JP2003330550A - Constant voltage power supply circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a constant voltage power supply circuit suitable for integration and capable of reducing a bias current for a drive transistor and capacitance of a phase compensating capacitor, even when connecting a load with large fluctuation in current consumption. <P>SOLUTION: A bias circuit 5 supplying the bias current in proportion to an output current io is provided for the drive transistor P2 which drives an output transistor P1 in response to an output signal of an error amplifier circuit 4. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant voltage power supply circuit which can save power and facilitate phase compensation.

[0002]

2. Description of the Related Art FIG. 8 is a circuit diagram showing an example of a conventional constant voltage power supply circuit. In the constant voltage power supply circuit 100 of FIG. 8, an error amplification circuit 101 including a differential amplifier formed of transistors Ma to Me includes a reference voltage generation circuit 102.
The error of the divided voltage Va, which is generated by dividing the output voltage Vo by the resistors Ra and Rb with respect to the predetermined reference voltage Vr generated and output in step A, is amplified, and a signal obtained by performing the error amplification is obtained. Output to the gate of the drive transistor Mf.

The drive transistor Mf is biased by a transistor Mg whose gate is applied with a predetermined bias voltage Vb. A voltage corresponding to the current output from the drive transistor Mf is input to the gate of the output transistor Mh, and the output transistor Mh is
The output current io is controlled so that the output voltage Vo becomes constant even if the load 110 changes. In the case of FIG. 8, the output current i
As o increases, it is necessary to increase the bias current for the drive transistor Mf. Conventionally, the bias current has been set to a value corresponding to the maximum output current of the output transistor Mh.

[0004]

However, such a maximum output current is not normally output from the output transistor Mh, and in many cases, it is a fraction of the maximum output current.
It only outputs the current of. In particular, in recent devices, in order to save power, the circuits in the device are subdivided by function, and power is supplied only to circuits with required functions when needed. Has started to change significantly.

When the output current io is small, the bias current to the drive transistor Mf may be small, and it is a waste of current consumption to constantly supply the bias current corresponding to the maximum output current, and equipment using a battery is required. Etc., it was not so preferable because it shortens the battery life. Furthermore, when the bias current for the drive transistor Mf is large and the output current io is small, the response of the output transistor Mh to the change in the output voltage Vo becomes too fast and oscillation easily occurs.
Phase compensation capacitor C for stable operation
It was necessary to increase the capacity of a.

Therefore, when the maximum output current is large and the output current changes greatly and the minimum output current is small, the bias current of the drive transistor Mf is set large and the capacitance of the phase compensation capacitor Ca is also set. Had to be big. Therefore, in some cases, the phase compensating capacitor Ca may not fit in the IC chip and may be externally attached, which may hinder the miniaturization of the device.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to reduce the bias current of the drive transistor even when a load having a large fluctuation in current consumption is connected, and An object of the present invention is to obtain a constant voltage power supply circuit suitable for integration in which the capacity of the compensation capacitor can be reduced.

[0008]

A constant voltage power supply circuit according to the present invention is a constant voltage power supply circuit for generating and outputting a predetermined constant voltage based on a preset reference voltage. Output voltage detection circuit section that detects the voltage and generates and outputs a voltage according to the detected output voltage, and amplifies and outputs an error between the output voltage of the output voltage detection circuit section and the reference voltage. An error amplification circuit section,
An amplifying transistor that amplifies the output voltage from the error amplifying circuit unit and a bias circuit that supplies a bias current to the amplifying transistor, and an amplifying circuit unit that amplifies and outputs the output voltage of the error amplifying circuit unit; An output circuit section having an output transistor that outputs a current according to the output voltage of the amplification circuit section, wherein the bias circuit supplies a bias current according to the output voltage of the amplification circuit section to the amplification transistor. Is.

Specifically, the bias circuit increases the bias current when the current output from the output transistor increases, and decreases the bias current when the current output from the output transistor decreases. I did it.

The bias circuit outputs an electric current according to the output voltage of the amplifier circuit section and outputs an electric current proportional to the output current of the output transistor, and an output current detecting transistor, and the output current detecting transistor. A current mirror circuit for supplying the output current of the transistor as a bias current to the amplifying transistor is provided.

The constant voltage power supply circuit according to the present invention is
A constant voltage power supply circuit that generates a predetermined constant voltage based on a preset reference voltage and selectively outputs it from a plurality of output terminals, detects the generated and output voltage, and outputs the detected output. An output voltage detection circuit unit that generates and outputs a voltage according to a voltage, an error amplification circuit unit that amplifies and outputs an error in the output voltage of the output voltage detection circuit unit with respect to the reference voltage, and the error amplification circuit unit An amplifying transistor for amplifying an output voltage from the amplifier and a bias circuit for supplying a bias current to the amplifying transistor, and an amplifying circuit part for amplifying and outputting the output voltage of the error amplifying circuit part; An output circuit section having an output transistor that outputs a current according to the output voltage, and an output circuit that selectively outputs the output current of the output circuit section to a plurality of output terminals according to an input control signal. The bias circuit supplies a bias current according to a control signal from the control circuit unit, and the control circuit unit includes a terminal selection circuit unit and a control circuit unit that controls the operation of the output terminal selection circuit unit. The bias current output from the bias circuit is controlled according to the output terminal selected by the output terminal selection circuit section.

Specifically, when the control circuit section controls the output terminal selection circuit section to increase the current output from the output transistor, the control circuit section increases the output current with respect to the bias circuit. Accordingly, when the bias current is increased and the current output from the output transistor is decreased, the bias current is decreased with respect to the bias circuit according to the decrease of the output current.

When increasing the current output from the output transistor, the control circuit unit increases the bias current supplied from the bias circuit to a current value corresponding to the increase in the output current, and then outputs the current. The terminal selection circuit unit is controlled to increase the output current from the output transistor.

When the control circuit section reduces the current output from the output transistor, the control circuit section controls the output terminal selection circuit section to reduce the current output from the output transistor, and then the output current decreases. The bias current supplied from the bias circuit is reduced to a current value according to the above.

On the other hand, the control circuit section includes a storage section for storing a time difference between the timing of changing the bias current from the bias circuit and the timing of changing the output current from the output transistor, and the time difference is stored in advance in the storage section. May be stored in.

Further, the bias circuit is provided corresponding to a plurality of constant current sources for respectively supplying a predetermined constant current, and corresponding to each of the constant current sources, and responds according to a control signal from the control circuit section. Switch circuits for supplying a constant current from a constant current source to the amplifying transistor, and the control circuit section operates the switch circuits according to the output terminals selected by the output terminal selection circuit section. The bias current supplied to the amplification transistor is controlled.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be described in detail based on the embodiments shown in the drawings. First embodiment. FIG. 1 is a circuit diagram showing an example of a constant voltage power supply circuit according to the first embodiment of the present invention. The constant voltage power supply circuit 1 in FIG. 1 includes a reference voltage generation circuit 2 that generates and outputs a predetermined reference voltage Vr, and a voltage divider circuit 3 that divides and outputs the output voltage Vo output from the output terminal OUT. The error amplifier circuit 4 including a differential amplifier for amplifying and outputting the error of the divided voltage Vd from the voltage dividing circuit 3 with respect to the reference voltage Vr.
It has and. The voltage dividing circuit 3 constitutes an output voltage detecting circuit section.

Further, the constant voltage power supply circuit 1 has an output terminal OU.
An output transistor P1 that is a PMOS transistor that controls the current supply to T, and a PM that controls the operation of the output transistor P1 according to the output signal of the error amplification circuit 4.
Drive transistor P2 consisting of an OS transistor
A bias circuit 5 for supplying a bias current to the drive transistor P2, and a phase correction capacitor C1. The drive transistor P2 and the bias circuit 5 form an amplification circuit section that amplifies and outputs the output signal of the error amplification circuit 4, and the drive transistor P2
Is an amplifying transistor. The output transistor P1 forms an output circuit unit that outputs a current according to the signal amplified by the amplifier circuit unit and keeps the voltage of the output terminal constant.

The voltage dividing circuit 3 is composed of a series circuit of resistors R1 and R2 connected between the output terminal OUT and the ground voltage, and the divided voltage Vd is output from the connecting portion of the resistors R1 and R2. . A phase compensation capacitor C1 is connected in parallel with the resistor R1. Next, the error amplification circuit 4
PMOS transistor P forming a current mirror circuit
3 and P4 and NMOS transistors N1 to N3, and the NMOS transistors N1 and N2 form a differential pair. The sources of the NMOS transistors N1 and N2 are connected, and the NMOS is connected between the connection and the ground voltage.
The transistor N3 is connected.

The PMOS transistor P3 is connected between the input terminal IN to which the input voltage Vi is input and the drain of the NMOS transistor N1.
Between N and the drain of the NMOS transistor N2,
The PMOS transistor P4 is connected. PMOS
The gates of the transistors P3 and P4 are connected, and the connection portion is connected to the drain of the PMOS transistor P3.

At the gate of the NMOS transistor N3,
A predetermined constant voltage Vb is applied and the NMOS transistor N3 forms a constant current source. A predetermined reference voltage Vr from the reference voltage generating circuit 2 is input to the gate of the NMOS transistor N1, and a divided voltage Vd from the voltage dividing circuit 3 is input to the gate of the NMOS transistor N2. The connection between the PMOS transistor P4 and the NMOS transistor N2 forms the output end of the error amplification circuit 4, and the output end is connected to the gate of the drive transistor P2.

The bias circuit 5 is composed of a PMOS transistor P5 and NMOS transistors N4 and N5 forming a current mirror circuit. In addition, PMOS
The transistor P5 serves as an output current detecting transistor. The PMOS transistor P5 and the NMOS transistor N4 are connected in series between the input terminal IN and the ground voltage, and the gate of the PMOS transistor P5 is connected to the drain of the PMOS transistor P2.

Gates of the NMOS transistors N4 and N5 are connected to each other, and the connection portion is connected to the NMOS transistor N4.
Connected to the drain of. On the other hand, input terminals IN and N
The drive transistor P2 is connected between the drain of the MOS transistor N5 and the output transistor P1 is connected between the input terminal IN and the output terminal OUT. The gate of the output transistor P1 is connected to the connection between the drive transistor P2 and the NMOS transistor N5.

In such a structure, a voltage corresponding to the current output from the drive transistor P2 is input to the gate of the output transistor P1, and the load 8 of the output transistor P1 changes and the output current io changes. Also in this case, the output current io is controlled so that the output voltage Vo becomes constant. The drive circuit P2 is supplied with a bias current proportional to the output current io by the bias circuit 5.

In the bias circuit 5, the PMOS transistor P5 is for detecting the current output from the output transistor P1.
A device having a smaller size and a smaller current supply capability is used and outputs a current proportional to the current output from the output transistor P1. The current output from the PMOS transistor P5 is input to the drain of the input-side NMOS transistor N4 in the current mirror circuit. Therefore, a current proportional to the output current io is supplied as the bias current of the drive transistor P2 via the NMOS transistor N5 on the output side of the current mirror circuit.

As described above, the constant voltage power supply circuit according to the first embodiment is proportional to the output current io with respect to the drive transistor P2 that drives the output transistor P1 according to the output signal of the error amplification circuit 4. A bias circuit 5 for supplying a bias current is provided. Therefore, even when a load with large fluctuation in current consumption is connected, the bias current of the drive transistor can be reduced, so the capacitance of the phase compensation capacitor can be reduced and integration can be facilitated. You can

Second Embodiment. In the first embodiment, the drive transistor P2 is output according to the output current io.
However, when the output current io changes according to the switching of the load to be connected, a plurality of constant current sources that supply the bias current to the drive transistor according to the switching of the load are changed. The switching control may be performed to change the bias current for the drive transistor. Such a configuration is the second embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of a constant voltage power supply circuit according to the second embodiment of the present invention. In FIG. 2, the same parts as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted and only the differences from FIG. 1 will be described. 2 is different from FIG. 1 in that the bias circuit 5 of FIG. 1 is changed to a circuit configuration in which the bias current value can be changed to be a bias circuit 15, and a switching circuit 16 for switching power supply to a plurality of output terminals is provided. The control circuit 17 controls the switching of the switching circuit 16 and controls the current supply amount of the bias circuit 15 in accordance with the switching control. Accordingly, the constant voltage power supply circuit 1 of FIG.
Is the constant voltage power supply circuit 11.

The constant voltage power supply circuit 11 in FIG. 2 includes a reference voltage generating circuit 2, a voltage dividing circuit 3, an error amplifying circuit 4, and
Output transistor P1 and drive transistor P2
And a bias circuit 15 for controlling a bias current supplied to the drive transistor P2 according to the input control signal, and a phase correction capacitor C1. Further, the constant voltage power supply circuit 11 includes a switching circuit 16 that switches current supply to a plurality of loads according to an input control signal, and a bias circuit 15 and a control circuit 17 that controls the operation of the switching circuit 16. ing. The switching circuit 1
Reference numeral 6 forms an output terminal selection circuit section.

The bias circuit 15 is composed of NMOS transistors N11 to N13 and electronic switches S1 to S3 including analog switches. Electronic switch S
Each of 1 to S3 forms a switch circuit. Between the drain of the drive transistor P2 and the ground voltage, a series circuit of an electronic switch S1 and an NMOS transistor N11,
Series circuit of electronic switch S2 and NMOS transistor N12, and electronic switch S3 and NMOS transistor N
Thirteen series circuits are connected in parallel.

The electronic switches S1 to S3 are connected to the control circuit 17
Corresponding control signals o1 to o3 are respectively input to the control signal input terminals, and when a high-level signal is input to the control signal input terminals, they are turned on (ON) to be in a conductive state, and the control signal input terminals are low-level. Is turned off when the signal of
F) and it becomes a cutoff state. NMOS transistor N11
Each of N13 to N13 forms a constant current source because a predetermined constant voltage Vb is input to each gate, and each current supply capability may be the same or different. Also,
The constant current supplied by the NMOS transistor N11 is i1,
The constant current supplied by the NMOS transistor N12 is i2,
The constant current supplied by the NMOS transistor N13 is i3.

Next, the switching circuit 16 is composed of electronic switches S4 to S6 composed of analog switches and the like.
When the connecting portion between the output transistor P1 and the resistor R1 is X, an electronic switch S4 is provided between the connecting portion X and the first output terminal OUT1 and an electronic switch S5 is provided between the connecting portion X and the second output terminal OUT2. , The connection portion X and the third output terminal OUT3
And the electronic switches S6 are connected between them.
Also in the electronic switches S4 to S6, the corresponding control signals o4 to o6 are input from the control circuit 17 to the control signal input terminals, respectively, and when a high level signal is input to the control signal input terminals, the switches are turned on and become conductive. When a low-level signal is input to the control signal input terminal, it turns off and enters a cutoff state.

The control circuit 17 includes electronic switches S4 to S6.
To selectively switch the power supply to the loads 8a to 8c connected to the first output terminal OUT1 to the third output terminal OUT3. At the same time, the control circuit 17
Switching control of the electronic switches S1 to S3 of the bias circuit 15 is performed according to the switching of the electronic switches S4 to S6. That is, the control circuit 17 controls the output transistor P1.
The bias circuit 15 responds to the change in the current output from the bias circuit 15.
To change the bias current value supplied to the drive transistor P2. Note that the current flowing through the load 8a is i
4, the current flowing through the load 8b is i5, and the current flowing through the load 8c is i6. Also, the output terminals OUT1 to OUT
The respective voltages Vo1 to Vo3 of 3 become the same voltage and become constant at a predetermined value.

FIG. 3 is a diagram showing an example of changes in the bias current to the drive transistor P2 with respect to changes in the output current, which is the drain current of the output transistor P1,
FIG. 4 is a diagram showing the operation of the electronic switches S1 to S6 in the case of FIG. A control example of the bias circuit 15 and the switching circuit 16 by the control circuit 17 will be described with reference to FIGS. 3 and 4.

In the zones Z1 and Z5, the control circuit 17
Turns on only the electronic switch S4 in the switching circuit 16 to bring it into a conductive state, and at the same time, the electronic switches S4 and S4.
5 is turned off to cut off each. The control circuit 17 also controls the output transistor P1 to the first output terminal OU.
In the bias circuit 15, the electronic switch S1 is turned on so as to be in a conductive state, and the electronic switches S2 and S3 are turned off so that a bias current corresponding to the current i4 flowing through the load 8a is supplied via T1. To By doing so, the bias current of the constant current i1 is supplied to the drive transistor P2 by the bias circuit 15.

Next, in the zone Z2, the control circuit 17
In the switching circuit 16, the electronic switches S4 and S5 are turned on to make them conductive, and the electronic switch S6 is turned on.
To turn it off to cut it off. In addition, the control circuit 17
The current (i4 + i) output from the output transistor P1
In order to supply the bias current according to 5), the electronic switches S1 and S2 in the bias circuit 15 are turned on to bring them into conduction, and the electronic switch S3 is turned off into a cutoff state. By doing so, the bias current of the constant current (i1 + i2) is supplied to the drive transistor P2 by the bias circuit 15.

Next, in the zone Z3, the control circuit 17
In the switching circuit 16, the electronic switches S4 to S6 are turned on to bring them into conduction. In addition, the control circuit 17
The current (i4 + i5) output from the output transistor P1
In order to supply the bias current corresponding to + i6), the electronic switches S1 to S3 in the bias circuit 15 are turned on to bring them into a conductive state. By doing so, the bias current of the constant current (i1 + i2 + i3) is supplied to the drive transistor P2 by the bias circuit 15.

Next, in the zone Z4, the control circuit 17
In the switching circuit 16, the electronic switches S4 and S6 are turned on to bring them into conduction, and
Turn off 5 to shut off. In addition, the control circuit 17
Is the current (i4 +) output from the output transistor P1.
In order to supply a bias current corresponding to i6), the electronic switches S1 and S3 in the bias circuit 15 are turned on to be in a conductive state, and the electronic switch S2 is turned off to be in a cutoff state. By doing so, the bias current of the constant current (i1 + i3) is supplied to the drive transistor P2 by the bias circuit 15.

Further, as can be seen from FIG. 3, the control circuit 1
When the electronic switches S4 to S6 are switched to increase the output current of the output transistor P1, a bias current according to the value when the output current of the output transistor P1 is increased is switched before switching the electronic switches S4 to S6. The electronic switches S1 to S3 of the bias circuit 15 are switched first so as to be supplied to the drive transistor P2.

Further, the control circuit 17 includes an electronic switch S4.
~ S6 is switched to decrease the output current of the output transistor P1, the electronic switches S4 to S6 are switched to increase the output current of the output transistor P1, and then the output current of the output transistor P1 is increased. The electronic switches S1 to S3 of the bias circuit 15 are switched so that the bias current is supplied to the drive transistor P2. By doing so, the bias current for the drive transistor P2 becomes insufficient,
The voltage V of the first output terminal OUT1 to the third output terminal OUT3
It is possible to prevent o1 to Vo3 from decreasing.

Further, the loads 8a to 8 by the control circuit 17
The time difference between the timing of switching c and the timing of switching the bias current of the bias circuit 15 takes into account the response time of the constant voltage power supply circuit 11, and the first output terminal OUT1
-Measurement is made in advance for each combination of switching of the loads 8a to 8c so that the fluctuation of each voltage of the third output terminal OUT3 is small and the time for supplying an excessive bias current to the drive transistor P2 is short. Each time obtained by measurement is stored in advance in a storage unit (not shown) of the control circuit 17. The control circuit 17 shifts the switching timing of the load and the bias current of the bias circuit 15 according to the time stored in the storage unit.

On the other hand, in FIG. 2, the bias circuit 1 is selected according to the combination of power supply to the loads 8a to 8c.
It is possible to reduce the number of NMOS transistors forming the constant current source of No. 5. For example, when the current output from the output transistor P1 is the same in the zones Z2 and Z4 in FIGS. 2 to 4, the constant voltage power supply circuit 11 in FIG.
Is as shown in FIG. The constant voltage power supply circuit 11 of FIG. 5 differs from that of FIG. 2 in the bias circuit 15.
This is because the NMOS transistor N13 and the electronic switch S3 have been eliminated.

FIG. 6 shows the output transistor P in FIG.
FIG. 7 is a diagram showing an example of changes in the bias current to the drive transistor P2 with respect to changes in the output current which is the drain current of No. 1, and FIG. 7 shows the operation of the electronic switches S1, S2, S4 to S6 in the case of FIG. It is the figure shown. Figure 6
6 and 7, a control example of the bias circuit 15 and the switching circuit 16 by the control circuit 17 of FIG. 5 will be described. The operation of the zones Z1 and Z5 is the same as in the case of FIG. 2, and therefore its explanation is omitted.

In the zones Z2 and Z4, the control circuit 17
In the switching circuit 16, the electronic switches S4 and S5 are turned on to make them conductive, and the electronic switch S6 is turned off to make them cut off. In addition, the control circuit 17
Is the current (i4 +) output from the output transistor P1.
In order to supply the bias current corresponding to i5), the electronic switch S2 in the bias circuit 15 is turned on to make it conductive, and the electronic switch S1 is turned off to be cut off. By doing so, the bias current of the constant current i2 is supplied to the drive transistor P2 by the bias circuit 15.

Next, in the zone Z3, the control circuit 17
In the switching circuit 16, the electronic switches S4 to S6 are turned on to bring them into conduction. In addition, the control circuit 17
The current (i4 + i5) output from the output transistor P1
In order to supply the bias current according to + i6), the electronic switches S1 and S2 in the bias circuit 15 are turned on to bring them into a conductive state. By doing so, the drive transistor P2 is connected to the bias circuit 15
Supplies a constant current (i1 + i2) bias current.

Also in this case, as can be seen from FIG. 6, the control circuit 17 has the electronic switch S.
When switching 4 to S6 to increase the output current of the output transistor P1, before switching the electronic switches S4 to S6, a bias current corresponding to the value when the output current of the output transistor P1 increases is set to the drive transistor P2.
Switch S of the bias circuit 15 to be supplied to
First, S2 is switched.

Further, the control circuit 17 uses the electronic switch S4.
~ S6 is switched to decrease the output current of the output transistor P1, the electronic switches S4 to S6 are switched to increase the output current of the output transistor P1, and then the output current of the output transistor P1 is increased. The electronic switches S1 and S2 of the bias circuit 15 are switched so that the bias current is supplied to the drive transistor P2. By doing so, the bias current for the drive transistor P2 becomes insufficient,
The voltage V of the first output terminal OUT1 to the third output terminal OUT3
It is possible to prevent o1 to Vo3 from decreasing.

That is, the bias current value of the bias circuit 15 is set to some basic value, and the combination thereof is changed, so that the kind of the current value output from the output transistor P1 with a small constant current source. Can correspond to. The basic value of the bias current value may be set to be an exponential multiple of 2, such as 1, 2, 4, 8 or the specific load current changes depending on the loads 8a to 8c. If so, it may be set according to the load current. Constant voltage power supply circuit 1 shown in FIG. 5 to FIG.
According to 1, when the current i1 flowing in the NMOS transistor N11 is set to 1, the current i2 flowing in the NMOS transistor N12 is set to 2, so that three kinds of bias currents can be set.

In this way, it is possible to reduce the number of NMOS transistors forming the constant current source of the bias circuit 15 and the electronic switches corresponding to the NMOS transistors.
The cost can be reduced. The control circuit 17
The time difference between the timing of switching the loads 8a to 8c and the timing of switching the bias current of the bias circuit 15 is stored in the control circuit 17 in advance as in the case of the constant voltage power supply circuit 11 of FIG.

As described above, in the constant voltage power supply circuit according to the second embodiment, the control circuit 17 switches the drive transistor P2 that drives the output transistor P1 according to the output signal of the error amplification circuit 4. By turning on each electronic switch of the bias circuit 15 according to the electronic switches S4 to S6 to be turned on of the circuit 16, the switching circuit 16 outputs the first output terminal OUT1 to the third output terminal OUT.
A bias current corresponding to a current flowing through the loads 8a to 8c connected to the drive circuit 3 is supplied from the bias circuit 15 to the drive transistor P2. From this, when the power is selectively supplied to the plurality of loads, the same effect as that of the first embodiment can be obtained.

In the second embodiment, the constant voltage power supply circuit 11 has been described by taking as an example the case where the loads 8a to 8c respectively corresponding to the three output terminals are connected.
This is an example, and the present invention is not limited to this and is applied to the case where loads corresponding to a plurality of output terminals are connected. In addition, the first and second
In each of the above embodiments, the case where the bias voltage Vb is input from the outside of the constant voltage power supply circuit has been described as an example, but a circuit for generating and outputting the bias voltage Vb should be provided in the constant voltage power supply circuit. You may

Third Embodiment. In the second embodiment, when the current output from the output transistor P1 changes according to the switching of the connected load, the control circuit 17 controls the drive transistor P2 according to the switching of the load. Switching control of a plurality of constant current sources for supplying a bias current is performed, and drive transistor P2
The bias current to the drive transistor P2 may be changed, but the gate voltage of the output transistor P1 may be detected, and the bias current to the drive transistor P2 may be changed according to the detected gate voltage. This is a third embodiment of the invention.

FIG. 9 is a circuit diagram showing an example of a constant voltage power supply circuit according to the third embodiment of the present invention. In FIG. 9, the same or similar parts as those in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted here and only the differences from FIG. 2 will be described. The difference between FIG. 9 and FIG. 2 is that
The bias circuit 1 shown in FIG. 2 is a detection circuit 22 that detects the gate voltage of the output transistor P1 and controls the switching of the electronic switches S1 to S3 according to the detected gate voltage.
5, the bias circuit 25 is provided, and accordingly, the constant voltage power supply circuit 11 of FIG.
There is something I did.

The constant voltage power supply circuit 21 shown in FIG. 9 includes a reference voltage generating circuit 2, a voltage dividing circuit 3, an error amplifying circuit 4, and
Output transistor P1 and drive transistor P2
And a bias circuit 25 for controlling a bias current supplied to the drive transistor P2 according to the input control signal, and a phase correction capacitor C1. Further, the constant voltage power supply circuit 21 switches the current supply to a plurality of loads according to the input control signal, and the control circuit 17 that controls the operation of the switching circuit 16.
It has and.

The bias circuit 25 is composed of NMOS transistors N11 to N13, electronic switches S1 to S3, and a detection circuit 22 for controlling switching of the electronic switches S1 to S3. The detection circuit 22 includes electronic switches S1 to S depending on the gate voltage of the output transistor P1.
3 switching control is performed. Here, the output transistor P when the current i4 flows from the output transistor P1
1 is Vg1, the gate voltage of the output transistor P1 when the current (i4 + i5) flows from the output transistor P1 is Vg2, and the output transistor P1 is
Vg3 is the gate voltage of the output transistor P1 when the current (i4 + i5 + i6) flows from the output transistor P1 and Vg4 is the gate voltage of the output transistor P1 when the current (i4 + i6) flows from the output transistor P1.

In the zones Z1 and Z5 shown in FIG. 3 in which the gate voltage of the output transistor P1 is Vg1, the detection circuit 22 turns on the electronic switch S1 and turns off the electronic switches S2 and S3, respectively, and causes the drive transistor P2 to operate. The bias current of the current i1 is supplied. Further, the detection circuit 22 includes an output transistor P
Zone Z2 shown in FIG. 3 in which the gate voltage of 1 becomes Vg2
Then, the electronic switches S1 and S2 are turned on and the electronic switch S3 is turned off so that the bias current of the current (i1 + i2) is supplied to the drive transistor P2.

Further, in the detection circuit 22, the gate voltage of the output transistor P1 becomes Vg3, the zone Z shown in FIG.
In 3, the electronic switches S1 to S3 are turned on,
Current (i1 + i2 + i3) in drive transistor P2
So that the bias current of is supplied. Further, in the detection circuit 22, the gate voltage of the output transistor P1 is Vg4.
In the zone Z4 shown in FIG. 3, the electronic switch S1
And S3 are turned on, and the electronic switch S2 is turned on.
Is turned off, and the current (i1 +
The bias current of i3) is supplied.

On the other hand, also in FIG. 9, the loads 8a to 8c are provided.
It is possible to reduce the number of NMOS transistors forming the constant current source of the bias circuit 25 according to the combination of the power supply to the. For example, as shown in FIGS. 6 and 7, when the current output from the output transistor P1 is the same in the zone Z2 and the zone Z4, the constant voltage power supply circuit 21 of FIG. 9 becomes as shown in FIG. . The constant voltage power supply circuit 21 of FIG. 10 differs from that of FIG. 9 in that the bias circuit 25 does not include the NMOS transistor N13 and the electronic switch S3.

In the case of FIG. 10, the detection circuit 22 controls the electronic switch S in the zones Z1 and Z5 shown in FIGS.
1 is turned on and the electronic switch S2 is turned off. In the zones Z2 and Z4 shown in FIGS. 6 and 7, the electronic switch S2 is turned on.
1 is turned off and the electronic switch S2 is turned on. Also,
The detection circuit 22 turns on the electronic switches S1 and S2 in the zone Z3 shown in FIGS. 6 and 7, respectively.

As described above, the constant voltage power supply circuit according to the third embodiment monitors the gate voltage of the output transistor P1 and changes the bias current supplied to the drive transistor P2 according to the gate voltage value. The detection circuit 22 that controls switching of each electronic switch of the bias circuit 25 is provided. From this, when the constant voltage power supply circuit and the control circuit are formed on different chips, it is possible to reduce each terminal for connecting each electronic switch of the bias circuit and the control circuit, and to reduce the chip size and The cost can be reduced.

Needless to say, the current values of the bias currents i1 and i2 shown in FIG. 6 are not necessarily the same as the current values of the bias currents i1 and i2 shown in FIG.

[0062]

As is apparent from the above description, according to the constant voltage power supply circuit of the present invention, the bias circuit supplies a bias current corresponding to the output voltage of the amplification circuit section to the amplification transistor, Specifically, when the current output from the output transistor increases, the bias current is increased, and when the current output from the output transistor decreases, the bias current is decreased. Therefore, even when connecting a load with a large fluctuation in consumption current, the bias current of the amplifying transistor that drives the output transistor is changed according to the load current, so that the consumption current is small and the phase compensation capacitor is small. It is possible to realize a constant voltage power supply circuit that can reduce the capacity of the device, can be easily integrated into an IC, and has a fast response speed.

Further, the bias circuit outputs a current according to the output voltage of the amplifier circuit section to output a current proportional to the output current of the output transistor, and an output current detection transistor, and the output current detection transistor. The current mirror circuit supplies the output current as a bias current to the amplifying transistor. Therefore, even when a load with a large fluctuation in current consumption is connected, the bias current of the amplification transistor that drives the output transistor can be changed with a simple circuit according to the load current.

On the other hand, the bias circuit supplies a bias current according to the control signal from the control circuit section, and the control circuit section outputs from the bias circuit according to the output terminal selected by the output terminal selection circuit section. When the current output from the output transistor is increased, the bias current is increased with respect to the bias circuit according to the increase of the output current.
When decreasing the current output from the output transistor, the bias current is decreased in the bias circuit in accordance with the decrease in the output current. Therefore, when power is selectively supplied to a plurality of loads, the bias current of the amplifying transistor that drives the output transistor is changed according to the load current, resulting in low current consumption and phase compensation. It is possible to reduce the capacity of the capacitor for use in the IC, easily realize an IC, and to realize a constant voltage power supply circuit with a fast response speed.

When increasing the current output from the output transistor, the output terminal selection circuit section is controlled after increasing the bias current supplied from the bias circuit to a current value corresponding to the increase in the output current. In order to increase the output current from the output transistor and decrease the current output from the output transistor, after controlling the output terminal selection circuit unit to decrease the current output from the output transistor, The bias current supplied from the bias circuit is reduced to a current value corresponding to the decrease in output current. Therefore, it is possible to prevent the output voltage from decreasing due to the shortage of the bias current to the amplifying transistor.

Since the time difference between the timing of changing the bias current from the bias circuit and the timing of changing the output current from the output transistor is stored in advance in the storage unit of the control circuit unit, the amplifying transistor It is possible to reliably prevent the output voltage from decreasing due to the shortage of the bias current for the output voltage.

Specifically, a bias circuit is provided for each of a plurality of constant current sources for supplying a predetermined constant current and each of the constant current sources, and is provided in accordance with a control signal from the control circuit. Each switch circuit supplies a constant current from a corresponding constant current source to the amplifying transistor. From this, even when the power is selectively supplied to a plurality of loads with a simple circuit, the current consumption is small, and further, the capacity of the phase compensation capacitor can be reduced, and it is easy to form an IC. A constant voltage power supply circuit with a fast response speed can be realized.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an example of a constant voltage power supply circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of a constant voltage power supply circuit according to a second embodiment of the present invention.

FIG. 3 is a diagram showing an example of changes in bias current to the drive transistor P2 with respect to changes in output current of the output transistor P1 in FIG.

FIG. 4 shows electronic switches S1 to S6 in the case of FIG.
It is a figure showing the operation of.

FIG. 5 is a circuit diagram showing another example of the constant voltage power supply circuit according to the second embodiment of the present invention.

FIG. 6 is a diagram showing an example of changes in the bias current to the drive transistor P2 with respect to changes in the output current of the output transistor P1 in FIG.

FIG. 7 shows electronic switches S1 and S in the case of FIG.
It is a figure showing operation of 2, S4-S6.

FIG. 8 is a circuit diagram showing an example of a conventional constant voltage power supply circuit.

FIG. 9 is a circuit diagram showing an example of a constant voltage power supply circuit according to a third embodiment of the present invention.

FIG. 10 is a circuit diagram showing another example of the constant voltage power supply circuit according to the third embodiment of the present invention.

[Explanation of symbols]

1,11 constant voltage power supply circuit 2 Reference voltage generation circuit 3 voltage divider 4 Error amplification circuit 5,15 Bias circuit 8,8a-8c load 16 Switching circuit 17 Control circuit P1 output transistor P2 drive transistor

Claims (9)

[Claims] 1. A constant voltage power supply circuit that generates and outputs a predetermined constant voltage based on a preset reference voltage, detects the generated and output voltage, and responds to the detected output voltage. An output voltage detection circuit section that generates and outputs a voltage, an error amplification circuit section that amplifies and outputs an error in the output voltage of the output voltage detection circuit section with respect to the reference voltage, and an output from the error amplification circuit section. An amplifying transistor for amplifying a voltage and a bias circuit for supplying a bias current to the amplifying transistor, and an amplifying circuit unit for amplifying and outputting an output voltage of the error amplifying circuit unit; and an output voltage of the amplifying circuit unit. An output circuit section having an output transistor that outputs a current according to the bias circuit, wherein the bias circuit supplies a bias current according to the output voltage of the amplification circuit section to the amplification transistor. Constant voltage power supply circuit, characterized by. 2. The bias circuit increases the bias current when the current output from the output transistor increases, and decreases the bias current when the current output from the output transistor decreases. The constant voltage power supply circuit according to claim 1. 3. The output current detecting transistor, wherein the bias circuit outputs a current according to the output voltage of the amplifier circuit section and outputs a current proportional to the output current of the output transistor, and the output current detecting transistor. 3. A current mirror circuit that supplies the output current of a transistor as a bias current to the amplifying transistor.
Constant voltage power supply circuit described. 4. A constant voltage power supply circuit which generates a predetermined constant voltage based on a preset reference voltage and selectively outputs the voltage from a plurality of output terminals, and detects the generated and output voltage. An output voltage detection circuit unit that generates and outputs a voltage according to the detected output voltage; and an error amplification circuit unit that amplifies and outputs an error in the output voltage of the output voltage detection circuit unit with respect to the reference voltage, An amplifying transistor that amplifies the output voltage from the error amplifying circuit unit and a bias circuit that supplies a bias current to the amplifying transistor, and an amplifying circuit unit that amplifies and outputs the output voltage of the error amplifying circuit unit; An output circuit section having an output transistor that outputs a current according to the output voltage of the amplifier circuit section, and an output current of the output circuit section is selected to a plurality of output terminals according to an input control signal. A control circuit unit for performing an output terminal selection circuit for output, the operation control of the output terminal selection circuit section,
The bias circuit supplies a bias current according to a control signal from the control circuit unit, and the control circuit unit outputs the bias current according to the output terminal selected by the output terminal selection circuit unit. A constant voltage power supply circuit characterized in that it controls a bias current. 5. The control circuit section, when increasing the current output from the output transistor by controlling the output terminal selection circuit section, biases the bias circuit according to the increase of the output current. Increase the current,
5. When decreasing the current output from the output transistor, the bias current is decreased with respect to the bias circuit according to the decrease of the output current.
Constant voltage power supply circuit described. 6. The control circuit unit, when increasing the current output from the output transistor, increases the bias current supplied from the bias circuit to a current value corresponding to the increase of the output current, and then outputs the current. 6. The constant voltage power supply circuit according to claim 5, wherein the terminal selection circuit unit is controlled to increase the output current from the output transistor. 7. The control circuit unit, when reducing the current output from the output transistor, controls the output terminal selection circuit unit to reduce the current output from the output transistor and then reduces the output current. 7. The constant voltage power supply circuit according to claim 5, wherein the bias current supplied from the bias circuit is reduced to a current value according to the above. 8. The control circuit unit includes a storage unit that stores a time difference between the timing of changing the bias current from the bias circuit and the timing of changing the output current from the output transistor, and the time difference is stored in advance in the storage unit. The constant voltage power supply circuit according to claim 6 or 7, wherein the constant voltage power supply circuit is stored in. 9. The bias circuit includes a plurality of constant current sources that respectively supply a predetermined constant current, and the bias circuits are provided so as to correspond to the constant current sources, and correspond to the control signals from the control circuit section. And a switch circuit that supplies a constant current from a constant current source to the amplifying transistor, and the control circuit unit operates the switch circuit according to the output terminal selected by the output terminal selection circuit unit. 9. The constant voltage power supply circuit according to claim 4, wherein the bias current supplied to the amplifying transistor is controlled.