JP2012073799A - Regulator circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a regulator circuit which has a current control circuit connected to an opposite phase output node of a differential amplifier circuit and is capable of suppressing lowering of DC gain due to lowering of impedance in the opposite phase output node.SOLUTION: A circuit shown in Fig. 2 is the regulator circuit having the current control circuit connected to the opposite phase output node of the differential amplifier circuit. The current control circuit includes: a second transistor MP2 as a current detection transistor supplying a current proportional to a current flowing through a first transistor MP1, a first constant current source MN1 connected to a drain end of the second transistor MP2; and a current mirror having an input side connected to a shunt node between the drain end of the second transistor MP2 and the first constant current source MN1 and an output side connected to the opposite phase output node of the differential amplifier circuit. The current mirror is composed of the transistor MN2 on the input side and the transistor MN3 on the output side.

Description

  The present invention relates to a regulator circuit that converts an input voltage into a desired output voltage.

  Conventionally, in a regulator circuit that converts an input voltage into a desired output voltage by controlling the gate bias VGATE of the output transistor, the gate bias is controlled based on the output voltage and the current flowing through the output transistor as shown in FIG. A regulator circuit having a current limiting circuit is known (see Patent Document 1).

  The regulator circuit shown in FIG. 1 is a regulator circuit that converts an input voltage into a desired output voltage by controlling the gate bias VGATE of the output transistor MP1, and includes a predetermined reference voltage VREF input to the positive phase input node. A differential amplification circuit that differentially amplifies a voltage value VFB corresponding to the output voltage input to the negative phase input node and outputs a gate bias VGATE from the positive phase output node; and a reverse of the differential amplification circuit And a current control circuit connected to the phase output node. This current control circuit has a current detection transistor MP2 that supplies a current proportional to the current flowing through the output transistor MP1, an input side connected to the drain terminal of the current detection transistor MP2, and an output side connected to the negative phase output node of the differential amplifier circuit. Current mirror. The current mirror includes an input-side transistor MN2 and an output-side transistor MN3.

  Next, the operation of the circuit shown in FIG. 1 will be described.

  In the steady state of the regulator circuit shown in FIG. 1, the current IP1 flowing through the output transistor MP1 increases due to load fluctuations, and the current IP2 flowing through the current detection transistor MP2 increases in proportion thereto. When the current IP2 increases, the current IN3 also increases through the current mirror. When the current IN3 increases, the potential of the negative phase output node of the differential amplifier circuit decreases, and the current IP5 increases. When the current IP5 increases, the gate bias VGATE increases and the current IP1 flowing through the output transistor MP1 decreases, so that it is possible to suppress an excessive increase in the current IP1 flowing through the output transistor MP1.

JP 2007-233657 A

  However, in the regulator circuit shown in FIG. 1, the current IN3 always flows as long as the current IP1 flows through the output transistor MP1 even at the start-up or in the steady state. When the current IN3 always flows, the impedance of the negative phase output node of the differential amplifier circuit is lowered, and the DC gain as the regulator circuit is greatly lowered. As a result, the output voltage accuracy deteriorates.

  Further, at the start-up time when the difference between the input voltage and the output voltage is large, a large current flows through the output transistor MP1, so that the impedance of the negative-phase output node is significantly reduced, the DC gain is greatly reduced, and the steady state is reached. Takes too much time.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a regulator circuit having a current control circuit connected to a negative-phase output node of a differential amplifier circuit. An object of the present invention is to provide a regulator circuit capable of suppressing a decrease in DC gain due to a decrease in impedance.

  As a result of intensive studies to solve the above problems, the present inventor is a regulator circuit that converts an input voltage into a desired output voltage by controlling the gate bias of the first transistor, and includes a positive-phase input node. A differential amplifier circuit that differentially amplifies a predetermined reference voltage input and a voltage value corresponding to the output voltage input to a negative phase input node, and outputs the gate bias from a positive phase output node; A current control circuit connected to a negative phase output node of the differential amplifier circuit, wherein the current control circuit includes a second transistor for flowing a current proportional to a current flowing in the first transistor, and the second transistor A first constant current source connected to the drain end of the first transistor, and an input side connected to a shunt node between the drain end of the second transistor and the first constant current source; Found that to solve the above problems by the regulator circuit; and a current mirror side is connected to the negative-phase output node of said differential amplifier circuit, and completed the present invention.

  According to the present invention, in a regulator circuit having a current limiting circuit connected to the negative phase output node of the differential amplifier circuit, it is easy to reduce the impedance of the negative phase output node and the DC gain. It is possible to suppress.

It is a figure which shows the conventional regulator circuit. It is a figure which shows the 1st example of the regulator circuit of this invention which has a current limiting circuit. It is a figure which shows the example of the conventional regulator circuit which has a starting completion detection circuit. FIG. 4 is a diagram illustrating a comparative example in which the activation completion detection circuit of FIG. 3 is directly applied to the regulator circuit of FIG. 2. It is a figure which shows the 2nd example of the regulator circuit of this invention which has a starting completion detection circuit.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<First example>
The circuit shown in FIG. 2 is a regulator circuit that converts an input voltage into a desired output voltage by controlling the gate bias VGATE of the first transistor MP1 as an output transistor, and is a predetermined circuit that is input to a positive phase input node. Differential amplification circuit that differentially amplifies the reference voltage VREF of the current and the voltage value VFB corresponding to the output voltage input to the negative phase input node and outputs the gate bias VGATE from the positive phase output node, and the difference And a current control circuit connected to the negative phase output node of the dynamic amplifier circuit. In FIG. 2, a voltage value VFB corresponding to the output voltage is a voltage value obtained by dividing the output voltage VOUT by the resistors R1 and R2. According to the present invention, since the DC gain is suppressed from being lowered, it is ensured that high phase compensation is ensured as compared with the regulator circuit of the prior art as shown in FIG. To preferred. In the case of using a resistance-divided voltage value, it is preferable to connect the capacitive element C2 in parallel to the resistor R1 closer to the output voltage VOUT in order to ensure phase compensation.

  The current control circuit includes a second transistor MP2 serving as a current detection transistor that supplies a current proportional to a current flowing through the first transistor MP1, and a first constant current source MN1 connected to the drain terminal of the second transistor MP2. And a current mirror whose input side is connected to a shunt node between the drain end of the second transistor MP2 and the first constant current source MN1, and whose output side is connected to a negative phase output node of the differential amplifier circuit. . The current mirror includes an input-side transistor MN2 and an output-side transistor MN3.

  Next, the operation of the circuit shown in FIG. 2 will be described.

  When the current IP2 flowing through the second transistor MP2 is less than or equal to the saturation operation current value IN1 of the first constant current source MN1 (when IP2 ≦ IN1), no current flows through the transistor MN2 on the input side of the current mirror, and the output No current flows through the side transistor MN3. Therefore, in the state of IP2 <IN1, the potential of the negative phase output node of the differential amplifier circuit is not affected by the current limiting circuit, and the impedance and the DC gain do not decrease. In the state of IP2 <IN1, the gate bias VGATE of the first transistor MP1 is controlled so that the voltage signal VFB obtained by dividing the output voltage by the resistors R1 and R2 matches the reference voltage VREF.

  When the current IP2 flowing through the second transistor MP2 is larger than the current IN1 flowing through the first constant current source (when IP2> IN1), a current of IN2 = IP2-IN1 flows, and a current flows through the output transistor MN3. A current IN3 corresponding to IN2 flows.

  When the current IN3 flows, the potential of the negative phase output node of the differential amplifier circuit decreases, the currents IP4 and IP5 increase, and the gate bias VGATE increases, so that the current flowing through the first transistor MP1 is suppressed.

  As described above, according to the circuit of FIG. 2, when the current IP2 flowing through the second transistor MP2 proportional to the current IP1 flowing through the first transistor MP1 is smaller than the current IN1, that is, flowing through the first transistor MP1. When the current limit of the current IP1 is not performed, the impedance of the negative phase output node and the DC gain do not decrease, and the current IP2 flowing through the second transistor MP2 proportional to the current IP1 flowing through the first transistor MP1 The current limiting circuit operates only when the current is larger than IN1, that is, when the current IP1 flowing through the first transistor is limited, and a desired current can be limited.

<Second example>
(Conventional startup completion detection circuit)
Conventionally, as shown in FIG. 3, a transistor MP3 whose gate is connected to the negative phase output node of the differential amplifier circuit, a constant current source connected to the drain terminal of the transistor MP3, and a transistor MP3 and a constant current source There is known a regulator circuit including a start completion detection circuit having a start completion detection signal terminal present at a node between them. This activation completion detection circuit utilizes the fact that the activation completion detection signal VOK becomes HIGH (so-called current comparison) when the current value of the current IP3 flowing through the transistor MP3 becomes larger than the constant current value IN5. . When the transistor MP3 is driven by VPBIAS when the output voltage reaches a desired value, the output voltage reaches the desired value by determining the constant current value IN5 so that the current IP3 becomes larger than the constant current value IN5. And detecting that the startup is complete.

(Problems when the conventional startup completion detection circuit is incorporated as is)
However, as shown in FIG. 4, when the conventional start completion detection signal of FIG. 3 is incorporated in the regulator circuit of the present invention shown in FIG. 2, if the current limiting circuit operates before the output voltage reaches a desired value, Since the potential of the negative phase output node of the differential amplifier circuit decreases and the current IP3 increases, the activation completion detection signal VOK becomes HIGH before the output voltage reaches a desired value, and erroneous detection is performed.

(Description of FIG. 5)
Therefore, as in the circuit according to the second example of the present invention shown in FIG. 5, the third transistor MP3 whose gate is connected to the negative phase output node of the differential amplifier circuit, and the drain terminal of the third transistor MP3. The connected second constant current source MN5, the activation completion detection signal terminal present at the node between the third transistor MP3 and the second constant current source MN5, the drain being the activation completion detection signal terminal and the second By incorporating a start-up completion detection circuit having a fourth transistor MN4 connected to a node between the constant current source MN5 and having a gate connected to the shunt node into the regulator circuit shown in FIG. It is possible to prevent the erroneous detection in which the activation completion detection signal VOK becomes HIGH before reaching the value of. Although not particularly limited, it is possible to more accurately suppress the startup completion detection signal VOK from becoming HIGH before the output voltage reaches a desired value due to variations in device performance of the transistors MP3, MN4, and MN5 due to process variations. Therefore, it is preferable that the resistor R3 is provided between the third transistor MP3 and the activation completion detection signal terminal.

  This will be described for the operation of the regulator circuit when the current limiting circuit operates before the output voltage reaches a desired value in the circuit of FIG.

  When IP2> IN1, the current IN3 flows through the transistor MN3 on the output side of the current mirror as described above. Corresponding to the current value of the current IN3, the potential of the negative phase output node of the differential amplifier circuit decreases, and the current IP3 increases. At this time, since the gate bias of the fourth transistor MN4 is the same as the gate bias of the output-side transistor MN3, the current IN4 flowing through the fourth transistor MN4 flows in proportion to the current IN3. If transistors MN4, MN5, and MP3 in which currents IN3 to IN5 at this time satisfy IN4 + IN5> IP3 are used, even if the current limiting circuit operates before the output voltage reaches a desired value, start-up completion detection signal VOK is It becomes possible to prevent false detection without becoming HIGH.

MN1 First constant current source MN2 Input side transistor constituting the current mirror MN3 Output side transistor constituting the current mirror MN4 Fourth transistor MN5 Second constant current source MP1 First transistor MP2 Second transistor MP3 Third transistor R3 resistance element

Claims (5)

A regulator circuit that converts an input voltage into a desired output voltage by controlling a gate bias of a first transistor,
A difference in which a predetermined reference voltage input to the positive phase input node and a voltage value corresponding to the output voltage input to the negative phase input node are differentially amplified and the gate bias is output from the positive phase output node. A dynamic amplification circuit;
A current control circuit connected to the negative phase output node of the differential amplifier circuit,
The current control circuit is
A second transistor for passing a current proportional to the current flowing in the first transistor;
A first constant current source connected to a drain terminal of the second transistor;
An input side connected to a shunt node between the drain end of the second transistor and the first constant current source, and an output side having a current mirror connected to a negative phase output node of the differential amplifier circuit; Regulator circuit characterized by. A third transistor having a gate connected to a negative phase output node of the differential amplifier circuit;
A second constant current source connected to the drain end of the third transistor;
An activation completion detection signal terminal present at a node between the third transistor and the second constant current source;
And a start completion detection circuit having a drain connected to a node between the start completion detection signal terminal and the second constant current source and a gate connected to the shunt node. The regulator circuit according to claim 1.   A resistor element is provided between the third transistor and the second constant current source, and the activation completion detection signal terminal is present at a node between one end of the resistor element and the second constant current source. The regulator circuit according to claim 2.   The regulator circuit according to claim 1, wherein gates of the first transistor and the second transistor are connected to a positive phase output node of the differential amplifier circuit.   The regulator circuit according to claim 1, wherein sources of the first to third transistors are connected to an input voltage.

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