JP4642827B2 - Constant voltage power supply - Google Patents

Description

  The present invention relates to a constant voltage power supply apparatus that can respond to a change in output voltage due to a transient change in a load at a high speed and can operate with a low current consumption.

  Conventionally, as a configuration of a constant voltage power supply device that converts an input voltage into a predetermined constant voltage and outputs it, the output voltage is usually controlled by comparing the output voltage with a reference voltage and minimizing the difference voltage. Feedback is applied to the output control transistor. For this reason, a change in the output voltage is transmitted to the output control transistor, and some time is required to restore the output voltage to a predetermined voltage value. The time required for such transmission is delayed in response. If the response delay is large, the output voltage also fluctuates greatly when the load current fluctuates greatly. In the worst case, the circuit forms a load connected to the output terminal from which the output voltage is output. There was a possibility that the load would be less than the guaranteed operating voltage.

  Many of such response delays are determined by the inter-wiring capacitance in the control circuit of the constant voltage power supply device, the parasitic capacitance between the electrodes of the transistor, and the current value for charging and discharging these capacitances. That is, in order to increase the response speed, such a capacity may be reduced or a current value for charging and discharging such a capacity may be increased. However, since such a capacitance is almost determined by the layout of the IC constituting the control circuit and the size of the transistor necessary for controlling the output current, the charge / discharge current value is usually set. There was a way to make it bigger.

  However, increasing the charge / discharge current value means increasing the bias current value of the control circuit in the constant voltage power supply device, and inevitably increases the current consumption of the power supply device itself. In recent years, in consideration of environmental problems, power saving of electric devices has been demanded, and such a tendency is particularly remarkable in devices driven by batteries. For this reason, it is desirable to operate the control circuit of the constant voltage power supply apparatus with as low a current as possible.

Therefore, there has been a technique for improving the response speed of the output voltage in the constant voltage power supply device as shown in FIG. 8 (see, for example, Patent Document 1).
In FIG. 8, a current supply circuit 130 and a current absorption circuit 140 are connected to the voltage output terminal TO of the feedback voltage supply source 110.

  The power supply circuit 130 includes a voltage source 131 that generates a voltage VL slightly lower than a steady voltage at the voltage output terminal TO, a first diode 133 having a cathode connected to the voltage output terminal TO, and a cathode connected to the voltage source 131. The connected second diode 134 and a current source 132 having a current output terminal connected to the connection point of the anode of each of the first and second diodes.

  The current suction circuit 140 includes a voltage source 141 that outputs a voltage VH that is slightly higher than the steady voltage of the voltage output terminal TO, a third diode 143 that has an anode connected to the voltage output terminal TO, and an anode that is a voltage source. 141 and a fourth diode 144 connected to 141, and a current source 142 whose current output terminal is connected to the connection point of the respective cathodes of the third and fourth diodes.

While the voltage of each voltage source and the voltage output terminal TO maintains the relationship of VH>Vo> VL, the output current of the current source 132 flows to the voltage source 131 and the output current of the current source 142 flows to the voltage source 141. No current flows through the voltage output terminal TO. Here, when the voltage Vo at the voltage output terminal TO decreases and Vo <VL, current is supplied from the current source 132 to the voltage output terminal TO, and the voltage Vo at the voltage output terminal TO becomes equal to or lower than the voltage VL. To prevent. Similarly, when the voltage Vo at the voltage output terminal TO rises and VH <Vo, the current source 142 draws current from the voltage output terminal TO, and the voltage Vo at the voltage output terminal TO becomes equal to or higher than the voltage VH. To prevent. In this way, voltage fluctuation due to response delay of the voltage Vo can be suppressed.
JP-A-10-124159

  However, in FIG. 8, while the voltage Vo at the voltage output terminal TO maintains the relationship of VH> Vo> VL, the current source 132 and the current source 142 are operating, and the current is wasted. Therefore, there is a problem that the power supply efficiency is extremely lowered.

  The present invention has been made to solve the above-described problem, and a constant voltage power supply device capable of improving the response speed of an output voltage while suppressing current consumption in a control circuit of the constant voltage power supply device. The purpose is to obtain.

A constant voltage power supply device according to the present invention is a constant voltage power supply device that converts a voltage input from a DC power supply into a predetermined DC voltage and outputs it from an output terminal.
A reference voltage generation circuit that generates and outputs a predetermined reference voltage;
A voltage dividing circuit for dividing and outputting the voltage of the output terminal;
An output control transistor that performs output control of a current supplied from the DC power supply according to an input control signal;
A driver transistor that performs drive control of the output control transistor in accordance with an input control signal;
An error amplifier for controlling the operation of the driver transistor so that the divided voltage from the voltage dividing circuit unit becomes the reference voltage;
A constant current circuit unit which supplies a constant current corresponding to an input control signal to the driver transistor and forms a load of the driver transistor;
A current control circuit unit that detects an output voltage of the error amplifier and performs operation control of the constant current circuit unit so that a constant current that changes in an analog manner according to the detected output voltage is output;
Equipped with a,
The current control circuit unit is configured to increase the current value of the constant current when the output voltage of the error amplifier decreases with respect to the constant current circuit unit .

  The constant current circuit unit is formed of a MOS transistor that outputs a current corresponding to a voltage input to a gate, and the current control circuit unit is configured to output a gate voltage of the MOS transistor according to an output voltage of the error amplifier. May be controlled.

  The current control circuit unit may limit the current value output from the constant current circuit unit so as not to exceed a predetermined value.

  According to the constant voltage power supply device of the present invention, the current value of the load current of the driver transistor is changed according to the output voltage of the error amplifier. Specifically, the driver transistor is changed according to the decrease of the output voltage of the error amplifier. The load current was increased. From this, it is possible to reduce the current consumption of the constant-voltage power supply device during normal operation, and further, it is possible to shorten the return response time when the output voltage decreases, and to increase the speed of the return response. be able to.

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 device according to the first embodiment of the present invention.
In FIG. 1, a voltage Vbat from a DC power supply 10 such as a battery is input to the input terminal IN of the constant voltage power supply device 1, and a load 11 is connected to the output terminal OUT of the constant voltage power supply device 1. The constant voltage power supply device 1 generates a predetermined constant voltage Vx from the input voltage Vbat and outputs it to the load 11.

  The constant voltage power supply device 1 includes a reference voltage generating circuit unit 2 that generates and outputs a predetermined reference voltage Vr, a voltage dividing circuit unit 3 including resistors R1 and R2 that divides and outputs the output voltage Vout, and a gate. An output control transistor M1 including a P-channel MOS transistor (hereinafter referred to as a PMOS transistor) that outputs a current corresponding to the input voltage to the output terminal OUT is provided.

  Furthermore, the constant voltage power supply apparatus 1 amplifies and outputs a difference voltage of the divided voltage Vd generated by the voltage dividing circuit unit 3 with respect to the reference voltage Vr, and an output voltage of the error amplifier A1. A driver transistor M2 composed of a PMOS transistor for driving the output control transistor M1, a constant current circuit unit 4 constituting a load of the driver transistor M2, and a current value ia supplied by controlling the operation of the constant current circuit unit 4 And a current control circuit unit 5 for changing the current.

  In the error amplifier A1, the reference voltage Vr is input to the non-inverting input terminal, the divided voltage Vd is input to the inverting input terminal, and the output terminal is connected to the gate of the driver transistor M2. The source of the driver transistor M2 is connected to the input terminal IN, and the constant current circuit unit 4 is connected between the drain of the driver transistor M2 and the ground voltage. The drain of the driver transistor M2 is connected to the gate of the output control transistor M1, and the output control transistor M1 is connected between the input terminal IN and the output terminal OUT.

  On the other hand, the current control circuit unit 5 operates with the voltage Vbat as a power source, the input terminal is connected to the output terminal OUT, and a control signal for controlling the output current is output from the output terminal to the constant current circuit unit 4. The constant current circuit section 4 supplies a current ia corresponding to the control signal to the driver transistor M2.

  In such a configuration, when the state of the load 11 changes, the output current to the load 11 increases and the output voltage Vout decreases, the divided voltage Vd input to the inverting input terminal of the error amplifier A1 decreases. As a result, the output voltage of the error amplifier A1 rises and the gate voltage of the driver transistor M2 rises. For this reason, the drain voltage of the driver transistor M2 decreases, the gate voltage of the output control transistor M1 decreases, and the drain current of the output control transistor M1 increases. Therefore, the output voltage Vout increases and reaches a predetermined constant voltage. It is controlled to be Vx.

  However, it takes some time after the output voltage Vout decreases to return to the predetermined constant voltage Vx. Most of the time is the time required to charge the parasitic capacitance C1 formed between the source and gate of the output control transistor M1 with the current value ia supplied from the constant current circuit unit 4. Since all of the current flowing through the load 11 flows in the output control transistor M1, a transistor having a large buffer size (transistor size) is inevitably used, so that the parasitic capacitance C1 also increases. In order to control the output current value of the output control transistor M1, it is necessary to change the gate voltage of the output control transistor M1. However, since there is a large parasitic capacitance C1 between the source and the gate, it is necessary to charge and discharge the parasitic capacitance C1 with a large current in order to change the gate voltage in a short time.

  If the current ia supplied from the constant current circuit unit 4 that is the load of the driver transistor M2 is reduced in order to reduce the current consumption of the constant voltage power supply device 1, it takes much time to charge and discharge the parasitic capacitance C1. Therefore, the response speed of the output control transistor M1 with respect to the fluctuation of the output voltage Vout becomes slow. For this reason, the current control circuit unit 5 changes the current ia output from the constant current circuit unit 4 that is the load of the driver transistor M2 in accordance with the voltage value of the output voltage Vout. That is, when the output voltage Vout decreases, the output current ia of the constant current circuit unit 4 can be increased to increase the response speed when the output voltage Vout changes.

FIG. 2 is a diagram showing circuit examples of the constant current circuit unit 4 and the current control circuit unit 5 in FIG. In FIG. 2, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted here.
In FIG. 2, the constant current circuit unit 4 includes an N-channel MOS transistor (hereinafter referred to as an NMOS transistor) M3, and the current control circuit unit 5 includes an NMOS transistor M4, a PMOS transistor M5, and a resistor R3. .

  The NMOS transistor M3 of the constant current circuit unit 4 and the NMOS transistor M4 of the current control circuit unit 5 form a current mirror circuit, and the NMOS transistor M3 is connected between the drain of the driver transistor M2 and the ground voltage. A resistor R3, a PMOS transistor M5, and an NMOS transistor M4 are connected in series between the input terminal IN and the ground voltage. The gates of the NMOS transistors M3 and M4 are connected, and the connection is connected to the drain of the NMOS transistor M4. The gate of the PMOS transistor M5 is connected to the output terminal OUT.

  In such a configuration, when the output voltage Vout decreases, the gate voltage of the PMOS transistor M5 decreases and the drain current of the PMOS transistor M5 increases. Since the drain current flows through the NMOS transistor M4 forming the input side transistor of the current mirror circuit, the current becomes the drain current of the NMOS transistor M3 forming the output side transistor of the current mirror circuit, and the output current ia of the constant current circuit unit 4 become. In this way, the current supplied to the driver transistor M2 increases, the gate voltage of the output control transistor M1 can be changed in a short time, and the feedback control operation for the change in the output voltage Vout can be accelerated. it can.

  As described above, the constant voltage power supply device according to the first embodiment increases the current value of the current that charges and discharges the parasitic capacitance C1 of the output control transistor M1 in accordance with the decrease in the output voltage Vout. Part 5 was provided. As a result, the current consumption of the constant voltage power supply device can be reduced, and the response speed of the output voltage can be improved.

Second embodiment.
In the first embodiment, the current control circuit unit 5 detects the output voltage Vout and changes the load current ia for the driver transistor M2. However, the current control circuit unit 5 determines the output voltage of the error amplifier A1. The load current ia for the driver transistor M2 may be detected and changed, and such a configuration is used as the second embodiment of the present invention.
FIG. 3 is a circuit diagram showing an example of a constant voltage power supply device according to the second embodiment of the present invention. In FIG. 3, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted here, and only differences from FIG. 1 are described.

3 differs from FIG. 1 in that the current control circuit unit 5 in FIG. 1 detects the output voltage Va of the error amplifier A1, and when the output voltage Vout decreases and the detected voltage Va increases, the current control circuit unit 5 in FIG. Since the load current ia is increased, the current control circuit unit 5 in FIG. 1 is used as the current control circuit unit 21, and the constant voltage power supply device 1 in FIG. is there.
In FIG. 3, the constant voltage power supply device 20 includes a reference voltage generation circuit unit 2, a voltage dividing circuit unit 3, an output control transistor M1, an error amplifier A1, a driver transistor M2, a constant current circuit unit 4, A current control circuit unit 21 that detects the output voltage Va of the error amplifier A1 and changes the current value supplied by controlling the operation of the constant current circuit unit 4 when the detected output voltage Va increases.

The current control circuit unit 21 is operated with the voltage Vbat as a power source, the input terminal is connected to the output terminal of the error amplifier A1, and a control signal for controlling the output current is output from the output terminal to the constant current circuit unit 4. Then, the constant current circuit unit 4 supplies a current ia corresponding to the control signal to the driver transistor M2.
In such a configuration, when the state of the load 11 changes, the output current to the load 11 increases and the output voltage Vout decreases, the divided voltage Vd input to the inverting input terminal of the error amplifier A1 decreases. As a result, the output voltage Va of the error amplifier A1 rises, and the gate voltage of the driver transistor M2 rises.

  The current control circuit unit 21 changes the current ia output from the constant current circuit unit 4 that is the load of the driver transistor M2 in accordance with the voltage value of the output voltage Va of the error amplifier A1. That is, when the output voltage Vout decreases and the output voltage Va of the error amplifier A1 increases, the current control circuit unit 21 increases the output current ia of the constant current circuit unit 4 and the response speed when the output voltage Vout changes. Can be faster.

FIG. 4 is a diagram illustrating circuit examples of the error amplifier A1, the constant current circuit unit 4, and the current control circuit unit 5 in FIG. In FIG. 4, the same components as those in FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted here.
In FIG. 4, the constant current circuit unit 4 includes an NMOS transistor M3, the current control circuit unit 21 includes PMOS transistors M11 to M16, NMOS transistors M17 to M19, and a constant current source 22, and the error amplifier A1 includes a PMOS. The transistors M20 and M21 and NMOS transistors M22 to M25 are configured.

  In the current control circuit unit 21, between the input terminal IN and the ground voltage, a series circuit in which PMOS transistors M11, M12 and NMOS transistors M17, M18 are connected in series, a PMOS transistor M13, M15, an NMOS transistor M19, and A series circuit in which the NMOS transistor M25 of the error amplifier A1 is connected in series and a series circuit in which the PMOS transistors M14 and M16 and the constant current source 22 are connected in series are connected in parallel. The PMOS transistors M11, M13, and M14 form a current mirror circuit, and the PMOS transistors M12, M15, and M16 form a current mirror circuit. The NMOS transistor M18 forms a current mirror circuit with the NMOS transistor M3.

  In the PMOS transistors M11, M13, and M14, each gate is connected, the connection is connected to the drain of the PMOS transistor M14, and each source is connected to the input terminal IN. The drains of the PMOS transistors M11, M13, and M14 are connected to the sources of the PMOS transistors M12, M15, and M16. In the PMOS transistors M12, M15, and M16, the gates are connected, and the connection is connected to the drain of the PMOS transistor M16. The drains of the PMOS transistors M12 and M15 are connected to the drains of the NMOS transistors M17 and M19, and the drain of the PMOS transistor M16 is connected to the ground voltage via the constant current source 22.

  In the NMOS transistor M17, the source is connected to the drain of the NMOS transistor M18, and the gate is connected to the output terminal of the error amplifier A1. In the NMOS transistor M18, the gate is connected to the gate of the NMOS transistor M3, and the source is connected to the ground voltage. On the other hand, in the NMOS transistor M19, the gate is connected to the connection part of the gates of the PMOS transistors M11, M13, and M14, and the source is connected to the drain of the NMOS transistor M25.

  Next, in the error amplifier A1, the PMOS transistors M20 and M21 form a current mirror circuit, and the NMOS transistors M24 and M25 form a current mirror circuit. The NMOS transistors M22 and M23 form a differential pair, and the current mirror circuit of the PMOS transistors M20 and M21 forms a load for the differential pair. The current mirror circuit of the NMOS transistors M24 and M25 forms a constant current source. In the PMOS transistors M20 and M21, the gates are connected, the connection is connected to the drain of the PMOS transistor M21, and the sources are connected to the input terminal IN.

  The drains of the PMOS transistors M20 and M21 are connected to the drains of the NMOS transistors M22 and M23, respectively. The gate of the NMOS transistor M22 forms the inverting input terminal of the error amplifier A1, and the divided voltage Vd from the voltage dividing circuit unit 3 is input thereto. The gate of the NMOS transistor M23 forms the non-inverting input terminal of the error amplifier A1, and the reference voltage Vr is input thereto. The sources of the NMOS transistors M22 and M23 are connected to each other, and the connection is connected to the drain of the NMOS transistor M24. A connection part of the PMOS transistor 20 and the NMOS transistor M22 forms an output terminal of the error amplifier A1. In FIG. 4, the substrate gate of each PMOS transistor is connected to the input terminal IN, and the substrate gate of each NMOS transistor is connected to the ground voltage.

  In such a configuration, the PMOS transistors M11 and M12 are constant current loads, restrict the maximum value of the current flowing from the NMOS transistor M17, and apply a bias voltage to the drain of the NMOS transistor M17. Similarly, the PMOS transistors M13 and M15 are constant current loads that regulate the maximum value of the current flowing from the NMOS transistor M19 and apply a bias voltage to the drain of the NMOS transistor M19.

  The PMOS transistors M14 and M16 each constitute an input side transistor of the corresponding current mirror circuit, and the PMOS transistors M11, M12, M13, and M15 each constitute an output side transistor of the corresponding current mirror circuit. The series circuit of the PMOS transistors M14 and M16 is supplied with a predetermined constant current from the constant current source 22, and the PMOS transistors M13 to M16 and the NMOS transistors M19 and M25 are connected to the corresponding PMOS transistors M11 and M12 and NMOS transistor M24. The bias current is given respectively.

  When the output voltage Vout decreases and the output voltage Va of the error amplifier A1 increases, the drain current of the NMOS transistor M17 increases, and the drain current is input to the drain of the NMOS transistor M18 that forms the input side transistor of the current mirror circuit. The drain current of the NMOS transistor M3 that forms the output side transistor of the current mirror circuit increases.

FIG. 5 is a circuit diagram showing another example of the constant voltage power supply device according to the second embodiment of the present invention. In FIG. 5, the same components as those in FIG. 4 are denoted by the same reference numerals, and description thereof is omitted here, and only differences from FIG. 4 are described.
5 differs from FIG. 4 in that the drain of the PMOS transistor M11 is connected to the drain of the PMOS transistor M13, the drain of the PMOS transistor M12 is connected to the drain of the PMOS transistor M15, and the drains of the PMOS transistors M11 and M12 are connected. The rest of the operation is the same as in FIG. 4 because the voltage is stabilized.

Next, FIG. 6 is a circuit diagram showing another example of the constant voltage power supply device according to the second embodiment of the present invention. In FIG. 6, the same components as those in FIG. 4 are denoted by the same reference numerals, and description thereof is omitted here, and only differences from FIG. 4 are described.
6 is different from FIG. 4 in that the gate bias of the NMOS transistor M18 is obtained from the gate of the NMOS transistor M25 forming the current source, and other operations are the same as those in FIG. 6 shows the case of FIG. 4 as an example, but FIG. 5 shows the case of FIG.

  As described above, in the constant voltage power supply device according to the second embodiment, the current control circuit unit 21 detects the output voltage Va of the error amplifier A1, and generates the load current ia for the driver transistor M2 according to the detected voltage. I changed it. As a result, the same effect as in the first embodiment can be obtained, and the current control circuit unit 21 is completely taken into the IC, and the gate of the transistor is exposed to the outside via the output terminal OUT. Thus, the reliability of the circuit can be improved.

It is the circuit diagram which showed the example of the constant voltage power supply device in the 1st Embodiment of this invention. It is the figure which showed the circuit example of the constant current circuit part 4 and the current control circuit part 5 in FIG. It is the circuit diagram which showed the example of the constant voltage power supply device in the 2nd Embodiment of this invention. FIG. 4 is a diagram illustrating circuit examples of an error amplifier A1, a constant current circuit unit 4, and a current control circuit unit 21 in FIG. It is the circuit diagram which showed the other example of the constant voltage power supply device in the 2nd Embodiment of this invention. It is the circuit diagram which showed the other example of the constant voltage power supply device in the 2nd Embodiment of this invention. It is the circuit diagram which showed the other example of the constant voltage power supply device in the 2nd Embodiment of this invention. It is the figure which showed the example of the conventional constant voltage power supply device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,20 Constant voltage power supply device 2 Reference voltage generation circuit part 3 Voltage dividing circuit part 4 Constant current circuit part 5,21 Current control circuit part 10 DC power supply 11 Load 22 Constant current source A1 Error amplifier M1 Output control transistor M2 Driver transistor

Claims (3)

In the constant voltage power supply device that converts the voltage input from the DC power source into a predetermined DC voltage and outputs it from the output terminal,
A reference voltage generation circuit that generates and outputs a predetermined reference voltage;
A voltage dividing circuit for dividing and outputting the voltage of the output terminal;
An output control transistor that performs output control of a current supplied from the DC power supply according to an input control signal;
A driver transistor that performs drive control of the output control transistor in accordance with an input control signal;
An error amplifier for controlling the operation of the driver transistor so that the divided voltage from the voltage dividing circuit unit becomes the reference voltage;
A constant current circuit unit which supplies a constant current corresponding to an input control signal to the driver transistor and forms a load of the driver transistor;
A current control circuit unit that detects an output voltage of the error amplifier and performs operation control of the constant current circuit unit so that a constant current that changes in an analog manner according to the detected output voltage is output;
Equipped with a,
The constant voltage power supply device, wherein the current control circuit unit increases the current value of the constant current when the output voltage of the error amplifier decreases with respect to the constant current circuit unit . The constant current circuit unit is formed of a MOS transistor that outputs a current according to a voltage input to a gate, and the current control circuit unit controls a gate voltage of the MOS transistor according to an output voltage of the error amplifier. constant-voltage power supply device according to claim 1, characterized in that the. Before SL-current controller includes a constant-voltage power supply device according to claim 1 or 2, wherein a current value output from the constant current circuit portion and limits so as not to exceed a predetermined value.

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