JP2002189523A - Power source circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power source circuit capable of always supplying a fixed voltage to a load even when voltage drop corresponding to load currents is generated in wiring connecting the power source circuit to the load. SOLUTION: A voltage Vo' between output terminals 5a and 5b of a regulator 1 is voltage-divided by resistances R1 and R2, and a potential Vr2 of the voltage-dividing point is inputted to a comparator 2, and compared with a reference potential in the comparator 2. The regulator 1 controls the height of the output voltage Vo' so that a compared result 4 can be made matched. A resistance R3 is inserted between a load current path 6b connecting an output terminal 5b of the regulator 1 and an output terminal 3b of the power source circuit. Then, a fixed reference voltage Vref is added to the potential of a point 7 at the current input side of the resistance R3 as a reference so that the reference potential can be generated. When load currents Io are increased, the reference potential is increased against a detection potential Vr2 according to voltage drop at the resistance R3, and the regulator 1 increases the output voltage Vo' for matching the detection potential Vr2 with the reference potential. As a result, an output voltage Vo of the power source circuit is increased according as the load currents Io are increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit for controlling an output voltage according to a result of comparison between a reference voltage and a detection value of an output voltage.

[0002]

2. Description of the Related Art FIG. 1 shows an example of a conventional constant voltage power supply circuit of this kind. The output voltage Vo from the regulator 1 is divided by the resistors R1 and R2, and the divided voltage Vr2 is compared with a constant reference voltage Vref by the comparator 2, and the comparator 4 receives the comparison result 4 so that the two match. 1 controls the output voltage Vo. Therefore, the output voltage Vo is Vo = Vref ·
It is controlled to a constant value of (1 + R1 / R2). For example, when the reference voltage Vref is 2.5 V and R1 = R2, the output voltage Vref
o is controlled to be 5V constant.

[0003]

However, when the wiring impedance between the output terminals 3a and 3b of the power supply circuit and the load L is considerably large (for example, when the distance between the load L and the power supply circuit is considerably long), As the load current Io increases, the voltage drop in the wiring impedance becomes remarkable, and the voltage actually applied to the load L becomes the output voltage Vo of the power supply circuit.
It is much lower than that. As a result, there arises a problem that the load L does not operate normally, for example. In particular, when the output voltage Vo is originally as low as 5 V or 3.5 V (for example, in the case of a power supply circuit for a microcomputer),
The above problem is likely to occur.

Accordingly, it is an object of the present invention to provide a constant voltage capable of keeping a voltage actually applied to a load substantially constant even if a voltage drop in a wiring reaching a load increases with an increase in load current. A power supply circuit is provided.

[0005]

A power supply circuit according to the present invention comprises a detecting means for detecting a potential related to an output voltage, a comparison means for generating a reference potential, and comparing the reference potential with a detection potential from the detecting means. Means, control means for controlling the level of the output voltage according to the comparison result from the comparing means, and adjusting means for increasing the reference potential relative to the detected potential in accordance with an increase in the load current.

According to this power supply circuit, the reference potential rises relatively to the detected potential as the load current increases. Therefore, the control means receiving the result of comparing the two potentials follows the rising reference potential. In order to increase the detection potential, the output voltage is increased. Therefore, the output voltage increases with an increase in the load current, and the increase compensates for the voltage drop in the wiring connected to the load.

[0007] By appropriately setting the ratio of the relative rise of the reference potential to the increase of the load current, the voltage actually applied to the load becomes substantially constant regardless of the magnitude of the load current. Can be.

In a preferred embodiment, a voltage drop that causes a voltage drop according to the magnitude of the load current in one of a pair of load current paths coupled to an output terminal of the pair for connection with a load. An element (for example, a resistor) is inserted. Then, the detecting means generates a detection potential with reference to a potential at a current output side point of the voltage drop element,
The comparing means generates a reference potential with reference to the potential at the current input side of the voltage drop element. Therefore, as the load current increases, the reference potential is reduced by the voltage drop of the voltage drop element to the detection potential. Higher. By appropriately selecting the circuit constant of the voltage drop element, a constant voltage can always be supplied to the load.

[0009]

FIG. 2 shows a configuration of a DC constant voltage power supply circuit according to one embodiment of the present invention.

In the power supply circuit shown in FIG. 2, a regulator 1 converts a DC input voltage Vi into a DC output voltage Vo '. The output voltage Vo 'from the regulator 1 is divided by the series circuit of the voltage dividing resistors R1 and R2, and the potential at the voltage dividing point (that is, the detection potential related to the output voltage Vo of the power supply circuit) Vr2 is obtained by the comparator 2 Is input to The comparator 2 internally generates a constant reference voltage Vref using, for example, a Zener diode or the like, and compares the potential on the reference voltage Vref side (that is, the reference potential) with the detection potential Vr2. In response to the comparison result 4, the regulator 1 controls the output voltage Vo ′ so that the two potentials match.

As shown in the figure, the above-mentioned voltage dividing resistors R1, R
2 are connected to the output terminals 5a and 5b of the regulator 1.
Therefore, the voltage at both ends of the lower resistor R2 that has a ground potential at the origin corresponds to the detection potential Vr2. Output terminals 5a, 5b of the regulator 1
And the output terminals 3a and 3b of the power supply circuit to be connected to the load L are connected by a pair of load current paths 6a and 6b for circulating the load current Io. The comparator 2 is connected to the lower load current path 6a of the pair of load current paths 6a and 6b from which the load current Io is fed back.
It is connected to point 7 on b. Then, the comparator 2 generates a constant reference voltage Vref on the potential at the point 7 using the potential at the point 7 as an origin, for example, using a Zener diode connected to the point 7. . Therefore, the reference potential to be compared with the detection potential Vr2 is a level obtained by adding a constant reference voltage Vref to the potential at the point 7. Then, a point 7 for determining the reference potential in the lower load current path 6b
A resistor R3 is inserted between the power supply 5 and a point 5b at the ground potential (output terminal of the regulator 1).
Therefore, in this power supply circuit, it can be said that the detection potential Vr2 is generated based on the current output point 5b of the resistor R3, and the reference potential is generated based on the current input point 7 of the resistor R3.

In the above configuration, when the load current Io flows, a voltage drop Io.R3 occurs at the resistor R3, and the potential at the point 7 that determines the reference potential becomes higher than the ground potential by the amount of the voltage drop. Therefore, when the load current Io increases, the reference potential and the detection potential compared by the comparator 2 are compared.
The relationship with Vr2 changes so that the reference potential is relatively higher (that is, the detection potential Vr2 is relatively lower). The regulator 1 receiving the comparison result 4 from the comparator 2 increases the load current Io,
The output voltage Vo 'is increased so that the detection potential Vr2 is also increased following the rising reference potential. As a result, the output voltage V appearing at the output terminals 3a and 3b of this power supply circuit
o also increases with an increase in the load current Io (of course, the voltage drop at the resistor R3 also increases, but the output voltage Vo 'of the regulator 1 increases more than that. As a result, the output voltage Vo rises).

This is quantitatively described as follows.

The reference potential is obtained by adding the voltage drop at the resistor R3 to the reference voltage Vref, and is "Vref + Io.R3". The regulator 1 uses the reference potential “Vref + Io · R
3 ”and the detection potential Vr2 are controlled so that Vr2 = Vref + Io · R3 (1) is always established.

When the detected potential Vr2 is represented by using the output voltage Vo of this power supply circuit, the following equation is obtained: Vr2 = (Vo + Io · R3) × R2 / (R1 + R2) (2)

Then, if the right sides of the above equations (1) and (2) are assumed to be equal to each other and the equation is solved for the output voltage Vo, then Vo = Vref （(1 + R1 / R2) + Io ・ R3 ・ R1 / R2 ... ... (3) Incidentally, in the conventional circuit shown in FIG. 1, Vo = Vref. (1 + R1 / R2).

As can be seen from the equation (3), the output voltage Vo of the power supply circuit according to the present embodiment increases linearly with an increase in the load current Io. The rate of increase is determined by the constants R3, R1 / R2. Since R1 / R2 is a constant for determining the basic relationship between the output voltage Vo and the reference voltage Vref, in order to determine the rate of increase of the output voltage Vo in accordance with the load current Io, in particular, the resistance value of the resistor R3
R3 is important. By appropriately selecting the resistance value R3 according to the magnitude of the wiring impedance, the voltage actually applied to the load L can be controlled to be constant regardless of the load current Io.

FIG. 3 is a circuit diagram of a more specific example of the constant voltage power supply circuit shown in FIG.

In this power supply circuit, a DC-CD converter of a chopper type is used as the regulator 1. That is, the controller 8 controls the duty of the switching element Q in accordance with the comparison result from the comparator 2 to adjust the output voltage Vo ′. On the output side of the switching element Q, there is a current / voltage smoothing circuit including a DC reactor L, a smoothing capacitor C, a flywheel diode D, and the like.

FIG. 4 shows a power supply circuit according to another embodiment.

In this power supply circuit, a resistor R3 for causing a voltage drop according to the load current Io is inserted in the upper load current path 6a in which the load current Io flows toward the load L. A series circuit of voltage dividing resistors R1 and R2 is connected between points 3a and 3b on the current output side of the resistor R3 (that is, the output terminal of the power supply circuit), and the potential Vr2 at the voltage dividing point is compared with a comparator. 10 is input. The comparator 10 uses a Zener diode or the like connected to a point on the current input side of the resistor R3 (i.e., the upper output terminal of the regulator 1) 5a.
(This is equal to the output voltage Vo ′ of the regulator 1), and a constant reference voltage −Vref is generated thereunder. Therefore, the reference potential to be compared with the divided potential Vr2 is a potential obtained by adding the reference voltage −Vref to the output voltage Vo ′ of the regulator 1. Receiving the comparison result 11 from the comparator 10, the regulator 1 adjusts its output voltage Vo 'so that the comparison result becomes coincident.

In the power supply circuit of FIG. 4, the following characteristic is obtained: Vo = Vrefref (1 + R2 / R1) + Io ・ R3 ・ (1 + R2 / R1) (4) Rises linearly.

The embodiment described above is an example for explaining the present invention, and the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the invention. . For example, in the above embodiment, as the means for changing the relationship between the two potentials to be compared according to the load current Io, the resistor R3 inserted in one of the load current paths is used. However, the present invention is not limited to this. Not something. Therefore, without departing from the gist of the present invention, it is possible to use a circuit having various other configurations that raises the reference potential with respect to the detected potential in accordance with an increase in the load current.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a conventional constant voltage power supply circuit.

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

FIG. 3 is a circuit diagram showing a more specific configuration example of the constant voltage power supply circuit of FIG. 2;

FIG. 4 is a circuit diagram showing a constant voltage power supply circuit according to another embodiment of the present invention.

[Explanation of symbols]

 1 Regulator 2, 10 Comparator 4, 11 Comparison result R1, R2, R3 Resistance L Load Vo Output voltage Io Load current Vref Reference voltage Vr2 Detection potential

Claims (3)

[Claims] A detecting means for detecting a potential related to an output voltage; a comparing means for generating a reference potential; comparing the reference potential with a detected potential from the detecting means; and a comparison result from the comparing means. A power supply circuit comprising: control means for controlling the height of the output voltage in response to the control signal; and adjusting means for increasing the reference potential relative to the detection potential as the load current increases. 2. A pair of output terminals for connection to a load, and a pair of load current paths through which the load current flows, coupled to the output terminals of the pair, wherein the adjusting means includes one load current. A voltage drop element that is inserted into the path and generates a voltage drop according to the magnitude of the load current flowing therethrough, wherein the detection unit detects the potential based on a potential at a current output side point of the voltage drop element. 2. The comparison unit generates the reference potential with reference to a potential at a current input side point of the voltage drop element.
Power supply circuit as described. 3. In the adjusting means, a ratio of a relative increase in the reference potential to an increase in the load current is such that a voltage actually applied to the load is substantially constant regardless of the magnitude of the load current. 2. The power supply circuit according to claim 1, wherein the power supply circuit is set to such a value.