JP2005011133A - Voltage regulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage regulator capable of sufficiently suppressing the variation of an output voltage caused by a leak current generated in an output transistor even with a simple configuration. <P>SOLUTION: A leak current absorption circuit 41 is disposed between an output terminal Vout and ground. The leak current absorption circuit 41 includes a 1st resistor 45 whose one end is connected to the output terminal Vout, 2nd and 3rd resistors 46, 47 which are interconnected in series between the output terminal Vout and the ground and a leak current absorbing transistor 48 whose drain is connected to the other terminal of the 1st resistor 45, source is grounded and gate is connected to a node between the 2nd resistor 46 and the 3rd resistor 47. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a voltage regulator, and more particularly to a technique for suppressing fluctuations in output voltage due to an off-leak current of an output transistor.
[0002]
[Prior art]
The basic configuration of the voltage regulator is as shown in FIG. In other words, the voltage regulator is connected between the output transistor Q11 connected between the first power supply terminal 11 and the output terminal 12, and between the output terminal 12 and the second power supply terminal (ground terminal) 13, and output. A pair of series-connected resistors R11 and R12 that divide the voltage at the terminal 12 (output voltage VO) and the input voltage VI at the input terminal 14 and the voltage divided by the resistors R11 and R12 are compared to output transistor. And an operational amplifier OP11 for controlling Q11.
[0003]
By applying a reference voltage (= VI) to the input terminal 14 of the voltage regulator of FIG. 1, the output voltage VO output to the output terminal 2 is ideally VO = VI (R11 / R12 + 1) Stabilized regardless of voltage.
[0004]
However, actually, a leakage current may be generated in the output transistor Q11, and the output voltage varies. Therefore, a voltage regulator is conventionally known that is configured to absorb a leak current generated in the output transistor and suppress fluctuations in the output voltage.
[0005]
A conventional voltage regulator with a countermeasure against leakage current is configured as shown in FIG. 2 (see, for example, Patent Document 1).
[0006]
More specifically, the voltage regulator of FIG. 2 includes a first transistor Q21 having a source and a drain connected to the first power supply terminal 21 and the output terminal 22, respectively, and between the output terminal 22 and the second power supply terminal 23. First, second, and third resistors R21, R22, and R23 connected in series, a second transistor Q22 having a drain and a source connected to the output terminal 22 and the second power supply terminal, respectively, and an inverting input terminal Is connected to the input terminal 23, the non-inverting input terminal is connected to the connection point between the first resistor R21 and the second resistor R22, and the output terminal is connected to the gate of the first transistor Q21. The operational amplifier OP1 and the inverting input terminal are connected to the input terminal 23, the non-inverting input terminal is connected to the connection point between the second resistor R22 and the third resistor R23, and Output terminals of and a second operational amplifier OP2 connected to the gate of the first transistor Q21.
[0007]
In this voltage regulator, the first operational amplifier OP21, like the operational amplifier of FIG. 1, stabilizes the output voltage, that is, the first transistor Q1 so that VO = VI (R21 / (R22 + R23) +1). To control. At this time, if a leak current flows even though the first transistor Q21 is off, the output voltage VO at the output terminal 22 rises. The second operational amplifier OP22 turns on the second transistor Q22 when the voltage at the connection point between the second resistor R22 and the third resistor R23 increases and exceeds the input voltage VI as the output voltage VO increases. Absorbs leakage current. In this way, in the voltage regulator of FIG. 2, even if a leakage current occurs in the first transistor that is an output transistor, it can be absorbed and suppressed from changing the output voltage.
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 6-138916 (particularly FIG. 1)
[0009]
[Problems to be solved by the invention]
The conventional voltage regulator uses an operational amplifier in order to suppress fluctuations in the output voltage due to the leakage current of the output transistor, and has a problem that the configuration is complicated.
[0010]
Therefore, an object of the present invention is to provide a voltage regulator that can sufficiently suppress fluctuations in output voltage due to leakage current generated in an output transistor, while having a simpler configuration.
[0011]
[Means for Solving the Problems]
According to the present invention, the output transistor (31) connected between the power supply terminal (VDD) and the output terminal (Vout), and the output voltage supplied from the power supply terminal to the output terminal via the output transistor A voltage dividing circuit (32) for generating a detection voltage by dividing the voltage and an operational amplifier (36) for controlling the output transistor based on a reference voltage and the detection voltage and stabilizing the output voltage. In the voltage regulator, it is possible to obtain a voltage regulator characterized by including a leakage current absorption circuit (41) that operates independently from the reference voltage and absorbs the leakage current of the output transistor.
[0012]
Specifically, in the voltage regulator, the leakage current absorption circuit (41A) includes a first resistor (45) connected to the output terminal and a leakage current control connected between the resistor and the ground. Transistor (48), and the second and third resistors (46) connected in series between the output terminal and the ground, and connected to the control terminal of the leakage current control transistor at the connection point. 47).
[0013]
Alternatively, in the voltage regulator, the leakage current absorption circuit (41B) includes a resistor (61) connected to the output terminal and a leakage current control transistor (62) connected between the resistor and the ground. The inverted signal obtained by inverting the on / off signal supplied to the operational amplifier is supplied to the control terminal of the transistor.
[0014]
In addition, the code | symbol in the said parenthesis is attached | subjected in order to make an understanding of this invention easy, Comprising: This invention is not limited at all.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0016]
FIG. 3 shows a schematic configuration of a voltage regulator 30 according to an embodiment of the present invention.
[0017]
The illustrated voltage regulator 30 divides an output transistor 31 whose source and drain are connected to a power supply terminal VDD and an output terminal Vout, respectively, and an output voltage supplied to the output terminal Vout via the output transistor 31 to generate a detection voltage. A voltage dividing circuit 32, a phase correcting capacitor 33, a constant current source 34 and a reference voltage source 35 for generating a reference voltage, and an operational amplifier 36 that controls the output transistor 31 by comparing the detected voltage with the reference voltage. Leakage current connected in parallel with the current limiting circuit 37, the NOT circuit pair 38, the separating transistor 39, the input resistor 40, and the voltage dividing circuit 32 (ie, between the output terminal Vout and the ground). And an absorption circuit 41.
[0018]
In this voltage regulator 30, when the high level “H” is input to the ON / OFF terminal CE, the operational amplifier 36 operates. The operational amplifier 36 has a reference voltage generated by the constant current source 34 and the reference voltage source 35 at its inverting input terminal and a detection voltage obtained by dividing the output voltage by the voltage dividing circuit 32 at its non-inverting input terminal. . Therefore, when the high level “H” is input to the ON / OFF terminal CE, the operational amplifier 36 controls the output transistor 31 so that the divided voltage matches the reference voltage. That is, the operational amplifier 36 turns on the output transistor 31 to increase the output voltage when the divided voltage is lower than the reference voltage, and turns off the output transistor 31 when the divided voltage is equal to or higher than the reference voltage. To reduce the output voltage.
[0019]
On the other hand, when the low level “L” is input to the ON / OFF terminal CE, the operational amplifier 36 stops its operation. At this time, the gate of the output transistor 31 is maintained at a high level by the action of the current limiting circuit 37, and the output transistor 31 remains off.
[0020]
The leak current absorption circuit 41 absorbs a leak current flowing through the output transistor 31 when the output transistor 31 is off. The leak current flowing through the output transistor 31 is likely to occur when a low level is supplied to the ON / OFF terminal CE, or at a light load and at a high temperature (for example, 85 ° C. or more).
[0021]
For example, the leakage current absorption circuit 41 is configured as shown in FIG. That is, the leakage current absorption circuit 41 includes a first resistor 45 having one end connected to the output terminal Vout, and second and third resistors 46 connected in series between the output terminal Vout and the ground. 47, a leakage current absorption transistor 48 having a drain connected to the other end of the first resistor 45, a source grounded, and a gate connected to a connection point between the second resistor 46 and the third resistor 47 have.
[0022]
In this leakage current absorption circuit 41, when the divided voltage obtained by dividing the output voltage supplied to the output terminal Vout by the second resistor 46 and the third resistor 47 becomes a predetermined value or more, the leakage current absorption circuit 41 The transistor 48 is turned on to absorb the leak current generated in the output transistor 31. Thereby, it is possible to prevent an increase in output voltage due to a leakage current when the output transistor 31 is off. Moreover, no operational amplifier is required to control the leakage current absorbing transistor 48.
[0023]
In the leakage current absorption circuit 41 of FIG. 4, the characteristic (threshold value) of the leakage current absorption transistor 48 may change due to a change in ambient temperature. That is, the leakage current absorption circuit 41 may not be able to stabilize the output voltage due to a change in ambient temperature.
[0024]
Therefore, in order to compensate for the temperature characteristics of the leakage current absorbing transistor 48, a temperature compensating transistor 51 connected in parallel with the first resistor 45 may be provided as shown in FIG. In the leakage current absorption circuit 41A, the threshold value of the leakage current absorption transistor 48 increases with the ambient temperature change (for example, 0.6V → 1.1V), and the output voltage becomes a predetermined value or more. Regardless, when the leakage current absorption transistor 48 is not turned on, the temperature compensation transistor 51 is turned on to increase the source-drain voltage of the leakage current absorption transistor 48, and thereby the leakage current absorption transistor 48. Turn on. As a result, the leakage current absorption circuit 41A can stabilize the output voltage with almost no influence of the ambient temperature change.
[0025]
Further, the leakage current absorption circuit 41 may be configured as shown in FIG. The leakage current absorption circuit 41B has a resistor 61 having one end connected to the output terminal Vout, a drain connected to the other end of the resistor 61, a source grounded, and a gate connected to two NOT circuits of the NOT circuit pair 38. And a leakage current absorbing transistor 62 connected to the point.
[0026]
In the leakage current absorption circuit 41B of FIG. 6, when the input to the ON / OFF terminal CE becomes low level, a high level that is an inverted signal thereof is given to the gate of the leakage current absorption transistor 62. As a result, the leakage current absorption transistor 62 is turned on, and the leakage current flowing through the output transistor 31 is absorbed.
[0027]
As described above, according to the voltage regulator according to the present embodiment, the leakage current of the output transistor can be absorbed and a stable output voltage can be obtained with a simple configuration.
[0028]
While the present invention has been described with reference to one embodiment, the present invention is not limited to the above embodiment.
[0029]
For example, although the case where a p-channel MOS transistor is used as the output transistor 31 has been described in the above embodiment, the output transistor may be an n-channel MOS transistor, a PNP or an NPN bipolar transistor. The connection relationship between the output transistor and the operational amplifier in these cases is shown in FIGS. 7 (a), (b) and (c), respectively.
[0030]
As for the leakage current absorbing transistor, an n-channel MOS transistor is used in the above embodiment, but another type of transistor can be used.
[0031]
【The invention's effect】
According to the present invention, the leakage current absorption circuit that operates independently from the reference voltage is provided so as to absorb the leakage current generated in the output transistor, so that the fluctuation of the output voltage can be sufficiently suppressed even with a simple configuration. Can be suppressed.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a basic configuration of a conventional voltage regulator.
FIG. 2 is a circuit diagram showing a configuration of a voltage regulator with a conventional countermeasure against leakage current.
FIG. 3 is a circuit diagram showing a configuration of a voltage regulator according to an embodiment of the present invention.
4 is a circuit diagram for explaining a configuration example of a leakage current absorption circuit used in the voltage regulator of FIG. 3;
5 is a circuit diagram for explaining a modification of the voltage regulator of FIG. 4; FIG.
6 is a circuit diagram for explaining another configuration example of a leakage current absorption circuit used in the voltage regulator of FIG. 3;
7A, 7B, and 7C are circuit diagrams showing connection relationships between various transistors that can be used as output transistors in the voltage regulator of FIG. 3 and operational amplifiers.
[Explanation of symbols]
30 voltage regulator 31 output transistor 32 voltage dividing circuit 33 output capacitor 34 constant current source 35 reference voltage source 36 operational amplifier 37 current limiting circuit 38 NOT circuit pair 39 separating transistor 40 input resistor 41 leakage current absorption circuit 45 first resistor 46 first resistor 46 2 resistor 47 third resistor 48 leak current absorbing transistor 51 temperature compensating transistor 61 resistor 62 leak current absorbing transistor

Claims (4)

An output transistor connected between the power supply terminal and the output terminal; and a voltage dividing circuit for dividing the output voltage supplied from the power supply terminal to the output terminal via the output transistor to generate a detection voltage; In a voltage regulator including an operational amplifier that controls the output transistor based on a reference voltage and the detection voltage and stabilizes the output voltage,
A voltage regulator comprising a leakage current absorption circuit that operates independently of the reference voltage and absorbs a leakage current of the output transistor. The voltage regulator according to claim 1,
The leakage current absorption circuit includes a first resistor connected to the output terminal, a leakage current control transistor connected between the first resistor and the ground, and between the output terminal and the ground. A voltage regulator comprising: a second resistor and a third resistor connected in series to each other and having a connection point connected to a control terminal of the leakage current control transistor. The voltage regulator according to claim 2,
2. A voltage regulator comprising: a temperature compensation transistor for compensating a temperature characteristic of the leakage current control transistor in parallel with the first resistor. The voltage regulator according to claim 1,
The leakage current absorption circuit includes a resistor connected to the output terminal, and a leakage current control transistor connected between the resistor and the ground,
A voltage regulator, wherein an inverted signal obtained by inverting an on / off signal supplied to the operational amplifier is supplied to a control terminal of the transistor.

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