JP2004062491A - Stabilized dc power supply circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a variance in protective operation characteristic is caused by hfe of a transistor for voltage control in a circuit for detecting the base current of the transistor for the voltage control, controlling the conduction of the transistor for the voltage control and performing protection from overvoltage and load short-circuit. <P>SOLUTION: A stabilized DC power supply circuit is provided with an overcurrent limiting circuit 18 for detecting a main current flowing to the transistor Q11 for the voltage control in a resistor R11 for current detection, controlling the conduction between the output of a differential amplifier 15 and voltage dividing resistors R12 and R13 for voltage detection on the basis of a current flowing to the resistor R11 for the current detection and limiting the current flowing to the transistor Q11 for the voltage control. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a stabilized DC power supply circuit, and more particularly to a stabilized DC power supply circuit having an overcurrent limiting circuit for protecting a voltage control transistor.
[0002]
[Prior art]
A circuit disclosed in Japanese Patent Application Laid-Open No. 2000-187515 (Prior Art 1) will be described with reference to FIG. 2 as an example of a DC stabilized power supply circuit. In the figure, 1 is an input terminal to which an unstabilized DC voltage (input voltage) Vi is supplied, 2 is an output terminal to which a stabilized output voltage Vo is output, 3 is a ground terminal, and Q1 is a PNP type voltage control. In the transistor for use (first transistor), a main current path from the emitter to the collector is connected in series between the input terminal 1 and the output terminal 2. R1 and R2 are voltage detection resistors (first and second resistors) connected in series between the output terminal 2 and the ground terminal 3, 4 is a reference voltage generation circuit for generating a reference voltage Vr, and 5 is a voltage detection resistor. A differential amplifier which receives the voltage Ve of the connection point 6 divided by R1 and R2 and the reference voltage Vr of the reference voltage generation circuit 4 and amplifies the difference voltage, and 7 controls the voltage by the output of the differential amplifier 5 A driver circuit for driving and controlling the transistor Q1. In the example shown in the figure, a third, fourth, and fifth resistors are connected in which the base is connected to the output of the differential amplifier 5, the collector is connected to the input terminal 1, and the emitter is connected in series. A second transistor Q2 grounded via R3, R4, R5, a fourth transistor Q2 having a base connected to the emitter of the second transistor Q2, a collector connected to the base of the voltage controlling transistor Q1, and an emitter diode-connected; The fourth through the transistor Q4, and is constituted by a third transistor Q3 connected respectively to the connection point of the fifth resistor R4, R5. Reference numeral 8 denotes an overcurrent limiting circuit. In the illustrated example, a base is connected to a connection point of the resistors R3 and R4 connected to the emitter of the second transistor Q2 of the driver circuit 7, and the first and second transistors have emitters for voltage detection. And a fifth transistor Q5 connected to a connection point 6 between the resistors R1 and R2, a base connected to the collector of the fifth transistor Q5, an emitter connected to the output of the differential amplifier 5, and a collector grounded. It is composed of a sixth transistor Q6. The second to fifth transistors Q2 to Q5 are of NPN type, and the sixth transistor Q6 is of PNP type. Description of other circuits attached to FIG. 2 is omitted.
[0003]
This DC stabilized power supply circuit amplifies the difference voltage between the reference voltage Vr and the divided voltage Ve appearing at the connection point 6 in proportion to the output voltage Vo of the output terminal 2 by the differential amplifier 5, and the transistor Q2 of the driver circuit 7, By amplifying the current by Q3 and controlling the base voltage of the voltage control transistor Q1, the output voltage Vo can be set to a stable predetermined voltage. On the other hand, when the output current increases, the base current Ib of the voltage control transistor Q1 increases, and the emitter voltage of the transistor Q3 increases. As a result, the base voltage of the transistor Q5 of the overcurrent limiting circuit 8 rises, and the collector and emitter of the transistor Q5 conduct. This lowers the collector voltage, and further lowers the base voltage of the PNP transistor Q6. It conducts and reduces the output of the differential amplifier 5. When the output voltage of the differential amplifier 5 decreases in this way, the base current of the voltage control transistor Q1 is limited through the transistors Q2 and Q3, and this DC stabilized power supply circuit is protected from overcurrent. Further, when the output voltage of the output terminal 2 decreases and a large current flows, for example, when the load is short-circuited, the divided voltage Ve approaches the ground voltage, and the voltage control transistor Q1 sets the output voltage of the differential amplifier 5 to a predetermined value. Attempts to operate to increase the voltage. As a result, the base current of the voltage control transistor Q1 increases, so that the emitter voltage of the transistor Q3 increases. As a result, the transistors Q5 and Q6 are turned on, which lowers the output voltage of the differential amplifier 5 and acts to limit the operation of the voltage control transistor Q1, but further reduces the voltage of the output terminal 2 to a predetermined voltage. Since the divided voltage Ve is reduced to a low voltage close to the ground voltage when the load is short-circuited, as compared with the time of the overcurrent state or the overcurrent state, the voltage between the base and the emitter of the transistor Q5 may be larger than that during the overcurrent limit. As a result, the resistance between the collector and the emitter of the transistor Q5 can be made lower than that at the time of limiting the overcurrent, the output of the differential amplifier 5 can be reduced reliably, and the operation of the voltage control transistor Q1 can be restricted reliably. As shown in FIG. 3, this DC stabilized power supply circuit maintains the rated output voltage V1 from the state where the output current is zero to the rated output current I1, and in the overcurrent state exceeding the rated output current I1, both the output voltage and the output current are slightly increased. The output voltage and the output current decrease when the load that greatly decreases and further exceeds the rated output current I1 is short-circuited, and when the load is short-circuited, the output voltage is close to zero and the output current is reduced to a fraction of the rated output current I1. In other words, the so-called “F” character characteristic is suppressed.
[0004]
FIG. 4 shows a circuit disclosed in Japanese Unexamined Patent Application Publication No. 2-170213 (prior art 2) as another example of a stabilized DC power supply circuit having a square-shaped characteristic. In the drawing, reference numerals 1, 2, and 3 denote input terminals, output terminals, and ground terminals, respectively, Q1 denotes a voltage control transistor, and R1 and R2 denote voltage detection resistors connected in series between the input terminal 1 and the output terminal 2. A main current path from the emitter to the collector of the voltage control transistor Q1 is connected in series, and voltage detection resistors R1 and R2 are connected in series between the output terminal 2 and the ground terminal 3. 4 is a reference voltage generating circuit, 5 is a differential amplifier which receives the reference voltage Vr of the reference voltage generating circuit 4 and the divided voltage Ve divided by the resistors R1 and R2, and outputs an amplified difference voltage. Is a driver circuit for driving and controlling the voltage control transistor Q1 by the output of the differential amplifier 5. In the illustrated example, the base is connected to the output of the differential amplifier 5, the collector is connected to the input terminal 1, and the emitter is connected to the resistor R6. A second transistor Q2 grounded through the third transistor Q2, a base connected to the emitter of the second transistor Q2, a collector connected to the base of the voltage controlling transistor Q1, and a third grounded emitter connected through the resistor R7. It is composed of transistors. Reference numeral 8 denotes an overcurrent limiting circuit. The base is at the emitter of the second transistor Q2 of the driver circuit 7, the collector is at the output of the differential amplifier 5, and the emitter is at the connection point 6 of the first and second resistors R1 and R2. It is composed of seventh transistors Q7 connected to each other. In this circuit, the transistor Q1 is of the PNP type, and the other transistors Q2, Q3, Q7 are of the NPN type. Reference numeral 9 denotes a constant current circuit connected between the input terminal 1 and the output of the differential amplifier 5.
[0005]
This DC stabilized power supply circuit amplifies the difference voltage between the reference voltage Vr and the divided voltage Ve proportional to the output voltage Vo of the output terminal 2 by the differential amplifier 5 and the current amplification by the transistors Q2 and Q3 as in the circuit of FIG. By controlling the base voltage of the voltage control transistor Q1, the output voltage Vo can be set to a stable predetermined voltage. On the other hand, when the output current increases, the base current of the voltage control transistor Q1 increases, the voltage between the terminals of the resistor R7 increases, the emitter voltage of the transistor Q3 increases, and the conduction of the transistor Q3 is limited. When a large current exceeding the value flows, the voltage control transistor Q1 is current-limited. At this time, since the high divided voltage Ve is supplied to the emitter of the transistor Q7 of the overcurrent limiting circuit 8, the transistor Q7 does not conduct. Further, when the input voltage of the driver circuit 7 increases, the output current increases, and an overcurrent state occurs, the emitter voltage of the transistor Q2 further increases. As a result, the transistor Q3 controls the current to flow further through the voltage controlling transistor Q1, but when the base voltage of the transistor Q7 of the overcurrent limiting circuit 8 exceeds the emitter voltage set to the divided voltage Ve and further rises, the transistor Q3 Since the collector and the emitter of Q7 conduct to limit the input voltage of the driver circuit 7, the current flowing through the voltage control transistor Q1 is limited and is protected from overcurrent. When the output current further increases and the load is short-circuited, the voltage between the output terminal 2 and the ground terminal 3 decreases. In this state, since the difference between the reference voltage Vr and the divided voltage Ve is large in the differential amplifier 5, the differential amplifier 5 outputs a large difference voltage that causes a larger current to flow through the voltage control transistor Q1. The base voltage of the transistors Q2 and Q3 is sequentially increased, a large current flows through the base of the voltage control transistor Q1, and a large current is supplied to the short-circuited load. When the load is short-circuited and the output terminal voltage drops, the emitter voltage (divided voltage Ve) of the transistor Q7 drops and the base voltage rises at the same time, so that the collector and the emitter conduct, so that the input between the driver circuit 7 and the ground is connected. Short circuit. Therefore, the base current Ib of the voltage control transistor Q1 is limited, and the output current (short-circuit current) is limited.
[0006]
Thus, the stabilized DC power supply circuits disclosed in the prior arts 1 and 2 are protected from overcurrent including a load short-circuit state.
[0007]
[Problems to be solved by the invention]
By the way, the circuits shown in FIGS. 2 and 4 detect the magnitude of the base current of the voltage control transistor to protect from overcurrent and short-circuit. However, if the hfe of the voltage control transistor varies, the same applies. The output current also has a different base current value, and there is a problem in that the operating point of overcurrent limitation and short-circuit protection is influenced by hfe of the voltage control transistor.
[0008]
Therefore, it is particularly necessary to control and manufacture the hfe of the voltage control transistor, and it is necessary to adjust the value of the resistor connected to the base of the voltage control transistor according to the value of hfe. Was.
[0009]
Further, since the overcurrent detection section of the overcurrent limiting circuit is incorporated in the drive circuit of the voltage control transistor, it is necessary to suppress variations in the transistors of the drive circuit.
[0010]
[Means for Solving the Problems]
The present invention has been proposed for the purpose of solving the above-mentioned problem, and a resistor for current detection and a main current path of a transistor for voltage control are connected in series between an input terminal and an output terminal, so that an output terminal and a ground terminal are connected. And a reference voltage and a voltage divided by the voltage detecting resistor are input to a differential amplifier to amplify a difference voltage between the voltages, and the amplified voltage difference is used to control the voltage. Controls the conduction of the output transistor and outputs a stabilized DC voltage to the output terminal, detects the voltage drop of the current detection resistor, and detects the voltage drop between the output of the differential amplifier and the voltage detection resistor. [0011] A DC stabilized power supply circuit is provided, comprising an overcurrent limiting circuit for controlling conduction and limiting a current flowing through the voltage control transistor.
BEST MODE FOR CARRYING OUT THE INVENTION
A DC stabilized power supply circuit according to the present invention detects a voltage drop of a current detection resistor inserted between an input terminal and a voltage control transistor, and detects a voltage drop in proportion to a reference voltage and an output terminal voltage by the detected voltage. And an overcurrent limiting circuit that controls conduction between the output of the differential amplifier that amplifies the voltage difference between the differential amplifier and the connection of the voltage detection resistor to limit the current flowing through the voltage control transistor. However, this overcurrent limiting circuit has a first circuit in which an emitter is connected between a current detecting resistor and a voltage controlling transistor, a base and a collector are short-circuited, and a collector is grounded via a constant current source circuit. A current consisting of a transistor and a second transistor whose base is commonly connected to the base of the first transistor, whose emitter is connected to the input terminal, and whose collector is grounded via a resistor And a circuit including a third transistor whose base is connected to the collector of the second transistor, the collector is connected to the output of the differential amplifier, and the emitter is connected between the voltage detecting voltage dividing resistors. be able to.
[0012]
【Example】
An embodiment of the present invention will be described below with reference to FIG. In the figure, 11 is an input terminal to which an unstabilized DC voltage (input voltage) Vi is supplied, 12 is an output terminal to which a stabilized output voltage Vo is output, 13 is a ground terminal, R11 is a current detecting resistor, Q11 is a PNP-type voltage controlling transistor, R12 and R13 are voltage detecting resistors (voltage detecting voltage dividing resistors) connected in series and detecting a voltage at an intermediate connection point, between the input terminal 11 and the output terminal 12. The current detection resistor R11 and the main current path from the emitter to the collector of the voltage control transistor Q11 are connected in series, and the resistors R12 and R13 are connected in series between the output terminal 12 and the ground terminal 13. Reference numeral 14 denotes a reference voltage generation circuit for generating a reference voltage Vr, and reference numeral 15 denotes a voltage Ve divided by the voltage detection resistors R12 and R13 and the reference voltage Vr of the reference voltage generation circuit 4, and amplifies a difference voltage therebetween. The differential amplifier 16 is inserted between the output of the differential amplifier 15 and the base of the voltage control transistor Q11 so that the differential voltage between the divided voltage Ve, which is the input voltage of the differential amplifier 15, and the reference voltage Vr is constant. The conduction control of the voltage control transistor Q11 is performed, and the stabilized output voltage Vo is output to the output terminal 2. Reference numeral 17 denotes a safe operation area limiting circuit for limiting the voltage control transistor Q11 so as to operate within the safe operation area, and includes a resistor R14, an overvoltage detecting zener diode D1 arranged in a reverse direction, a resistor R15, and a forward arranged overvoltage. The detection diode D2 is connected in series between the emitter and the collector of the voltage control transistor Q11. The overvoltage applied to both ends of the transistor Q11 is absorbed and protected by the diodes D1 and D2. An overcurrent limiting circuit 18 connects the bases of a pair of transistors (first and second transistors) Q12 and Q13 in common, directly connects the base and collector of one transistor Q12, and connects the emitter of the transistor R12 to the resistor R14. , The collector of the transistor Q12 is grounded via the current source 19, and the emitter of the other transistor Q13 is connected to the input terminal 11 via the resistor R16. The collector of the first and second transistors Q12 and Q13 constituting the current mirror circuit is connected to the collector of the other transistor Q13 by connecting the base of the transistor (third transistor) Q14 to the collector via the resistor R17. The collector of the transistor Q14 is connected to the output terminal of the differential amplifier 5, and the emitter is connected to a voltage detecting resistor. It is connected to the connection point of R12, R13. In the illustrated example, the first and second transistors Q12 and Q13 are of PNP type, and the third transistor Q14 is of NPN type.
[0013]
The operation of the stabilized DC power supply circuit will be described. When the input voltage Vi is supplied to the input terminal 11, a reference voltage Vr is generated at the output of the reference voltage generation circuit 14. On the other hand, a voltage, which is obtained by subtracting the voltage between the emitter and the collector of the voltage control transistor Q11 from the voltage of the input terminal 11, is generated at the output terminal 12, and is connected to the connection point of the voltage detection resistors R12 and R13 according to this voltage. A voltage Ve is generated. The reference voltage Vr and the divided voltage Ve are respectively input to the differential amplifier 15, and the amplified difference voltage between the voltages Vr and Ve is connected to the base of the voltage control transistor Q11 via the drive circuit 16. Therefore, the voltage between the emitter and the collector of the voltage control transistor Q11 changes according to the difference voltage between the voltages Vr and Ve, and the output voltage of the output terminal 12 outputs a constant voltage Vo and the input voltage Vi supplied to the input terminal 11 Is stabilized, the output terminal 12 outputs the stabilized output voltage Vo.
[0014]
Next, the operation of the protection circuit of the DC stabilized power supply circuit will be described. When a large amplitude ripple or line noise is superimposed on the input voltage Vi supplied to the input terminal 11 and an excessive voltage exceeding the safe operation area of the voltage control transistor Q11 is supplied and exceeds the reverse voltage of the diode D1, A current flows through the resistors R14 and R15. Therefore, the voltage applied between the emitter and the collector of the voltage control transistor Q11 is limited to a voltage obtained by adding the reverse voltage of the diode D1, the forward voltage of the diode D2, and the voltage between the terminals of the resistors R14 and R15. Q11 is protected. In the pair of transistors Q12 and Q13 forming the current mirror circuit, when the current flowing through the transistor Q12 increases or decreases, the collector current of the transistor Q13 also increases or decreases. Since the emitter of the transistor Q12 is connected to the connection point between the current detection resistor R11 and the emitter of the voltage control transistor Q11 via the resistor R14, when a current flows through the current detection resistor R11, the voltage between the terminals of the resistor R11 becomes As a result, the emitter voltage of the transistor Q12 decreases. As a result, the emitter current of the transistor Q12 increases, and the collector current of the transistor Q13 also increases, so that the collector voltage grounded via the resistor R17 increases. That is, the collector voltage of the transistor Q13 fluctuates according to the current flowing through the current detection resistor R11, and if the current flowing through the resistor R11 increases, the collector voltage of the transistor Q13 increases. When the collector voltage of the transistor Q13 rises in this manner, the voltage between the base and the emitter of the transistor Q14 rises. Therefore, when the current flowing through the current detecting resistor R11, that is, the output current flowing from the output terminal 12 to the load increases, the transistor Q14 becomes The state changes from the non-conducting state to the conducting state, the conduction between the output of the differential amplifier 15 and the ground is performed, the output of the differential amplifier 15 is reduced, the base voltage of the voltage control transistor Q11 is increased through the drive circuit 16, and the voltage control is performed. The voltage between the emitter and the collector of the transistor Q11 is increased, the output voltage Vo is reduced, and the current is limited. Further, when the voltage at the output terminal 12 drops to almost the ground voltage, such as when the load connected between the output terminal 12 and the ground terminal 13 is short-circuited, the divided voltage Ve at the connection point becomes almost the ground voltage, and the differential amplifier 15 An attempt is made to control the voltage control transistor Q11 so as to output a difference voltage from the reference voltage Vr and raise the voltage at the output terminal 12. However, when the load is short-circuited, a large current flows through the current detection resistor R11. , The collector current of the transistor Q13 increases, the transistor Q14 is turned on, the output of the differential amplifier 15 is grounded, the base voltage of the voltage control transistor Q11 is raised, and the voltage of the voltage control transistor Q11 is reduced. Raises the voltage between the emitter and collector, reduces the output voltage Vo and limits the current .
[0015]
As described above, this DC stabilized power supply circuit keeps the output voltage constant from the state where the output current is almost zero with no load connected to the output terminal 2 to a predetermined current, and controls the voltage when the output current exceeds the predetermined current. Since the emitter and collector voltages of the transistor Q11 rise and the collector current is limited, the output voltage decreases and the output current decreases, so that the output current decreases. You. In this DC stabilized power supply circuit, the transistor Q14 for restricting the operation of the voltage control transistor Q11 is independent of the voltage control transistor Q11 and its drive circuit 16, and the voltage supplied to the base of the transistor Q14 is Rather than being set by the base current of the voltage control transistor Q11, the main current flowing through the voltage control transistor Q11 is directly detected by the current detection resistor R11 and amplified and supplied by the current mirror circuit. The voltage supplied to the base of Q14 is not affected by the hfe of the voltage control transistor Q11, and the divided voltage of the voltage detection resistor is supplied to the emitter. The voltage of the output terminal 12 is close to the ground voltage in the reduced state and the load short-circuit state In this state, the voltage between the base and the emitter of the transistor Q14 can be increased as compared with the prior arts 1 and 2, especially when the load is short-circuited. The conduction of the voltage control transistor Q11 can be reliably controlled even with the current, the internal power consumption when the protection circuit is in operation can be reduced, and the fold-back characteristics can be improved.
[0016]
【The invention's effect】
As described above, the stabilized DC power supply circuit according to the present invention is not affected by the variation in hfe of the voltage control transistor, can reliably limit the overcurrent including the load short-circuit state, suppress the short-circuit current, and reduce the internal power consumption. Thus, a stabilized DC power supply circuit having good square-shaped characteristics can be realized.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a stabilized DC power supply circuit according to the present invention. FIG. 2 is a circuit diagram showing an example of a stabilized DC power supply circuit with an overcurrent limiting circuit. FIG. 3 is an output voltage-output of the circuit shown in FIG. FIG. 4 is a circuit diagram showing another example of a stabilized DC power supply circuit with an overcurrent limiting circuit.
DESCRIPTION OF SYMBOLS 11 Input terminal 12 Output terminal 13 Ground terminal 14 Reference voltage generating circuit 15 Differential amplifier 16 Drive circuit 18 Overcurrent limiting circuit Q11 Voltage controlling transistor Q14 Transistor R11 Current detecting resistors R12, R13 Voltage detecting dividing resistor Ve Voltage division Voltage Vi Input voltage Vo Output voltage Vr Reference voltage

Claims (2)

The current detection resistor and the main current path of the voltage control transistor are connected in series between the input terminal and the output terminal, the voltage detection resistor is connected between the output terminal and the ground terminal, and the voltage is divided by the voltage detection resistor. The amplified voltage and the reference voltage are input to a differential amplifier to amplify a difference voltage between the voltages, and the DC voltage stabilized at an output terminal by controlling conduction of the voltage control transistor by the amplified difference voltage. And an overcurrent limiting circuit that controls conduction between the output of the differential amplifier and the voltage dividing resistor for voltage detection based on the current flowing through the current detecting resistor to limit the current flowing to the voltage controlling transistor. A stabilized DC power supply circuit comprising: The overcurrent limiting circuit includes a first transistor having an emitter connected between a current detecting resistor and a voltage controlling transistor, a short circuit between a base and a collector, a collector grounded via a constant current source circuit, and a base. Are commonly connected to the base of the first transistor, the current mirror circuit includes a second transistor having an emitter connected to the input terminal, and a collector grounded via a resistor, and a base connected to the collector of the second transistor. 2. The stabilized DC power supply circuit according to claim 1, further comprising a third transistor connected to the output of the differential amplifier and connected to the output terminal of the differential amplifier.

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