JP2000184703A - Power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reliably perform overvoltage protection operation by varying a reference value for detecting overvoltage corresponding to the setting of an output voltage. SOLUTION: When setting a reference value Vref2 of an overvoltage detection part by a variable resistor or the like being provided separately from the setting operation of a variable resistor VR1 of an output voltage detection part 8, a user needs to set an output voltage and the reference value Vref2 for detecting overvoltage, so that the setting operation becomes complex and hence an erroneous operation may occur easily. However, it is convenient that the output voltage and the reference value Vref2 for detecting overvoltage can be simultaneously set simply by operating a variable resistor Vr1. Since the reference value for detecting overvoltage is varied corresponding to the setting of the output voltage, the overvoltage detection reference value also varies when the output voltage is set to a low value, thus performing overvoltage protection operation according to a load to be connected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for controlling an output voltage to a constant voltage value and performing an overvoltage protection operation when the output voltage is an overvoltage.

[0002]

2. Description of the Related Art A conventional power supply of this type will be described with reference to FIG. 2 is an input smoothing unit for rectifying and smoothing the AC input, 4 is a converter unit which includes a transformer and a switching element and converts the input to a predetermined output, 6 is an output rectifying and smoothing unit for rectifying and smoothing the output of the converter unit, and 8 is a resistor. R1, a variable resistor VR1 and a resistor R2 connected in series to form an output voltage Vo.
Is a comparison feedback unit that compares the detection value Vd of the output voltage Vo from the output voltage detection unit 8 with the reference value Vref, and feeds back a result of the comparison. Reference numeral 12 denotes a Zener diode Z1, The output voltage Vo is composed of a coupler PC1 and a resistor R5.
This is an overvoltage detection unit that detects an overvoltage of the power supply. Reference numeral 14 denotes a detection value Vd in response to the output of the comparison feedback unit 10.
Is controlled so that the output voltage Vo becomes constant by controlling the operation of the switching element of the converter unit 4 so that the output voltage Vo becomes equal to the reference value Vref, and when the overvoltage detection is input from the overvoltage detection unit 12, the converter unit 4 Is a control unit for controlling the stop of the operation and shutting down the output. In addition,
Since the detailed operation of such a power supply device is well known, its description is omitted.

[0003]

In the case of the power supply having the above configuration, the variable resistor VR1 of the output voltage detector 8 is used.
The voltage at the connection point a, that is, the variable range of the detection value Vd, can be used to change the output voltage Vo to a constant value. However, the overvoltage is determined by the zener voltage Vz of the zener diode Z1. Have been. That is, in the conventional power supply device, the output voltage Vo can be arbitrarily set within the variable range, but the output voltage for the overvoltage protection operation is a fixed value of the zener voltage Vz. Therefore, for example, the variable range of the output voltage Vo is 4.5 V to 5.5.
The following problem is pointed out when the power supply device is set to V and the overvoltage Zener voltage Vz is set to be constant at 6.0 V.

That is, depending on the load connected to the output, the output voltage Vo is set to 4.5 V, which is the lower limit of the variable range, in view of the voltage specification of the load, while the output voltage Vo is set in accordance with the voltage specification of this load. When the voltage value of the output voltage is 5.5 V, which is smaller than the Zener voltage Vz of 6.0 V, in this power supply device, even if the output voltage becomes 5.5 V which is an overvoltage for this load, the overvoltage There is a problem that the protection operation is not performed, and the protection operation cannot be performed for a load having such a specification.

In order to make the above-mentioned power supply device usable for a load having such a specification, a circuit for externally performing an overvoltage protection operation with 5.5V as an overvoltage corresponding to the load connected thereto is additionally provided. This is disadvantageous in terms of cost, and there is a problem that the size of the entire apparatus is also increased.

Further, due to the specifications of another load, the output voltage Vo
Is set to 5.5 V, which is the upper limit of the variable range, and when the overvoltage of the output voltage Vo, which is the overvoltage in that case, becomes 6.5 V, the output voltage Vo becomes overvoltage at 6.0 V, which is 6.5 V or less. Although it is not necessary to perform the protection operation, the Zener diode Z1 conducts and the overvoltage detection is performed by the control unit 14.
And the operation of overvoltage protection is performed.

[0007]

According to the present invention, the output voltage is controlled so as to become a set voltage, and when an output voltage is detected as being in an overvoltage state exceeding a reference value, a predetermined protection is provided. The above-described problem is solved by a power supply device that operates, which is configured to vary a reference value for overvoltage detection in accordance with setting of an output voltage.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. In this embodiment, a power supply device is described as being applied to a switching power supply, but the present invention is not limited to this switching power supply and can be applied to other power supply devices.

FIG. 1 is a circuit diagram of a power supply device according to an embodiment of the present invention. Parts corresponding to those in FIG. 2 are denoted by the same reference numerals, and detailed description of the same reference numerals is omitted. I do. In the present embodiment, the overvoltage detection unit 12 includes the comparator CP1, the photocoupler PC1, and the resistors R3 and R3.
4, R5. In the overvoltage detection unit 12, a series connection of the resistors R3 and R4 is connected between the output terminals, a connection point c between the resistors R3 and R4 is connected to the input (-) of the comparator CP1, and the output voltage A connection point b between the variable resistor VR1 and the resistor R2 of the detection section 8 is connected to the other input section (+) of the comparator CP1. In this embodiment, the comparison feedback unit 10 includes a comparator 10a,
It is illustrated separately with a feedback unit 10b composed of a photocoupler.

The operation will be described below.

When the output voltage Vo is set high, the volume value of the variable resistor VR1 (setting means) of the output voltage detecting section 6 is reduced. Then, the voltage at the connection point a, that is, the detection value Vd1 with respect to the input portion (-) of the comparator 10a becomes smaller. As a result of the comparison between the detection value Vd1 at the comparator 10a and the reference value Vref1, the comparator 10a outputs A comparison output for increasing the output voltage Vo is output to 14.
As a result, the output voltage Vo is increased by the control unit 14 performing a control operation on the converter unit 4 so that the detected value Vd1 matches the reference value Vref1.

On the other hand, when the volume value of the variable resistor VR1 is reduced, the voltage between both ends of the resistor R2 of the output voltage detector 6 is increased. In this case, the voltage between both ends of the resistor R2 is used as a reference value Vref2 for overvoltage detection with respect to the input (+) of the comparator CP1 of the overvoltage detection unit 12, and the voltage between both ends of the resistor R4 is used as the input (−) of the comparator CP1. ) For the detected value V
The comparator CP1 compares the reference value Vref2 with the detection value Vd2. Therefore, since the reference value Vref2 increases in the comparator CP1, it is determined that the output voltage Vo is in an overvoltage state unless the output voltage Vo from the comparator CP1 is higher than before the volume value of the variable resistor VR1 is reduced. The comparison output is not output.

When the output voltage Vo is set low, the volume value of the variable resistor VR1 is increased. Then, in this case, contrary to the above, the reference value Vref2 for detecting the overvoltage decreases. The comparator CP1 outputs a comparison output in which the output voltage Vo is in an overvoltage state even when the output voltage Vo is lower than before increasing the volume value of the variable resistor VR1.

Therefore, in the power supply device according to the embodiment, when the output voltage Vo is set high, the reference value for overvoltage detection increases, and when the output voltage Vo is set low, the reference value for overvoltage detection decreases. This solves the conventional problem. That is, the variable range of the output voltage Vo can be set to, for example, 4.5 V to 5.5 V by adjusting the variable resistor VR1, and the specification of the load connected to the output is such that when the output voltage Vo is, for example, 5V, an overvoltage occurs. For example, when the voltage is set to 6V, the volume value of the variable resistor VR1 is increased by another load specification to increase the output voltage Vo to, for example, 4.5V.
In response to this, the overvoltage is automatically changed correspondingly to, for example, 5.5 V, and the volume value of the variable resistor VR1 is reduced according to another load specification to reduce the output voltage Vo to, for example, Even if the voltage is set to a high value of 5.5 V, the overvoltage is automatically changed to, for example, 6.5 V, which is convenient for the user. Therefore, the above-described problem caused by the fixed reference value for overvoltage detection as in the related art is solved.

The above is proved by a mathematical formula.

First, the value of the output voltage Vo is given by the following equation (1).

Vo = [1 + R1 / (R2 + VR1)] × Vref1 (1) where R1 is the resistance value of the resistor R1, R2 is the resistance value of the resistor R2, VR1 is the resistance value of the variable resistor VR1, and Vref1
Is a reference value of the comparator 10a.

Further, the reference value Vref2 for overvoltage detection with respect to the input (+) of the comparator CP1 of the overvoltage detector 12 is provided.
Is given by the following equation (2).

Vref2 = (1 + R3 / R4) × Vr2 = (1 + R3 / R4) × [R2 / (R2 + VR1)] × Vref1 (2) where R3 is the resistance of the resistor R3, R4 is the resistance of the resistor R4, Vr2 is a voltage between both ends of the resistor R2.

To increase the output voltage Vo, the volume value of the variable resistor VR1 is reduced. Here, assuming that the resistance value VR1 of the variable resistor VR1 is zero, the reference value Vref2 for overvoltage detection is given by the following equation (3).

Vref2 = (1 + R3 / R4) × Vr2 = (1 + R3 / R4) × Vref1 (3) Accordingly, the reference value Vref2 for overvoltage detection increases by the following equation (4).

(1 + R3 / R4) × Vref1 [1−R2 / (R2 + VR1)] (3) When the output voltage Vo is set low, the reference value Vref2 for overvoltage detection decreases, contrary to the above.

As a result, the above-mentioned conventional disadvantages such as a more suitable reference value for overvoltage detection for a connected load are automatically set without requiring a user's setting operation. For example, the output voltage detector 8
In the case where the reference value Vref2 of the overvoltage detection unit is set using a variable resistor or the like provided separately from the setting operation of the variable resistor VR1, the user needs to set the output voltage Vo and the reference value Vref2 for overvoltage detection. It is necessary to perform the setting operation, and the setting operation becomes complicated and erroneous operation is likely to occur. However, in this embodiment, the reference value Vref2 for overvoltage detection is automatically set simultaneously with the setting of the output voltage Vo only by operating the variable resistor VR1. This is convenient.

[0024]

As described above, according to the present invention, the output voltage is controlled so as to become the set voltage, and when it is detected that the output voltage is in an overvoltage state exceeding the reference value, a predetermined value is obtained. In the power supply device performing the protection operation, the reference value of the overvoltage detection is configured to be variable according to the setting of the output voltage. Therefore, when the output voltage is set to be low, the overvoltage detection reference value also corresponds to the reference value. Since it is variable, unlike the related art, there is no problem that the overvoltage protection operation is not performed depending on the connected load.

Further, according to the present invention, unlike the related art, it is not necessary to separately add a circuit for externally performing an overvoltage protection operation corresponding to the connected load, which is advantageous in terms of cost. The size of the entire apparatus is not increased.

Further, according to the present invention, unlike the related art, there is no disadvantage that the overvoltage protection operation does not need to be performed but the overvoltage protection operation works.

According to the present invention, when the output voltage setting means is provided so that the reference value of the overvoltage detection is varied together with the output voltage by the setting operation of the setting means, the output voltage setting operation can be performed by the user. The setting of the reference value for overvoltage detection is automatically performed only by using the setting function.Therefore, if the operation of setting the output voltage and the operation of setting the reference value of overvoltage detection are separated, the complexity of the setting operation and the occurrence of erroneous operations are considered. Will be resolved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional power supply device.

[Explanation of symbols]

 Reference Signs List 2 input rectifying / smoothing unit 4 converter unit 6 output rectifying / smoothing unit 8 output voltage detecting unit 10a comparator 10b feedback unit 12 overvoltage detecting unit 14 control unit

Claims (2)

[Claims] 1. A power supply device for controlling an output voltage to be a set voltage and performing a predetermined protection operation when detecting that the output voltage is in an overvoltage state exceeding a reference value. Wherein the reference value for overvoltage detection is varied in accordance with the setting of the power supply. 2. The power supply device according to claim 1, further comprising output voltage setting means, wherein a reference value for overvoltage detection is varied together with the output voltage by setting operation of the setting means.
A power supply device, characterized in that: