JPH02235119A - Power supply circuit - Google Patents

Abstract

PURPOSE:To prevent the generation of abnormal voltage rise at the time of no load and high temperature by separating a Darlington circuit to be a differential amplifier from a differential amplifier circuit through plural current mirror circuits. CONSTITUTION:When a temperature is increased at the time of no load, voltage between the base and emitter of a control transistor(TR) is dropped and the base potential of an npn TR Tr6 of the Darlington circuit 9 to be a differential amplifier is dropped. On the other hand, the base of the TR Tr6 is separated from the collector of a TR Tr3 for inputting the feedback voltage of the differential amplifier circuit 7 through the 2nd and 3rd current mirror circuits 13, 14 and the base potential of the TR Tr6 in the circuit 9 is earthed through at least two TRs TR6, Tr7, a sufficient margin for the potential of the 3rd current mirror circuit 14 earthed through the 1st TR Tr6 is secured, so that the generation of abnormal rise of an output voltage due to the positive feedback of feedback control based upon the differential amplifier at the time of no load and high temperature can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a series control type power supply circuit using a pnp transistor as a series control element.

[Conventional technology]

FIG. 2 shows an example of a series control type power supply circuit using transistors.

This power supply circuit has a pnp connection between the DC power supply 1 and the load 2.
}It is a constant voltage circuit in which the emitter and collector of a control transistor Tr, consisting of a transistor, are connected in series,
As explained below, this control transistor Tr+
A constant output voltage is supplied to the load 2 by controlling the drive current flowing to the base of the load 2.

A resistor R. is connected to the output side of the control transistor Tr+. A voltage dividing resistor circuit 3 consisting of a resistor R2 and a resistor R2 is connected in parallel to the load 2. Then, the resistance R in this voltage dividing resistor circuit 3
1 and resistor R2 is connected to feedback voltage input B in differential amplifier 4. Further, a reference voltage source 5 is connected to a reference voltage input A in the differential amplifier 4. Therefore, in this differential amplifier 4, the reference voltage of the reference voltage source 5 is input to the reference voltage input A, and the feedback voltage obtained by dividing the output voltage of the power supply circuit by the voltage dividing resistor circuit 3 is input to the feedback voltage input B. The difference between the reference voltage and the feedback voltage is amplified and output from the differential amplification output CD. The differential amplification output C-D of the differential amplifier 4 is connected between the base of the control transistor Tr and the protection circuit 6 to control the drive current of the control transistor Trt. ing. Therefore, this power supply circuit negatively feeds back the output voltage of the power supply circuit to the control transistor Tr+, and performs feedback control so that the output voltage supplied to the load 2 is always kept constant as described above. .

The protection circuit 6 includes an overcurrent protection circuit, a short circuit protection circuit, an overheat protection circuit, an overvoltage protection circuit, and the like, and is a circuit for protecting the power supply circuit and the load 2.

The conventional differential amplifier 4 in the above power supply circuit will be explained based on FIG. 3.

The reference voltage input A and feedback voltage input B shown in FIG.
Connected to the bases of r2 and Tr3.

This npn transistor Tr. - Tr3 is a transistor having almost the same characteristics, and its emick is connected to the ground power supply GND via a common emitter resistor R3, and each collector is connected to the first output line 10 and the second output line, respectively.
Connected to output 111. Also, these output lines 1
0.11 is pnp } Runsistor T r a Trs
are connected to the power supply VCC through a current mirror circuit 8 consisting of the following resistors R4 and R5, respectively. As a result, the differential amplifier circuit 7 outputs the difference between the reference voltage input to the reference voltage input A and the feedback voltage input B and the feedback voltage between the output lines 10 and 11, and the differential amplifier 4
constitutes the input stage of

npn transistor Tr in the differential amplifier circuit 7
．． The second output line 11 connected to the collector of the transistor Tr. It is also connected to the base of. This Darlington circuit 9 is a circuit in which two transistors Tra and Tr-r are connected together, and constitutes the output stage of the differential amplifier 4. Then, npn in this Darlington circuit 9
The collector and emitter of the transistor Tr serve as the differential amplification output C-D, respectively. Note that the capacitor C connected between the collector haze of the npn transistor Tr3 in the differential amplifier circuit 7 is an oscillation prevention capacitor.

The operation of the conventional differential amplifier 4 will be explained.

If the output voltage of the power supply circuit drops below a predetermined voltage due to fluctuations in the load 2 shown in FIG. 2, the feedback voltage divided by the voltage dividing resistor circuit 3 will also fall below the reference voltage of the reference voltage source 5. . Then, in the differential amplifier 4, since the feedback voltage input to the feedback voltage input B becomes lower than the reference voltage input to the reference voltage input A, the np voltage in the differential amplifier circuit 7
n }The current flowing between the collector and emitter of the transistor Tr3 decreases, and the npn in the Darlington circuit 9 decreases.
}Increase the current flowing between the collector and emitter of transistor Tr=. Therefore, since the drive current of the control transistor Trl increases, the output voltage also increases.

Furthermore, if the output voltage of the power supply circuit becomes higher than a predetermined voltage due to a change in the load 2 shown in FIG. 2, etc., the feedback voltage will also rise above the reference voltage. Then, is the differential amplifier 4 a differential amplifier circuit? npn } transistor Tr. The current flowing between the collector and emitter of the npn transistor Try in the Darlington circuit 9 is increased, and the current flowing between the collector and emitter of the transistor Try in the Darlington circuit 9 is decreased. Therefore, the control transistor Tr in FIG.
．． Since the drive current of the motor decreases, the output voltage also decreases. As a result, the differential amplifier 4 uses the control transistor Tr so that the output voltage of the power supply circuit is always kept constant. You can add negative feedback to us.

[Problem to be solved by the invention]

However, when using the differential amplifier 4 shown in FIG. 3 above, there is a problem in that the output voltage of the power supply circuit abnormally increases at no-load high temperature due to a decrease in the base-emitter voltage VSt of the transistor due to temperature rise. was occurring.

That is, the base-emitter voltage v1■ of the transistor has a negative temperature characteristic, and the voltage decreases as the temperature rises. Therefore, when the temperature rises during no-load, this voltage v0 decreases, causing the npro transistor Tr in the Darlington circuit 9 to rise. The base potential of becomes low. However, the feedback voltage input to feedback voltage input B is
Since the potential is maintained at the same potential as the reference voltage of the reference voltage source 5, which is constant regardless of the temperature, when the temperature rise becomes large, this npn} transistor Tr. becomes relatively higher than the base potential of Therefore, the np in the differential amplifier circuit 7
n } transistor Tr, is saturated by applying a forward bias between its base and collector, so that the feedback control by the differential amplifier 4 based on the feedback voltage no longer works.

Also, as mentioned above, npn in the Darlington circuit 9
Transistor Tr. When the base potential of Tr. The drive current will also increase. Then, the output voltage of the power supply circuit increases, and the feedback voltage also increases accordingly, so that the base-collector forward bias voltage of the npn transistor Tr3 further increases. When the forward bias voltage becomes higher in this way, the npn transistor Tr. Current also flows into the Darlington circuit 9 from the feedback voltage input B via the base-collector of the circuit. As a result, when there is no load at high temperature, the feedback control of the control transistor T r 1 by the differential amplifier 4 forms a positive feedback loop, and the output voltage of the power supply circuit changes from the voltage of the DC power supply l to the WII standard transistor. Njista Tr.
This results in an abnormality in which the voltage suddenly rises to the value obtained by subtracting the saturation voltage.

[Means to solve the problem]

In order to solve the above problems, the power supply circuit according to the present invention has the following features:
A differential circuit that outputs the difference between the input voltages of the bases of two transistors between a first output line and a second output line, each of which has one end connected to the power supply via a resistor and the other end connected to each collector. It has a differential amplifier consisting of an amplifier circuit and a Darlington circuit that amplifies the differential output of the differential amplifier circuit using two compositely connected transistors. Input a feedback voltage and a predetermined reference voltage that each change in accordance with the output voltage,
In a power supply circuit that maintains the output voltage at a constant voltage according to a reference voltage by controlling a series control element consisting of a pnp} transistor by the output of the Darlington circuit,
A third output line and a fourth output line are provided, each having one end connected to the power supply via a resistor and the other end grounded, and a first output line in the differential amplifier circuit is connected to the power supply via a first current mirror circuit. the second output line is connected to the third output line via the second current mirror circuit;
The second current mirror circuit of the third output line and the ground are connected via the third current mirror circuit to the first current mirror circuit of the fourth output line and the ground. It is characterized by having a differential amplifier in which the base of the first stage transistor in the Darlington circuit is connected between the current mirror circuit and the third current mirror circuit. [Function] When the reference voltage input to the base of one transistor of the differential amplifier circuit in the differential amplifier matches the feedback voltage input to the base of the other transistor, the voltage of these two transistors The operating states are equal and no differential output appears between the first and second output lines. However, when the feedback voltage becomes higher than the reference voltage,
The current flowing to the second output line increases through the transistor that inputs this feedback voltage. Then, the current flowing to the third output line via the second current mirror circuit increases, and the current flowing to the fourth output line via the third current mirror circuit also increases. However, since the current flowing through the first output line is relatively reduced, the current flowing through the first current mirror circuit into the fourth output line is also reduced. Therefore, in the Darlington circuit connected between these current mirror circuits in the fourth output line, the inflow of current from the first current mirror circuit side is restricted, and the current is drawn out to the third current mirror circuit side. , and the output of the differential amplifier decreases.

Furthermore, when the feedback voltage becomes lower than the reference voltage, the current flowing to the second output line through the transistor that inputs this feedback voltage decreases. Then, the current flowing to the third output line via the second current mirror circuit decreases, and the current flowing to the fourth output line via the third current mirror circuit also decreases. However, since the current flowing in the first output line relatively increases, the current flowing in the fourth output line via the first current mirror circuit also increases. Therefore, in the fourth output line, the current from the first current mirror circuit side is limited by the third current mirror circuit, so the current flowing into the Darlington circuit connected between these current mirror circuits increases, and the differential Improves amplifier output.

As a result, the output voltage is negatively fed back to the series control element of the power supply circuit via this differential amplifier, so that the output voltage can be maintained at a constant voltage according to the reference voltage.

Here, when the temperature rises under no load, the base potential of the first stage transistor in the Darlington circuit decreases due to a decrease in the base-emitter voltage VIIE of the transistor. However, the base of the first-stage transistor in this Darlington circuit and the collector of the other transistor that inputs the feedback voltage in the differential amplifier circuit are separated via a second current mirror circuit and a third current mirror circuit. In addition, the base potential of the first stage transistor in the Darlington circuit is grounded through at least two stage transistors, so at least the voltage
．． It has a potential more than twice that of . On the other hand, the fourth output line side of the third current mirror circuit is grounded through one stage of transistors, and therefore has a potential higher than the voltage V0. Therefore, even if the base potential of the first-stage transistor in the Darlington circuit becomes low at high temperature with no load, there is no fear that current will flow into the Darlington circuit. Therefore, the feedback control by the differential amplifier does not become positive feedback at high temperature with no load, and the output voltage does not rise abnormally.

Further, as described above, the operating point of the third current mirror circuit is lowered and the dynamic range is expanded, so that the ripple removal rate can be improved.

〔Example〕

An embodiment of the present invention will be described below based on FIG.

This embodiment shows the same configuration as the series control type power supply circuit illustrated in FIG. 2 above. This power supply circuit is a constant voltage circuit in which the emitter collector of a control transistor Tr+ consisting of a pnp transistor is connected in series between the DC current -tA1 and the load 2, and the feedback voltage is divided by a voltage dividing resistor circuit 3. A constant output voltage is supplied to the load 2 by amplifying the difference between the voltage and the reference voltage of the reference voltage source 5 by the differential amplifier 4 and controlling the drive current flowing to the base of the control transistor Trl. It has become.

The configuration of the differential amplifier 4 in the power supply circuit of this embodiment is as follows.
This will be explained based on the diagram. For convenience of explanation, the third
Components that have the same functions as the conventional example shown in the figure include:
The same symbols are added.

The reference voltage input A and feedback voltage input B shown in FIG.
It is connected to the base of r t·Tr,1.

The npn } transistors Trz·Tr, are transistors having substantially the same characteristics, and their emitters are connected to the ground power supply GND via a common emitter resistor R,. 20 The collector of the npn transistor Trz in the differential amplifier circuit 7 has one end connected to the power supply V via the resistor Rl+.
It is connected to the other end of the first output line IO connected to CC. In addition, npn } transistor Tr. The collector of
A second terminal whose one end is connected to the power supply VCC via a resistor RI2.
It is connected to the other end of the output line 11. Therefore, this differential amplifier circuit 7 outputs the difference between the reference voltage input to the reference voltage input A and the feedback voltage input B and the feedback voltage between the first output line 10 and the second output line 11. This constitutes the input stage of the differential amplifier 4. Note that this differential amplifier circuit 7 is
A constant current circuit can also be connected in place of the emitter resistor R.

? npn} transistor Tr in the differential amplifier circuit 7
A first output line 10 connected to the collector of z is connected to a fourth output line 16 via a first current mirror circuit 12. Further, a second output line 11 connected to the collector of the npn transistor Tr3 is connected to a third output line 15 via a second current mirror circuit 13. This third output line 15 has one end connected to the power supply VC through a resistor Rlff.
This circuit is connected to C and has the other end connected to a ground power supply GND.

Further, the fourth output line 16 is a circuit in which one end is connected to the power supply VCC via a resistor Rl4, and the other end is connected to the ground power supply GND. And these third output lines l5
and the fourth output line 16 are connected to the ground power supply GND from the second current mirror circuit 13 and from the first current mirror circuit 12 to the ground power supply GND from the third current mirror circuit 1, respectively.
Connected via 4.

The first current mirror circuit 12 includes two pnp transistors Tr. whose bases are connected to each other.・Tr+■
The collector-emitter of the pnp transistor Trll is connected to the first output line 10, and the collector-emitter of the pnp transistor Tr+z is connected to the fourth output line I6. Further, the collector bases of the pnp } transistors Tr, , are connected to each other. Therefore, the fourth output line 16 is connected to the first output line 10 by this first current mirror circuit 12.
A current equal to flows in.

The second current mirror circuit 13 includes two pnp transistors Tr, .
The collector-emitter of the pnp} transistor Trl3 is connected to the second output line 11, and the collector-emitter of the pnp} transistor Trz is connected to the third output line 15. In addition, the collector bases of this pnp transistor TrH are connected. Therefore, the second current mirror circuit 13 causes a current equal to that of the second output line 1l to flow into the third output i15.

The third current mirror circuit 14 includes a resistor RIS and a resistor R.
Two np bases connected to each other via l&
n }Transistor TrH ・Tr. ．． and an npn transistor Tr. , the second current mirror circuit 13 on the third output line 15 is connected between the collector and emitter of
In addition, the collector-emitter of the npn transistor T r r h is connected to the fourth
First current mirror circuit on output line 16. 1 2 is interposed on the ground power supply GND side.

In addition, this npn} transistor Tr. Corctor 5 is connected to the connection point between resistor R+5 and resistor Rl6. Therefore, the third current mirror circuit 14 causes a current equal to that of the third output line I5 to flow through the fourth output line l6. Note that npn in the third current mirror circuit 14
}The capacitor C connected between the collector base of the transistor T r r h is an oscillation prevention capacitor.

The first current mirror circuit 1 in the fourth output line 16
2 and the third current mirror circuit 14, the base of the npn} transistor Tr in the Darlington circuit 9 is connected. This Darlington circuit 9 is a circuit in which two npn transistors Tr6 and Tr6 are connected in a composite manner, and constitutes the output stage of the differential amplifier 4. Then, npn in this Darlington circuit 9
}The collector and emitter of the transistor Tr7 serve as the differential amplification output C-D of the differential amplifier 4, respectively. Note that the npn} transistor Tr in this Darlington circuit 9
．． A resistor Rl? is connected between the emitter of the transistor Tr and the emitter of the transistor Tr? is the bleeder resistance.

The operation of the power supply circuit configured with the differential amplifier 4 as described above will be explained. When the output voltage of the power supply circuit becomes higher than a predetermined voltage due to fluctuations in the load 2 shown in FIG. .

Then, in the differential amplifier 4, the feedback voltage input to the feedback voltage input B becomes higher than the reference voltage input to the reference voltage input A, so that the npn} transistor Tr. The current flowing between collector and emitter increases, and the current flowing through the second output line 1 also increases. Therefore, the third output line 1 is
5 increases, and the current flowing to the fourth output line 16 due to the third current mirror circuit 14 also increases. However, since the current flowing into the first output line 10 through the collector-emitter of the npn transistor Trz in the differential amplifier circuit 7 is relatively reduced, the current flowing into the fourth output line 16 by the first current mirror circuit l2 is also reduced. I will do it. Therefore, the Darlington circuit 9 connected between these current mirror circuits 12 and 14 on the fourth output line 16 is connected to the first current mirror circuit 1.
The inflow of current from the 2nd side is restricted, and the current is drawn to the 3rd current mirror circuit 4 side,
The drive current flowing to the differential amplification output C-D in the differential amplifier 4 is reduced.

Furthermore, when the output voltage of the power supply circuit becomes lower than a predetermined voltage due to fluctuations in the load 2 shown in FIG. become.

Then, in the differential amplifier 4, the feedback voltage input to the feedback voltage input B becomes lower than the reference voltage input to the reference voltage input A. The current that flows decreases, and the current that flows to the second output 41111 also decreases.
Therefore, the second current mirror circuit 13 reduces the current flowing into the third output line 15, and the third current mirror circuit 14 also reduces the current flowing into the fourth output line 16. However, in the differential amplifier circuit 7, the npn} transistor Tr. Since the current flowing into the first output line 10 through the collector-emitter of the first current mirror circuit 12 increases relatively, the current flowing into the fourth output line 16 by the first current mirror circuit l2 also increases. Therefore, in the fourth output line 16, since the increase in current in the first current mirror circuit l2 is limited by the third current mirror circuit 14, the Darlington circuit 9 connected between these current mirror circuits 12 and 14 is The current flowing in increases, and the drive current flowing into the differential amplification output CD in the differential amplifier 4 increases.

As a result, the differential amplifier 4 uses the control transistor Tr shown in FIG. 2 so that the output voltage of the power supply circuit is always kept constant as in the conventional case. It is possible to add negative feedback control to the

Here, when the temperature rises under no load, the base-emitter voltage VIIE of the transistor decreases, causing the npn transistor Tr. The base potential of becomes low. However, the base of this NPN transistor Tr6 and the collector of the NPN transistor Tr3, which inputs the feedback voltage in the differential amplifier circuit 7, are as follows.
They are separated via a second current mirror circuit 13 and a third current mirror circuit 14. Furthermore, the base potential of the npn transistor Trh in the Darlington circuit 9 is
At least two stages of npn transistors Tra and Trv
Since it is grounded via V. It has a potential more than twice that of E. On the other hand, in the third current mirror circuit 14, the npn} transistor Tr. ．． The collectors of the NPN transistors Tr, . Since it is grounded through the voltage ■. It has the above potential. Therefore, due to temperature rise, npn in Darlington circuit 9
}Even if the base potential of transistor Tr. Also, no current flows from the third current mirror circuit 14 side.

Therefore, there is no possibility that the feedback control by the differential amplifier 4 becomes positive feedback and the output voltage abnormally increases at high temperature with no load.

Further, as described above, the operating point of the third current mirror circuit 14 is lowered and the dynamic range is expanded, so that the ripple removal rate can be improved.

〔Effect of the invention〕

As described above, the power supply circuit according to the present invention converts the difference between the input voltages of the bases of the two transistors into the first output line, which has one end connected to the power supply via the resistor and the other end connected to each collector. and a second output line, and a Darlington circuit that amplifies the differential output of the differential amplifier circuit with two compositely connected transistors, In this differential amplifier, a feedback voltage that changes in accordance with the output voltage and a predetermined reference voltage are input to two inputs of the differential amplifier circuit, respectively, and a series control element consisting of a pnp transistor is controlled by the output of the Darlington circuit. In the power supply circuit that maintains the output voltage at a constant voltage according to the reference voltage, a third output line and a fourth output line are provided, each of which has one end connected to the power supply via a resistor and the other end grounded. , the first output line in the differential amplifier circuit is connected to the fourth output line via the first current mirror circuit, the second output line is connected to the third output line via the second current mirror circuit, and the second output line is connected to the third output line via the second current mirror circuit. The second current mirror circuit of the third output line and the ground are connected between the first current mirror circuit of the fourth output line and the ground via the third current mirror circuit, and the first current mirror circuit of the fourth output line is connected between the second current mirror circuit of the third output line and the ground. The configuration includes a differential amplifier in which the base of the first stage transistor in the Darlington circuit is connected between the circuit and the third current mirror circuit.

As a result, the Darlington circuit and the differential amplifier circuit are separated through the two-stage current mirror circuit, and the potential of the input of the Darlington circuit is connected to the third output line connected to the fourth output line.
Have sufficient margin for the potential of the current mirror circuit.
It turns out. This prevents the feedback control by the differential amplifier from becoming positive feedback and causing the output voltage to abnormally increase at high temperatures with no load. Furthermore, the operating point of the third current mirror circuit is lowered and the dynamic range is expanded.

Therefore, the power supply circuit of the present invention has the effect of being able to prevent an abnormal voltage rise at high temperature with no load. Furthermore, by expanding the dynamic range, it is also possible to improve the ripple removal rate.

[Brief explanation of the drawing]

FIG. 1 shows one embodiment of the present invention, and is a circuit diagram of a differential amplifier in a power supply circuit. FIG. 2 is a circuit diagram of the power supply circuit. FIG. 3 shows a conventional example, and is a circuit diagram of a differential amplifier in a power supply circuit. 4 is a differential amplifier, 7 is a differential amplifier circuit, 9 is a Darlington circuit, 10 is a first output line, 11 is a second output line, 12 is a first current mirror circuit, 13 is a second current mirror circuit, 14 is a 3rd current mirror circuit, 15 is the 3rd output line,
16 is a fourth output line, Tr is a control transistor (series control element), Tr2 is an npro transistor (transistor of a differential amplifier circuit), Tr. ．． is npn } transistor (transistor of differential amplifier circuit), Tr= is npn
} transistor (first stage transistor of Darlington circuit C), Tr7 is an npn transistor (transistor of Darlington circuit), RII is a resistor (resistance connected to the first output line), Rl! is the resistance (the resistance connected to the second output line), R+a is the resistance (the resistance connected to the third output line), R
14 is a resistor (resistance connected to the fourth output line), ■. is a power supply, and GND is a ground power supply (ground).

Claims (1)

[Claims] The difference between the input voltages of the bases of one or two transistors is output between a first output line and a second output line, each of which has one end connected to the power supply via a resistor and the other end connected to each collector. It has a differential amplifier consisting of a differential amplifier circuit and a Darlington circuit that amplifies the differential output of the differential amplifier circuit using two transistors connected in a complex manner. By inputting a feedback voltage and a predetermined reference voltage that change in accordance with the output voltage, and controlling a series control element consisting of a pnp transistor by the output of the Darlington circuit, the output voltage is kept constant according to the reference voltage. In the power supply circuit that maintains the voltage, a third output line and a fourth output line are provided, each having one end connected to the power supply via a resistor and the other end being grounded, and a first output line in the differential amplifier circuit is provided. The second output line is connected to the third output line via the second current mirror circuit, and the third output line is connected to the second current mirror circuit and grounded. is connected between the first current mirror circuit of the fourth output line and the ground via the third current mirror circuit, and the fourth
A power supply circuit comprising a differential amplifier in which a base of a first stage transistor in a Darlington circuit is connected between a first current mirror circuit and a third current mirror circuit in an output line.