JP2002049430A - Power source circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power source circuit capable of reducing the current capabilities of an input side DC power source, and preventing the generation of any failure such as hit due to rush currents. SOLUTION: A DC power source is supplied from an output terminal (16) through an output transistor (Q1) to a load, and the driving of the output transistor (Q1) is controlled so that the voltage of the output terminal (16) can be made constant according to an error voltage obtained by comparing the voltage of the output terminal (16) with a reference voltage. This power source circuit is provided with a current detecting circuit (Q2) for detecting currents flowing through the output transistor (Q1) and a soft start circuit (20) for suppressing the driving of the output transistor (Q1) according to the currents detected by the current detecting circuit (Q2) at the time of start. Thus, it is possible to suppress rush currents at the time of start, and to prevent the generation of hit due to the rush currents even when the current capabilities of the input side DC power source are small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power supply circuit, and more particularly, to a power supply circuit for stabilizing and outputting a DC power supply.

[0002]

2. Description of the Related Art Conventionally, there is a power supply circuit for stabilizing and outputting a DC power supply. FIG. 5 shows a circuit configuration diagram of an example of a conventional power supply circuit. This power supply circuit is integrated in a semiconductor.

In FIG. 1, a positive electrode of a DC power supply 10 is connected to an external input terminal 12, and a negative electrode of the DC power supply 10 is grounded. The external input terminal 12 is connected to the emitter of the output pnp transistor Q1. The base of the output transistor Q1 is connected to the output terminal of the error amplifier 14 and is supplied with an error voltage.
One collector is connected to the external output terminal 16.

One end of a load resistor Ro is externally connected to the external output terminal 16, and one end of a phase compensation capacitor Co for preventing oscillation of the error amplifier 14 is externally connected.
The other ends of the load resistance Ro and the capacitor Co are grounded.

The external output terminal 16 is grounded via resistors R1 and R2 connected in series.
The connection point 2 is connected to the non-inverting input terminal of the error amplifier 14. The reference voltage Vref is supplied from the voltage source 18 to the inverting input terminal of the error amplifier 14. The error amplifier 14 differentially amplifies the output voltage Vo divided by the resistors R1 and R2 and the reference voltage Vref. Generate an error voltage. This error voltage is supplied to the base of the output transistor Q1, and the drive of the output transistor Q1 is controlled so that the output voltage Vo becomes constant.

[0006]

Problems to be Solved by the Invention FIGS. 6A and 6B
2 shows a waveform diagram of the input voltage Vin, the output voltage Vo, and the output current Io when the conventional power supply circuit is started.

In the above-described conventional power supply circuit, a rush current Irush is generated at the time of startup. Rush current Irush
Is the charging current of the capacitor Co externally connected to the external output terminal 16 of the power supply circuit, and is the upper limit of the output current of the power supply circuit.

In the conventional power supply circuit, the DC power supply 10 on the input side is required to have a current capability higher than the rush current in order to avoid the instantaneous interruption caused by the generation of the rush current. There was a problem that also becomes high.

The present invention has been made in view of the above points, and provides a power supply circuit capable of reducing the current capability of a DC power supply on the input side and preventing occurrence of a short-circuit failure due to a rush current. The purpose is to do.

[0010]

According to a first aspect of the present invention, an output terminal (1) is connected through an output transistor (Q1).
6) DC power is supplied to the load from the output terminal (1).
6) A power supply circuit for driving and controlling the output transistor (Q1) so that the voltage at the output terminal (16) becomes constant according to an error voltage obtained by comparing the voltage of the output transistor (Q1) with the reference voltage. ), And a soft start circuit (2) which suppresses the driving of the output transistor (Q1) at the time of start-up according to the current detected by the current detection circuit (Q2).
0).

As described above, at the time of start-up, the output transistor (Q1) is changed according to the current flowing through the output transistor (Q1).
By suppressing the driving of 1), the rush current at the time of starting can be suppressed, and even if the current capability of the DC power supply on the input side is small, occurrence of instantaneous interruption due to the rush current can be prevented.

According to a second aspect of the present invention, in the power supply circuit according to the first aspect, the soft start circuit (20) is provided.
Has a capacitor (Css) that is charged at startup,
The driving of the output transistor (Q1) is suppressed only for the time until the capacitor (Css) is charged.

As described above, since the driving of the output transistor (Q1) is suppressed only for the time until the capacitor (Css) is charged, the soft start circuit (2
0) can be activated and not activated in the steady state.

According to a third aspect of the present invention, in the power supply circuit according to the second aspect, the soft start circuit (20) is provided.
Is a transistor (Q5) that turns on when the output terminal (16) is short-circuited and discharges the capacitor (Css).
Having.

As described above, when the output terminal (16) is short-circuited, the transistor (Q5) is turned on to turn on the capacitor (Cs).
s), the soft start circuit (20) can be operated again when returning from the short circuit.

The invention described in claim 4 is the first to third aspects of the present invention.
In the power supply circuit according to any one of the above,
6) a current limit circuit (22) for suppressing the driving of the output transistor (Q1) in accordance with the current detected by the current detection circuit (Q2) when the short circuit occurs.

As described above, when the output terminal (16) is short-circuited, the driving of the output transistor (Q1) is suppressed according to the current detected by the current detection circuit (Q2). Can be suppressed.

The reference numerals in the parentheses are provided for easy understanding, are merely examples, and are not limited to the illustrated embodiment.

[0019]

FIG. 1 is a block diagram showing an embodiment of a power supply circuit according to the present invention, and FIG. 2 is a circuit diagram thereof. This power supply circuit is integrated in a semiconductor, and the same parts as those in FIG. 4 are denoted by the same reference numerals.

1 and 2, the positive electrode of the DC power supply 10 is connected to the external input terminal 12, and the negative electrode of the DC power supply 10 is grounded. The external input terminal 12 has an output pn
The emitter of the p transistor Q1 and the emitter of the current detection pnp transistor Q2 (current detection circuit) are connected. The emitter areas of the transistors Q1 and Q2 have a relationship of n: 1 (n is a positive real number).
The bases of the transistors Q1 and Q2 are npn for driving.
It is connected to the collector of transistor Q3. The collector of the transistor Q1 is connected to the external output terminal 16, the resistor R10 of the soft start circuit 20 and the transistor Q5, and the resistor R1 of the current limit circuit 22.
2 are connected.

The emitter of the transistor Q3 is grounded,
The base is connected to the output terminal of the error amplifier 14 and the transistor Q7 of the soft start circuit 20, and is supplied with an error voltage.

One end of a load resistor Ro is externally connected to the external output terminal 16, and one end of a phase compensation capacitor Co for preventing oscillation of the error amplifier 14 is externally connected.
The other ends of the load resistance Ro and the capacitor Co are grounded.

The external output terminal 16 is grounded via resistors R1 and R2 connected in series.
2 is connected to the amplifier section 14 that constitutes the error amplifier 14.
a is connected to the non-inverting input terminal. Error amplifier 1
Reference numeral 4 denotes an amplifier 14a shown in FIG. 2 and a driving transistor Q3, and a reference voltage Vref is supplied from a voltage source 18 to an inverting input terminal of the amplifier 14a. The amplifier 14a differentially amplifies a voltage obtained by dividing the output voltage Vo by the resistors R1 and R2 and a reference voltage Vref to generate an error voltage. This error voltage is supplied to the base of the driving transistor Q3, the collector current of the transistor Q3 is supplied to the bases of the output transistor Q1 and the current detection transistor Q2, and the error amplifier 14 controls the output voltage Vo to be constant. The drive control of the output transistor Q1 is performed. Further, the current detection transistor Q2 detects the collector current of the output transistor Q1, and passes 1 / n of the collector current.

The soft start circuit 20 includes a resistor R10,
R11, transistors Q4 to Q7, and an external capacitor Css. Resistor R1 connected in series
0 and R11 are connected between the collector of the transistor Q1 and the ground. The connection point of the resistors R10 and R11 is pnp
Base of transistor Q4 and pnp transistor Q5
And one end of a capacitor Css is connected via an external terminal 24. The other end of the capacitor Css is grounded.

The transistor Q4 has an emitter connected to the collector of the transistor Q2, and a collector connected to the collector and the base of the npn transistor Q6. The transistor Q5 has a base connected to the collector of the transistor Q1, and a collector grounded.

The base of transistor Q6 is commonly connected to the base of npn transistor Q7. The emitters of the transistors Q6 and Q7 are grounded to form a current mirror circuit, and the collector of the transistor Q7 is connected to the base of the transistor Q3.

The current limit circuit 22 includes a resistor R1
2, R13 and transistors Q8 to Q10. The resistors R12 and R13 connected in series are connected between the collector of the transistor Q1 and the ground. Resistance R1
The connection point of R2 and R13 is connected to the base of pnp transistor Q8. Transistor Q8 has an emitter connected to the collector of transistor Q2, and a collector connected to np
It is connected to the collector and base of n-transistor Q9.

The resistance values of the resistors R10 to R13 are, for example, R10 = R12, R11> R13.
The potential at the connection point of the resistors R10 and R11 is equal to the resistance of the resistors R12 and R1.
3 is set higher than the potential of the connection point.

The base of transistor Q9 is commonly connected to the base of npn transistor Q10. The emitters of the transistors Q9 and Q10 are grounded to form a current mirror circuit, and the collector of the transistor Q10 is connected to the base of the transistor Q3.

Here, when the power supply circuit is started, the capacitor Css is discharged and the voltage Vss of the external terminal 24 becomes 0V.
Therefore, the transistor Q of the soft start circuit 20
4 turns on. Therefore, 1 / n of the rush current Irush flowing from the transistor Q1 to the capacitor Co through the external output terminal 16 becomes the collector current of the transistor Q2, and this current is the current of the transistors Q4 and Q6.
And the same amount of collector current as the collector current of the transistor Q6 flows to the transistor Q7 forming a current mirror. For this reason, the base potential of the transistor Q3 decreases, and the collector current of the transistor Q3 decreases, thereby suppressing the rush current Irush.

Since the suppression period of the rush current Irush is determined by the time constant of the resistor R10 and the capacitor Css, by appropriately selecting the capacitance of the capacitor Css in accordance with the output voltage Vo, the rush current Irush is constantly applied to the load resistor Ro. Can be set so as not to exceed the load current Io flowing through 3A and 3B show the input voltage V of the external input terminal 12 when the power supply circuit is started.
in, the voltage Vss of the external terminal 24, and the external output terminal 1
6 shows a waveform diagram of the output voltage Vo and a waveform diagram of the output current Io of the external output terminal 16.

In the steady state, since the capacitor Css is charged, the transistor Q4 is turned off, and the soft start circuit 20 stops operating. From this state, FIG.
As shown in (A), for example, when the external output terminal 16 is short-circuited to the ground level, the potential at the connection point between the resistors R10 and R11 is set to be higher than the potential at the connection point between the resistors R12 and R13. Therefore, the transistor Q8 of the current limit circuit 22 turns on.

When the transistor Q8 is turned on, 1 / n of the collector current of the transistor Q1 becomes the collector current of the transistor Q2. This current flows through the paths of the transistors Q8 and Q9 and has the same amount of collector current as the collector current of the transistor Q9. A current flows through transistor Q10 forming a current mirror. Therefore, the base potential of the transistor Q3 is reduced, and the collector current of the transistor Q3 is reduced. As a result, the collector current of the transistor Q1 is limited to the current Icl as shown in FIG.

Further, since the potential of the external output terminal 16 decreases, the transistor Q5 of the soft start circuit 20 turns on, and the capacitor Css is discharged. by this,
The quick start of the soft start circuit 20 when returning from the short circuit of the external output terminal 16 is enabled.

As described above, by providing the soft start circuit 20, even if the current capability of the DC power supply 10 on the input side is small, it is possible to prevent an instantaneous interruption due to a rush current, and the DC power supply on the input side can be prevented. The current capacity can be reduced, and the cost of the DC power supply can be reduced.

[0036]

As described above, the first aspect of the present invention provides
By suppressing the driving of the output transistor according to the current flowing through the output transistor at the time of startup, the rush current at the time of startup can be reduced. Disconnection can be prevented, the current capability of the input-side DC power supply can be reduced, and the cost of the DC power supply can be reduced.

According to the second aspect of the present invention, the driving of the output transistor is suppressed only for the time until the capacitor is charged.
Steady state can be disabled.

According to the third aspect of the present invention, when the output terminal is short-circuited, the capacitor is discharged by turning on the output terminal. Therefore, when the short-circuit is restored, the soft-start circuit can be operated again.

According to a fourth aspect of the present invention, when the output terminal is short-circuited, the driving of the output transistor is suppressed in accordance with the current detected by the current detection circuit. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram of a power supply circuit according to an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of an embodiment of a power supply circuit of the present invention.

FIG. 3 is a waveform diagram of an input voltage Vin, a voltage Vss, an output voltage Vo, and an output current Io when the power supply circuit is started.

FIG. 4 is a waveform chart for explaining the operation of the current limit circuit.

FIG. 5 is a circuit configuration diagram of an example of a conventional power supply circuit.

FIG. 6 shows an input voltage Vi when a conventional power supply circuit is started.
FIG. 4 is a waveform diagram of n, output voltage Vo, and output current Io.

[Explanation of symbols]

 Reference Signs List 10 DC power supply 12 External input terminal 14 Error amplifier 14a Amplifier 16 External output terminal 18 Voltage source 20 Soft start circuit 22 Current limit circuit 24 External terminal Co capacitor Q1 Output transistor Q2 Current detection transistor Q3 to Q10 Transistor Ro Load resistance R1 to R13 resistance

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/822

Claims (4)

[Claims] 1. A DC power source is supplied from an output terminal to a load through an output transistor, and the output terminal voltage becomes constant according to an error voltage obtained by comparing the output terminal voltage with a reference voltage. A power supply circuit for controlling the driving of the transistor, comprising: a current detection circuit for detecting a current flowing through the output transistor; and a soft start circuit for suppressing the driving of the output transistor according to the current detected by the current detection circuit at startup. A power supply circuit, characterized in that: 2. The power supply circuit according to claim 1, wherein the soft start circuit has a capacitor that is charged at the time of starting, and suppresses driving of the output transistor for a time until the capacitor is charged. Characteristic power supply circuit. 3. The power supply circuit according to claim 2, wherein the soft start circuit includes a transistor that is turned on when the output terminal is short-circuited and discharges the capacitor. 4. The power supply circuit according to claim 1, wherein when the output terminal is short-circuited, a current limit circuit that suppresses driving of the output transistor according to a current detected by the current detection circuit. A power supply circuit comprising: