JPH117329A - Stabilizing power circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of rejection function as against a ripple while suppressing an operation voltage at a regulation control side by grounding the base of a succeeding stage in Darlington connection in accordance with an output voltage reduction detecting signal. SOLUTION: A current booster circuit 3 is provided with a switch circuit 2 between the base and the ground GND of a past stage transistor Q8. The switch circuit 2 is turned-on by the detecting signal of an output voltage detecting circuit 4. The succeeding stage transistor Q8 of Darlington connection is turned off by turning-on the circuit 2 and the drive stage 1 of the current booster circuit 3 becomes an emitter grounded circuit consisting of a preceding stage transistor Q7. Besides, the amplifying rate of the drive stage 1 of the current booster circuit 3 is preserved in a large state so that a large difference from the operation state of Darlington connection in the amplifying rate is eliminated. In a result, the temporary deterioration of the injection function as against the ripple by a change point where the amplifying rate changes is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stabilized power supply circuit, and more particularly to a stabilized power supply circuit without increasing an operation voltage on a regulation control side, not deteriorating a rejection function for ripples, and preventing a start-up failure from occurring. The present invention relates to a stabilized power supply circuit integrated into an IC.

[0002]

2. Description of the Related Art As a conventional stabilized power supply circuit integrated into an IC, a differential amplifier circuit 10 (or an operational amplifier, where the operational amplifier is included in the differential amplifier circuit) as shown in FIG. It will be explained.) And the current booster circuit 11
And a device utilizing a constant current circuit comprising: In this circuit, 12 is an output terminal for generating a constant voltage, and 13 is a power supply for generating a reference voltage V1 applied to one input of the differential amplifier circuit. The differential amplifier circuit 10 includes a differential amplifier 10a and a constant current source 10b (its current value I) of the differential amplifier 10a, and includes a series connection of resistors R1 and R2 as a load of the current booster circuit 11. Circuit is inserted. Here, the PNP transistors Q1 and Q2 each have a constant current circuit 1 connected to the emitter side.
0c and 10d are driving transistors. The reference voltage V1 is applied to the base of the transistor Q1. The current booster circuit 11 is connected to the base of the transistor Q2.
Receives the voltage that is fed back from the output side. The PNP transistors Q3 and Q4 are a pair of transistors constituting a differential amplifier 10a in which the bases are coupled to the emitters of the transistors Q1 and Q2.

The transistor Q5 is a current booster circuit 1
1 is an NPN transistor of the drive stage, and its base is the transistor Q4 of the amplification stage of the differential amplifier circuit 10.
Is driven by receiving its output from its collector at its base. And, through the collector, the PNP of the current output stage
Drives the base of transistor Q6. The collector of the transistor Q6 is connected to the output terminal 12, and is grounded via the resistors R1 and R2. The terminal voltage of the resistor R2 (the voltage at the connection point N of these resistors) is
0 is fed back to the base of the transistor Q2, whereby the differential amplifier circuit 10 operates so that the terminal voltage generated at the resistor R2 matches the reference voltage V1, and the constant voltage V1 is generated at the output terminal 12. This constant voltage Vo is as follows: Vo = (r1 + r2) .V1 / r2. Here, r1 is the resistance value of the resistor R1, and r2 is the resistor R2.
Is the resistance value. The power supply voltage of the differential amplifier circuit 10 is connected to the stabilized power supply line Vreg, and the power supply voltage of the current booster circuit 11 is equal to the normal power supply line + Vcc.
It is connected to the.

[0004]

In such a stabilized power supply circuit, when the load side is short-circuited, the output terminal 1
2 drops to the ground potential, the input (base of the transistor Q2) of the differential amplifier circuit 10 whose output is fed back drops to the ground potential, and the transistor Q4 of the differential amplifier circuit 10 driving the current booster circuit 11 becomes The transistor Q3 is turned "ON" and the other transistor Q3 is turned "OFF". Therefore, the current for driving the current booster circuit 11 becomes the current I supplied from the current source 10b, and when the load side is short-circuited, a large current flows to the full capacity of each element and I
There is a problem that C is heated and ICs including peripheral circuits are destroyed. In this case, the current booster circuit 11
Assuming that the output current is Io, Iooβp · βn · I. Here, βp is the current gain of the output transistor Q6 of the current booster circuit 11, and βn is the current gain of the transistor Q5 in the drive stage of the current booster circuit.

Therefore, in order to solve such a problem, the NPN transistor Q5, which is the drive stage of the current booster circuit 11, is replaced with two NPN transistors, and the NPN transistor Q5 of the preceding transistor which drives the base of the subsequent transistor is used. A circuit in which a bias resistor is inserted between an emitter and a ground GND to form an emitter follower and a subsequent stage is provided with a drive stage having a grounded emitter is disclosed in Japanese Patent Laid-Open No. 2-133.
No. 810 "Stable power supply circuit". However, in the drive stage of this current booster circuit, the bias resistance is connected to the base of the transistor in the subsequent stage and the ground GND.
Since it is also inserted between D, when the output current is small and the load is low, only the pre-stage transistor operates.
The transistor in the preceding stage has a low amplification factor when operated alone since a resistor is inserted in the emitter. Therefore, there is a large difference between the amplification factor of the drive stage at the time of high load, in which the transistors at the front and rear stages operate, and the amplification factor of only the transistor at the front stage at the time of low loads, and the change point where the amplification ratio changes is Occur. As a result, it has been found that the point of change acts when the state of the load changes abruptly, and this stabilized power supply circuit has a problem of temporarily deteriorating the function of rejecting (rejecting) ripples.

In order to avoid such a situation, it has been considered that the bias resistor is removed to completely connect the transistor of the drive stage of the current booster circuit to the Darlington connection. Since the bias voltage becomes 2 Vf and the bias voltage of the differential amplifier circuit 10 on the regulation control side is increased by 1 Vf (forward voltage drop between base and emitter), the bias voltage of the entire circuit also needs to be increased by 1 Vf. . As a result, the control voltage for regulation must be set higher by 1 Vf, and there is a problem that the operating range of the stabilized power supply circuit is reduced. further,
When the drive stage of the current booster circuit is completely Darlington-connected, the base potential of the transistor Q2 becomes the ground potential at the time of startup, so that the transistor Q4 saturates, the base bias voltage of the drive stage falls below 2Vf, Current cannot be supplied, and there is a problem that start-up failure occurs. SUMMARY OF THE INVENTION An object of the present invention is to solve such problems of the prior art, without increasing the operation voltage on the regulation control side, without deteriorating the rejection function for ripples, and further, when starting failure occurs. To provide a stabilized power supply circuit.

[0007]

To achieve the above object, a stabilized power supply circuit according to the present invention has a differential amplifier circuit and a current amplifier circuit which receives an output from the differential amplifier circuit and amplifies the current. Then, a voltage divider of a series resistor is inserted in parallel with an output to which the load of the current amplifier is connected, the divided voltage is fed back to one input of the differential amplifier, and a constant voltage is applied to the other input. In addition, in a constant current drive type stabilized power supply circuit that supplies regulated output voltage power to the load by passing a constant current through the voltage divider circuit, the Darlington connection of the current amplifier circuit receives the output of the differential amplifier circuit. A transistor having an input stage and a current output stage driven by the Darlington-connected transistor, wherein any one of an output voltage, the divided voltage and voltages corresponding to these voltages is a predetermined reference voltage; And a switch circuit that receives the detection signal of the detection circuit and grounds the base of the transistor at the subsequent stage of the Darlington connection to operate only the transistor at the previous stage. is there.

[0008]

According to such a configuration, when a large current flows through the load and the output voltage drops, the base of the subsequent stage of the Darlington connection is grounded in accordance with the detection signal, so that the preceding transistor is It becomes a common emitter circuit that does not pass a resistor to the emitter. At this time, the gain of the drive stage of the current booster circuit is maintained at a large state, so that there is no large difference in the gain between the Darlington connection and the operating state. As a result, temporary deterioration of the rejection function for ripples due to a change point where the amplification factor changes is suppressed. Moreover, when the output voltage drops, the drive stage of the current booster circuit becomes a common emitter circuit, so that the operation can be performed without increasing the bias voltage of the differential amplifier circuit on the regulation control side by 1 Vf. On the other hand, at the time of start-up, the drive stage of the current booster circuit is similarly a grounded emitter circuit of one transistor, so that the base potential can be operated from 1 Vf. Therefore, no startup failure occurs. In the embodiment, when the output voltage at the time of short-circuit decreases to the ground level, a short-circuit detection circuit is separately provided so that the operation of the detection circuit does not operate at the time of short-circuit. This distinguishes between a start-up and a short-circuit that occurs during a steady operation.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram of a stabilized power supply circuit to which the present invention is applied, FIG. 2 is a block diagram of an embodiment using a comparator in the output voltage detection circuit of FIG. 1, and FIG. 3 is an output voltage detection circuit of FIG. FIG. 2 is a block diagram of an embodiment using a current switching circuit as an example. Note that the same components as those in FIG. 4 are denoted by the same reference numerals. The current booster circuit 3 of FIG.
Is a Darlington-connected drive stage 1 composed of transistors Q7 and Q8 in place of the transistor Q5 in the drive stage of the current booster circuit 11 in FIG. Further, the base of the transistor Q8 at the subsequent stage is connected to the ground GND.
The switch circuit 2 is provided between the two. The switch circuit 2 is turned on by the detection signal of the output voltage detection circuit 4.
To be. By this ON, the transistor Q8 at the subsequent stage of the Darlington connection is turned OFF, and the drive stage 1 of the current booster circuit 3 at this time,
It becomes a common emitter circuit consisting of seven. That is, when the output voltage is equal to or lower than a predetermined value, or at the time of startup at the ground level (excluding the short-circuit state, which will be described later), the circuit becomes the same as the circuit of FIG. 4 described above.

The output voltage detecting circuit 4 includes a differential amplifying circuit 10
, And operates when it receives a detection signal from the short-circuit detection circuit 5 and does not receive this signal. This is because when the output voltage is received from the output terminal 12 and is compared with the reference voltage value Vref of the reference power supply 6, when the output voltage becomes equal to or lower than the reference voltage value Vref, a detection signal is generated and the switch is generated. Circuit 2 is turned on.
At other times, the switch circuit 2 is off. As a result, when the stabilized power supply circuit starts up and when a large current flows through the load and the output voltage becomes equal to or lower than the reference voltage value Vref, the drive stage 1 of the current booster circuit 3 is activated.
Changes from a Darlington-connected transistor circuit to a grounded-emitter circuit having no emitter in response to the detection signal of the output voltage detection circuit 4. At this time, since the amplification factor of the drive stage 1 is maintained at a large state, there is no large difference in the amplification factor from the state of the Darlington connection. As a result, temporary deterioration of rejection of ripple due to a change point where the amplification factor changes is suppressed.

The short-circuit detection circuit 5 operates by receiving power from the power supply line Vreg, receives the output voltage from the output terminal 12, and when the output voltage drops to the ground GND level or a short-circuit level close to this, the output voltage detection circuit 5 4 is stopped to prevent the generation of the detection signal. As a result, in a steady operation state in which the voltage of the power supply line Vreg is a normal voltage, if the output drops to a level such that the load is short-circuited, the drive stage 1 of the current booster circuit is set to Darlington. Return to connected state. At this time, the transistors Q7 and Q8 are operating. The power supply line Vreg is a power line supplied from a circuit whose voltage is regulated to a constant voltage. Usually, the predetermined constant voltage is obtained when the power supply voltage becomes equal to or higher than a predetermined value from the start. It is. The short-circuit detection circuit 5 operates in a range equal to or higher than the lower limit of the regulated range with reference to this constant voltage. this is,
Simply, the bias voltage for starting the operation of the transistor in this circuit may be set to a voltage equal to or higher than the above lower limit.

The operation in the short-circuit state and the operation at the time of startup will be described below. The base of the PNP transistor Q6 in the current output stage is commonly connected to the collector of the transistor Q7 and the collector of the transistor Q8. Driven in common by transistors. The resistance R3
Is a bias resistor inserted between the power supply + Vcc line and the base of the transistor Q6.
The emitter side of 6 is also connected to the power supply + Vcc line. In this circuit, when Io the output current of the current booster circuit 3, the ^{Io ≒ βp · βn 2 · I} .......... Here, βp is the PNP of the current booster circuit 3.
The current amplification factor, βn, of the output transistor Q6 of the NPN type is the NPN type transistor Q of the drive stage of the current booster circuit.
7, the current amplification factor of Q8. Here, the voltage Vo generated at the output terminal 12 of the current booster circuit 3 is as follows: Vo = (r1 + r2) · V1 / r2, but when the output terminal 12 is short-circuited, the short-circuit detection circuit 5 Operates, the switch circuit 2 is turned off.
, And the drive stage 1 becomes a Darlington connection circuit. Therefore, the drive stage 1 does not operate unless the base voltage of the transistor Q7 in the preceding stage rises above 2Vf.

That is, when a short circuit occurs, Vo = Vr2 = 0
become. Here, Vo is a voltage generated at the output terminal 12, and Vr2 is a terminal voltage of the resistor R2. At this time, the forward voltage drop between the base and emitter of the input transistor Q2 of the differential amplifier circuit 10 is Vf2, the forward voltage drop Vf4 between the base and the emitter of the amplifier transistor Q4 of the differential amplifier circuit 10, and the transistor Q4. The voltage drop due to the ON resistance between the base and collector of the current booster circuit is Vs.
The base voltage of the transistor Q7 in the previous stage of the drive stage 1 is Vf7, and Vf2 = Vf4 = V1f. However, V1f
Is a forward voltage drop between the base and the emitter of the transistor which is usually about 0.7V. Then, at this time, the potential of the collector of the transistor Q4 is equal to Vf7 and becomes 2V1f or less due to Vf7 = Vf2 + Vf4-Vs. As a result, the drive stage 1 of the current booster circuit 3 does not operate. That is, when the load is short-circuited, the current of the stabilized power supply circuit is limited.

On the other hand, when starting, the differential amplifier circuit 10
, The short-circuit detection circuit 5 does not operate. Therefore, output terminal 1
Even if the output voltage is received from 2 and the output voltage is lowered to the ground level or a short-circuit level close thereto, the detection signal of the output voltage detection circuit 4 is generated and the drive stage 1 of the current booster circuit 3 comprises the transistor Q7. Operates as a common emitter circuit. At this time, the voltage at which the operation of the drive stage 1 starts is 1 Vf, and the differential amplifier circuit 10
Current is supplied through the collector of the transistor Q4. As a result, no startup failure occurs.

FIG. 2 shows a specific example in which a comparator 40 is used in the output voltage detection circuit 4. Further, the comparator 40
The detection signal input side (+ input) of the
2, it is connected to the connection point N of the resistors R1 and R2, which are the voltage detection points of the differential amplifier circuit 10, and detects the divided voltage of the output voltage. Here, the switch circuit 2 is connected to the base of the transistor Q8 and the ground GND.
And an NPN transistor Q9 having a collector and an emitter connected between them. And the short circuit detection circuit 5
Turns off the switch circuit 41 provided between the comparator 40 and the power supply line Vreg, thereby stopping the operation of the comparator 40 and preventing generation of a detection signal.

FIG. 3 shows a circuit in which a current switching circuit 42 is used as the output voltage detecting circuit 4 in place of the comparator 40 in FIG.
The operation of the second current source 43 is stopped by interrupting the current. The current switching circuit 42 receives the current from the current source 43, and receives the current from the current source 43 via a series circuit including diode-connected PNP transistors Q10 and Q11 provided in series downstream of the current source 43 and a series-connected resistor R4. To the ground GND to generate a reference voltage Vref as the reference power supply 6. And the transistor Q1
A common emitter P with an emitter connected to the emitter of 0
An NP transistor Q12 is provided. The collector of this transistor Q12 is connected to ground GND via a resistor R5.
And the terminal voltage of the resistor R5 is applied as a detection signal to the base of the transistor Q9 (switch circuit 2) to generate a signal for turning it on. The base of the transistor Q12 is connected to a connection point N of the resistors R1 and R2 via a diode connection transistor Q13 for level shift as a detection signal input side.
It is connected to the.

As a result, when the voltage at the connection point N is lower than the voltage at the emitter of the transistor Q12 by 2 Vf or more, the transistor Q12 is turned on to generate a voltage at the resistor R1, and the current to make this voltage 1 Vf or more. Flows into the transistor Q12, the transistor Q9 is turned on. At the time of startup, as the power supply line Vcc rises and the power supply line Vcc becomes 2 Vf or more, the transistors Q10 and Q1
The operation of 1 causes the transistor Q12 to operate. At the start of this operation, the voltage at the connection point N is at the ground GND level, so that the transistor Q9 is turned on and the drive stage 1 of the current booster circuit 3 operates as a common emitter circuit. When the voltage at the connection point N reaches the ground GND level in the steady operation state, the short-circuit detection circuit 5
As a result, the current of the current source 43 is cut off, and the transistor Q9 is turned off.

As described above, in the embodiment, the short-circuit detecting circuit is provided. However, in the case where only the action of preventing the starting failure is required, or an over-current preventing circuit and a resistor are provided to prevent the short-circuit. In such a case, the above-described short-circuit detection circuit is unnecessary. Further, the output voltage detection circuit according to the embodiment can detect any one of an output voltage, a divided voltage obtained by dividing the output voltage, and a voltage corresponding to these voltages. In the embodiment, the power supply voltage is set to + Vcc and the operation is performed with the (+) power supply. However, the PNP transistor is replaced with the NPN transistor, and the NPN transistor is replaced with the PNP transistor, and the drive is performed with the (−) power supply. Of course, you can do it. Further, the number of coupling stages of the transistors in the drive stage of the current booster circuit is not limited to two, and a plurality of stages may be connected. This is the same for the configuration of the transistor of the differential amplifier circuit.

[0019]

As described above, according to the present invention, when a large current flows to the load and the output voltage drops, the base of the subsequent stage of the Darlington connection is grounded in accordance with the detection signal to reduce the output voltage. Because the drive stage of the Darlington connection current booster circuit is set to the grounded emitter circuit at the time of drop and startup, the amplification factor of the drive stage of the current booster circuit is kept large, and amplification with the state of Darlington connection No big difference in rates. Therefore, temporary deterioration of the rejection function for ripples is suppressed. On the other hand, at the time of start-up, the drive stage of the current booster circuit is similarly a grounded emitter circuit of one transistor, so that the base potential can be operated from 1 Vf. Therefore, no startup failure occurs. As a result, it is possible to realize a stabilized power supply circuit that does not increase the operation voltage on the regulation control side of the stabilized power supply circuit, does not deteriorate the rejection function for ripples, and does not cause a startup failure.

[Brief description of the drawings]

FIG. 1 is a block diagram of a stabilized power supply circuit to which the present invention is applied.

FIG. 2 is a block diagram of another embodiment using a comparator in the output voltage detection circuit of FIG. 1;

FIG. 3 is a block diagram of still another embodiment using a current switching circuit as the output voltage detection circuit of FIG. 2;

FIG. 4 is an explanatory diagram of a conventional stabilized power supply circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Drive stage of current booster circuit, 2,42 ... Switch circuit, 3,11 ... Current booster circuit, 4 ... Output voltage detection circuit, 5 ... Short circuit detection circuit, 10 ... Differential amplifier circuit, 10
a: differential amplifier, 10b: constant current source, 12: output terminal,
Reference numeral 40: comparator, 42: current switching circuit, 43: current source, R1, R2, R3: resistor, Q1 to Q13: transistor.

Claims (2)

[Claims] 1. A differential amplifier circuit and a current amplifier circuit for receiving and outputting an output of the differential amplifier circuit, and a voltage divider circuit of a series resistor is inserted in parallel with an output to which a load of the current amplifier circuit is connected. Then, the divided voltage is fed back to one input of the differential amplifier circuit, a constant voltage is applied to the other input, and a constant current flows through the voltage dividing circuit, whereby the power of the output voltage regulated to the load is obtained. Wherein the current amplifier circuit includes an input stage of a Darlington-connected transistor receiving an output of the differential amplifier circuit and a current output stage driven by the Darlington-connected transistor. A detection circuit for detecting whether any one of the output voltage, the divided voltage, and a voltage corresponding to these voltages has dropped below a predetermined reference voltage; A switch circuit that receives a signal and grounds the base of the transistor at the subsequent stage of the Darlington connection to operate only the transistor at the previous stage. 2. The stabilized power supply according to claim 1, further comprising a short-circuit detection circuit for detecting a short-circuit state of the load, and preventing generation of a detection signal of the detection circuit in accordance with a detection signal of the short-circuit detection circuit. circuit.