraph and Telephone Public Corporation "Research Practical Use Report" Vol. 33, No. 6, P137
~ P151 and 1st Annual Conference of IEICE General Conference No. 22.6
No. 6 of the block diagram of the conventional speech circuit reported in 5
FIG. 7 shows an example of the circuit. In the sixth figure, the constant current circuit 12 is set to have a satisfying DC characteristics (V L _{-I L),} the DC current I _L is supplied to the constant voltage circuit 15 through the discharge prevention circuit 14, the terminal P DC voltage between _{5 and} P ₄
V ₀ occurs. This DC voltage V ₀ is generally V ₀ = 1.7V
It is set to about 2V and used as a voltage source for driving the speech circuit. Electronic circuit to meet the conditions 13
And the comparison control circuit 16. Now, electronic switch circuit 13
Removed from the circuit, by applying a DC voltage V _L across the terminals P ₃ -P _4, the direct current I when went down the DC voltage V _L
L is the voltage of becomes _{V L} does not flow to the V _sat.

When V _L + v _L sin wt ≧ V _sat , the electronic switch 13 is opened, and the direct current I _L becomes the discharge prevention circuit 14 and the constant voltage circuit 15.
Through the common terminal P ₄ .

When V _L + v _L sinωt <V _sat , the electronic switch 13 is closed and the direct current I _L is passed through the electronic switch 13 to the common terminal P ₄ . During this time, the output voltage V ₀ of the constant voltage circuit 15 is maintained at a predetermined terminal voltage V ₀ by the capacitor C2, and the operation of the communication circuit is maintained. In this way, the direct current I _L
Is kept constant even when the AC signal v _L sin wt is applied,
The condition is realized.

Problems to be Solved by the Invention However, according to the conventional example, the first problem is that V _L −
There is no freedom in setting the _IL characteristics.

For simplification of description, it is assumed that the base-emitter voltage V _{BE in} the active region of each transistor is V _BE = 0.7 V and the direct current amplification factor h _fe = ∞. Although it is possible to explain in consideration of accurate V _BE and h _fe , it does not affect the explanation of the basic operation, so that it will be explained with the above V _BE = 0.7 V, h _fe = ∞. The DC characteristics of the conventional example will be described with reference to FIG. Between the terminals P ₃ -P _4, when the DC voltage V _L is applied, current begins to flow through the PNP transistor Q1 when V L ₌ 0.7 V. Same as PNP transistor Q1 Q2
If the ratio of the emitter area to and is 1: N, PNP transistor Q2
N of collector current of PNP transistor Q1
A double current flows, and I _L can be expressed as follows.

When the required DC characteristics of I _{L =} 20 mA, and V L ₌ 3V, when a typical value is substituted for N = 20 in equation (1),
R ₁ + R ₂ is given by the following equation.

For _{R 1 + R 2 = 2.3KΩ ......} (2) the capacitor C1 is set to a sufficiently low impedance to AC, the characteristic impedance viewed from the terminal P ₃ is equal to or less than 2.3Keiomega. Further, the characteristic impedance seen from the terminals P _{3 to} P ₄ is further lowered by the Early effect of the PNP transistor Q2. In order to avoid a decrease in the characteristic impedance due to the value of the resistor R2, it is necessary to set N large, resulting in an increase in the element area of the PNP transistor Q2. When I _L = 100 mA, the DC voltage V _L is automatically determined, and V _L = 11.7V. Thus I _L = 100mA
Since the value of the DC voltage _VL at the time of cannot be set freely,
It becomes necessary to adopt a high withstand voltage process. The DC characteristics of this conventional circuit are shown by the solid line 11a in FIG.

Next, as a second problem, it is necessary to consider a decrease in characteristic impedance due to the Early effect of the PNP transistor Q2.

In FIG. 7, when the electronic switch 13 is opened, an AC voltage v _L sin is applied between the emitter and collector of the PNP transistor Q2.
Since it is shaken by wt, i ₁ sin due to the Early effect
wt flows.

Generally, the collector current I _C of the PNP transistor Q2 is expressed by the following equation.

However, V _CE is the collector-emitter voltage V _A is the early voltage I _CO is the collector current I _C when V _CE = 0 obtained by removing the I _C -V _CE characteristic.

From the equation (3), the AC impedance v _L / i ₁ between the collector and the emitter of the PNP transistor Q2 is expressed by the following equation.

In order to make the characteristic impedance seen from the terminals P ₃ -P _{4 2} KΩ or more, it is necessary that v _L / i ₁ ≧ 2 KΩ. v _L / i ₁ ≧
Substituting ₂ KΩ and I _CO I _C = 100 mA into the equation (4), the early voltage V _A becomes the following equation.

V _A ≧ 200V ...... (5) i.e., using the conventional circuit of FIG. 7, when the characteristic impedance seen from the terminal P ₃ -P ₄ of I _{L =} 100 mA, the PNP transistor Q2 when you try to more 2KΩ The early voltage V _A needs to be V _A ≧ 200V. However, the Early voltage of an integrated circuit PNP transistor is generally V _A = 50
It is ˜100 V, and the conventional circuit cannot achieve the characteristic impedance v _L / i _L ≧ 2 KΩ seen from the terminals P ₃ -P ₄ .

A third problem is that the discharge of the capacitor C2 by the reverse transistor of the PNP transistor Q4 cannot be ignored.

FIG. 8 shows the voltage waveform of each node when the conventional circuit of FIG. 7 operates at I _L = 20 mA, V _L = 3 V, v _L = 3 V _PP .
Solid lines 16, 17, 19 and 20 are V _L + v _L sin wt, PNP respectively
Base voltage V _{B 3} of transistor Q3, PNP transistor Q2
Is the collector voltage V _{C 2} , the output voltage V _0, and the base voltage V _{B 4} of the PNP transistor Q4. In the operation example of FIG. 8, the saturation voltage of each transistor is 0.2 V, the base-emitter voltage in the active region is 0.7 V, and the Zener diode is
The Zener voltage of Z1 was set to 2V. The period of t ₁ is V _{B 3} > B _B
4 , the current of the PNP transistor Q2 in the constant current source 12 is supplied to the Zener diode Z1 through the PNP transistor Q4 in the discharge prevention circuit 14, and the output voltage V ₀ of the constant voltage circuit 14 is output to the terminal P ₅ . The period of t ₂ is V _{B 3} <V _{B 4} , and
The collector current of PNP transistor Q2 is PNP transistor Q3
Is bypassed to terminal P ₄ through and prevents AC waveform clipping at terminal P ₃ . In FIG. 8, a period t ₃ is a period in which the emitter voltage of the PNP transistor Q4 is lower than the collector voltage and the PNP transistor Q4 operates as a reverse direction transistor. Therefore the charge accumulated in the capacitor C2 is rapidly discharged through the PNP transistor Q4 and Q3 to terminal P _4, occurs inconvenience that ripple ride V _0.

Problems to be Solved by the Invention The present invention has the above-mentioned problems V _L- I _L characteristics cannot be set freely, the characteristic impedance is lowered due to the Early effect, and the problem is due to the reverse transistor of the PNP transistor Q4. The present invention has been made in view of discharge of the capacitor C2 and the like, and provides a power supply circuit of a telephone call circuit for an electronic telephone, which is easily integrated into a semiconductor.

Means for Solving the Problems An outline of the present invention is shown. It has an input terminal for power supply and signal input / output, a common terminal, and a constant voltage output terminal for driving a circuit, and an input terminal and a constant voltage output terminal. In the circuit in which the constant current circuit and the discharge prevention circuit are connected in series between and the electronic switch is connected between the discharge prevention circuit connection point side of the constant current circuit and the common terminal, the constant current circuit and the common terminal A current bypass circuit is connected between the input terminal and the common terminal, and a bias circuit and a comparison control circuit are connected in series between the input terminal and the common terminal.A current signal for controlling the opening and closing of the electronic switch and the discharge prevention circuit. And a constant voltage circuit for converting the voltage applied to the constant current circuit to a DC voltage between the constant voltage output terminal and the common terminal, and the signal for driving the comparison control circuit is a constant current circuit and Constant voltage output It is a power supply circuit of a telephone call circuit characterized by being supplied from a power terminal.

Action The action of the present invention will be described. When a DC voltage is applied to the input terminal, the
It can be freely set the inclination of the point A and _V L -I _L characteristics of Fig. Next, when a voltage in which an AC voltage is superimposed on a DC voltage is applied between the input terminal and the common terminal, the PNP transistor in the constant current circuit and discharge prevention circuit saturates, and there is a period when current does not flow to the constant voltage circuit. Occurs. During that time, the current passes through the electronic switch and is bypassed to the common terminal, preventing clipping of the AC waveform. Moreover, by utilizing the Early effect of the PNP transistor used in the constant current circuit, the characteristic impedance seen from the input terminal is prevented from decreasing.

EXAMPLES Next, the present invention will be described with reference to Examples.

FIG. 1 is a block diagram of a circuit of an embodiment of the present invention, and FIG. 2 is a detailed circuit diagram. FIG. 3 is a characteristic diagram of the circuit according to the embodiment of the present invention.

The constant current circuit 17 is a PNP transistor Q in the circuit of FIG.
5 and an emitter connected to the Q6 to the input terminal P _3, a base connected to the collector and base and PNP transistor Q6 of PNP transistors Q5, the collector of the PNP transistor Q5 and a resistor R4 between the common terminal P ₄ equal R5 is connected in series, input terminal
It has a configuration in which a capacitor C ₃ for bypassing an AC signal is connected between P ₃ and the connection point of the resistance R 4 on the resistance R 5 side, and the connection point of the electronic switch 21 and the discharge prevention circuit 22 from the collector of the PNP transistor Q 6 Supply a constant current to.

The electronic switch 21 is composed of a PNP transistor Q19,
The discharge prevention circuit 22 is composed of a PNP transistor Q20. The emitters of the PNP transistors Q19 and Q20 are connected in common and connected to the collector of the PNP transistor Q6 of the constant current circuit 17. The bases of the PNP transistors Q19 and Q20 are the bias circuit 19 together with the comparison control circuit 20.
The collectors of the PNP transistors Q19 and Q20 are connected to the common terminal P ₄ and the constant voltage output terminal P ₅ , respectively.

The constant voltage output circuit 23 has a configuration in which a Zener diode Z2 and a capacitor C4 are connected in parallel, the anode of the Zener diode Z2 is connected to the common terminal P ₄ , and the cathode is connected to the constant voltage output terminal P ₅ .

The current bypass circuit 18 has a configuration in which the resistor R6 is connected to the emitter of the PNP transistor Q7, the other end of the resistor R6 is connected to the collector of the PNP transistor Q7 of the constant current circuit, and the collector of the PNP transistor Q5 is the common terminal P ₄ The base is resistance
It is connected to the common connection point of R4 and R5.

The comparison control circuit 20 includes a PNP transistor Q10 which is a constant current source and PNP transistors Q11, Q12, Q13 and Q14 which form a comparator.
And NPN transistors Q15 and Q1 that form a Karen mirror
6, Q17, Q18 and is composed of a resistor R9, R10 for bias adjustment, the emitter input terminal P ₃ of the PNP transistor Q10, the base is the base of the PNP transistor Q5 of the constant current circuit 17, the collector The emitters of PNP transistors Q11 and Q12 are respectively connected, the collectors of PNP transistors Q11 and Q12 are respectively connected to the collectors of NPN transistors Q15 and Q16, and the bases of PNP transistors Q11 and Q12 are PNP transistors respectively. Q13 and Q
PNP transistor Q13 and Q1 connected to the emitter of 14
The collectors of 4 are both connected to the common terminal P ₄ , the base of the PNP transistor Q13 is connected to the common connection point between the resistors R4 and R5 of the constant current circuit, and the base of the PNP transistor Q14 is connected to the resistor R9 for bias adjustment. is connected to the common connection point of the R10, the resistor R9 for bias adjustment R10 are connected in series between the constant voltage output terminal R ₅ and the common terminal P _4, NPN transistor Q15 constituting a current mirror, The emitters of Q16, Q17, and Q18 are all connected to the common terminal P ₄ , and the NPN transistor Q
For 15, Q16, the base and collector are connected in common,
The collectors of NPN transistors Q15 and Q16 are connected to the collectors of PNP transistors Q11 and Q12, respectively, and the bases of NPN transistors Q17 and Q18 are NPN transistors Q16 and Q15, respectively.
Of the NPN transistors Q17 and Q18 are connected to the bases of PNP transistors Q20 and Q19, respectively.

The bias circuit 19 is commonly connected to respective collectors of the Q9 and the NPN transistor Q8, the diode D1 to a resistor R7 connected in series R8 and the input terminal R ₃ side and the anode between an input terminal P ₃ and the connection point Connect and NPN transistors Q8 and Q9
Connect the bases of both to the common connection point of resistors R7 and R8, and
The emitters of N transistors Q8 and Q9 are connected to the bases of PNP transistors Q19 and Q20, respectively.

The operation of the present invention will be described with reference to FIG.

When applying a DC voltage _{V L} to the terminal P _3, V L -I _L characteristic is as follows.

An example of the V _L -I _L characteristic represented by the equations (5), (6) and (7) is shown by the solid line 11b in FIG. The point A on the solid line 11b is Is the point where the V _L -I _L characteristic is a polygonal line.
Point A is R ₅ / R ₄ , At this time, the slope of the V _L -I _L characteristic can be freely set by R ₄ / R ₆ .

As a result, the first problem of the conventional circuit can be easily solved,
In addition, the resistance R5 can be set sufficiently higher than 2KΩ so that the characteristic impedance (v _L / i _L ) seen from the terminals P ₃ -P _{4 is} not reduced, and the emitter area ratio N of the transistors Q5 and Q6 is set small. Therefore, there is an advantage that the element area can be reduced.

Next, the AC characteristics will be described.

When the DC voltage V _L to the voltage superimposed on an AC voltage v _L sin wt is applied to the terminals P ₃ -P _4, the PNP transistor Q20 is saturated constant voltage of PNP transistor Q6 and the discharge preventing circuit of the constant current circuit There is a period in which no current flows in the circuit 23. FIG. 3 shows the potential of each node in the circuit of FIG. 2 when the saturation voltage of each transistor is assumed to be 0.2V and V _L = 3V and v _L = 3V _PP . . In the figure, the period of t ₂ is a constant voltage circuit
This is the period when no current flows to 23. During the period of t _2, the current is bypassed to the terminal P ₄ through the PNP transistor Q19 of the electronic switch. In this way, AC waveform clipping is prevented. At this time, by cutting off the base current of the PNP transistor Q20, the PNP transistor Q20 is prevented from acting as a reverse direction transistor. Period t ₁ during the period t ₂ PNP transistor Q20 is closed so PNP transistor Q19 is closed, as shown in solid lines 26 and 27 of FIG. 3, to adjust the input of the comparator control circuit 20. As described above, the third problem of the conventional circuit is solved.

The bias circuit solves the second problem. A constant voltage is generated by the diode D1 of the bias circuit, the voltage is divided by the resistors R7 and R8, and the emitter follower
The voltage is output at Q8 and Q9 and is input to the electronic switch 21 and the discharge prevention circuit 22, respectively. As a result, as shown by the solid line 25 in FIG. 3, the potential between the collector and the emitter of the PNP transistor Q6 of the constant current circuit is kept constant and the Early voltage is equivalently increased. By this,
Terminals P ₃ -P ₄ due to the Early effect of PNP transistor Q6
This prevents the characteristic impedance from being impaired.

In the circuit of FIG. 2, R4 = 8.2KΩ, R5 = 10KΩ, R6 = 620
Ω, R7 = 4.3KΩ, R8 = 3KΩ R9 = 15.4KΩ, R10 = 10KΩ, C3 = 2
2μF, C4 = 47μF, Z2 zener voltage = 2V, Q5 and Q6 emitter area ratio was set to 1:24. As a result, V _L −I _L
Characteristics obtained solid 11b of FIG. 5, a 5KΩ characteristic impedance I _{L =} 100 mA viewed from the terminal P3, V L _(sat)
= 1V, and good results were obtained in which V ₀ was not reduced by the discharge prevention circuit.

Effects of the Invention According to the present invention, the following effects are noticeable.

V _L -I _L characteristic can freely set, it may be employed low-voltage process of.

A high characteristic impedance can be easily realized.

The ripple due to the AC signal at the constant power output terminal can be reduced, and a stable power supply can be obtained.

When integrated with a semiconductor, it can be made into a smaller chip than a conventional circuit.

A rational circuit can be constructed by taking comprehensive measures against the three problems.

[Brief description of drawings]

FIG. 1 is a block diagram of a power supply circuit of a telephone circuit of the present invention, FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIG. 3 shows voltage waveforms of main nodes of the embodiment of the present invention. 4 and 5 are schematic configuration diagrams of a telephone, FIG. 5 is a diagram showing direct current characteristics required for a telephone and a call circuit, and FIG. 6 is a block diagram of a conventional example of a power supply circuit of the call circuit, and FIG. 6 is a circuit diagram of the block diagram shown in FIG. 6, and FIG. 8 is a diagram showing voltage waveforms of main nodes of the circuit of FIG. P ₁ , P ₂ …… Telephone input terminal, P ₃ …… Call circuit input terminal, P ₄ …… Call circuit common terminal, P ₅ …… Constant voltage output terminal, 1, 2 …… Line, 3… … Diode bridge, 6 ……
Call _{circuit, 7,8,9,10,11a, 11b ...... V L (} V 'L) -I L
Characteristic straight line, 13,21 …… Electronic switch, 14,22 …… Discharge prevention circuit, 15,23 …… Constant voltage circuit, 16,20 …… Comparison control circuit, 12,17 …… Constant current circuit, 18… … Current bypass circuit, 1
9 …… Bias circuit, 24,25,26,27 …… Voltage waveform, C1, C2,
C3, C4 …… Capacitor, R1 to R10 …… Resistance, Z1, Z2 …… Zener diode, D1 …… Diode, Q1, Q2, Q3, Q4, Q
5, Q6, Q7, Q10, Q11, Q12, Q13, Q14, Q19, Q20 …… PNP transistor, Q8, Q9, Q16, Q17, Q18 …… NPN transistor.

Claims (7)

[Claims] 1. A constant current circuit and a discharge prevention circuit are connected in series between the input terminal and the constant voltage output terminal, and the constant voltage output is provided. A constant voltage circuit is connected between the terminal and the common terminal, and an electronic switch is connected between the discharge prevention circuit side connection point of the constant current circuit and the common terminal, and
A current bypass circuit is connected between the constant current circuit and the common terminal, and a current signal for controlling opening and closing of the electronic switch and the discharge prevention circuit is generated between the input terminal and the common terminal. A telephone having a comparison control circuit and a bias circuit for changing the voltage applied to the constant current circuit to a DC voltage, and the constant current circuit and the constant voltage output terminal being connected to the comparison control circuit. Power supply circuit for the call circuit. 2. A first PNP transistor, wherein each emitter of the first and second PNP transistors is connected to an input terminal, and the collector and base of the first PNP transistor and the base of the second PNP transistor are connected. The first and second resistors are connected in series between the collector and the common terminal of the
A configuration in which a first capacitor for AC bypass is connected between the connection point between the first and second resistors, and the collector of the second PNP transistor is connected to a common connection point of the electronic switch and the discharge prevention circuit. The power supply circuit of the telephone communication circuit according to claim 1, comprising the constant current circuit of claim 1. 3. An electronic switch and a discharge prevention circuit are constituted by third and fourth PNP transistors having a common emitter, and the emitter is connected to the collector of the second PNP transistor of the constant current circuit, and the third The bases of the fourth PNP transistor are connected to a comparison control circuit and a bias circuit, respectively, and the collectors of the third and fourth PNP transistors are connected to a common terminal and a constant voltage output terminal, respectively. A power supply circuit for a telephone communication circuit according to claim 1. 4. A constant voltage circuit comprising a parallel circuit of a zener diode and a capacitor, wherein the zener diode has an anode connected to a common terminal and a cathode connected to a constant voltage terminal. The power supply circuit of the telephone communication circuit described in the item. 5. An emitter of a fifth PNP transistor is connected to a third resistor, and the other end of the third resistor is connected to the collector of the first PNP transistor in the constant current circuit. The power supply circuit of the telephone call circuit according to claim 1, further comprising a current bypass circuit having a structure in which the base is connected to the connection point of the first and second resistors. 6. A seventh, an eighth, a ninth and a tenth PNP transistors forming a so-called comparator together with a sixth PNP transistor and first, second, third and fourth forming a so-called current mirror. 4th for NPN transistor and bias adjustment,
A fifth resistor, the emitter of the sixth PNP transistor is used as an input terminal, the base is used as the base of the first PNP transistor of the constant current circuit, and the collector is used as the seventh,
Connected to the emitter of the eighth PNP transistor,
The collectors of the eighth PNP transistors are respectively
Connected to the collectors of the first and second NPN transistors,
7, the base of the 8th PNP transistor is respectively the 9th,
Connected to the emitter of a tenth PNP transistor,
The collectors of the tenth PNP transistor are both connected to a common terminal, the base of the ninth PNP transistor is connected to the connection point of the first and second resistors of the constant current circuit, and the tenth PN transistor is connected.
The base of the P-transistor is connected to the common connection point of the fourth and fifth resistors for bias adjustment, the fourth and fifth resistors are connected in series between the constant voltage output terminal and the common terminal, and The emitters of the first, second, third and fourth NPN transistors forming a current mirror are connected to a common terminal, the bases and collectors of the first and second NPN transistors are commonly connected, and the first The collector of the second NPN transistor is connected to the collectors of the seventh and eighth PNP transistors, and the bases of the third and fourth NPN transistors are respectively connected to the bases of the first and second NPN transistors. Connect and
The power supply circuit for a telephone communication circuit according to claim 1, further comprising a comparison control circuit having collectors respectively connected to the bases of the third and fourth PNP transistors. 7. The sixth and seventh resistors connected in series between the collectors of the fifth and sixth NPN transistors, and the connection point and the input terminal, and a diode having the input terminal side as an anode. And connecting the bases of the fifth and sixth NPN transistors together to a common connection point of the sixth and seventh resistors,
5. The power supply circuit for a telephone communication circuit according to claim 1, further comprising a bias circuit in which the emitters of the fifth and sixth NPN transistors are connected to the bases of the third and fourth PNP transistors, respectively.