JPH06233533A - Overcurrent control circuit of variable output regulator - Google Patents

Abstract

PURPOSE:To comprose input terminals, output terminals, ground terminals, and output voltage adjustment terminals so that output voltage can be adjusted by adjusting control voltage inputted into an output voltage adjustment terminal. CONSTITUTION:This circuit comprises a current detection means consisting of a current detection resistor 41F which detects output current connected to the input side of an output variable regulator 21 (hereinafter the same as an output variable regulator 22) and a comparison means consisting of an operation amplifier 41C which inputs a partial voltage of the input voltage of this output variable regulator 21 as a set value into its - input terminal, and a voltage drop of the current detection resistor 41F into its + input terminal, and which outputs control voltage into the output voltage adjustment terminal of the variable output regulator 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent control circuit for improving the overcurrent protection characteristic of a variable output regulator.

[0002]

2. Description of the Related Art A variable output regulator is a regulator having an output voltage adjusting function and an overcurrent protection function.
It is connected between the DC power supply and the load. As this type of variable output regulator, for example, four-terminal regulator PQ30RV1 / 11, PQ30RV2 manufactured by Sharp Corporation
There is / 21. FIG. 3 is a terminal connection diagram thereof, where is an input terminal, is an output terminal, is a ground terminal, is an output voltage adjusting terminal, and the output voltage can be adjusted by inputting a control voltage to the output voltage adjusting terminal. It can be controlled within the range of 30 V (the output voltage decreases as the control voltage increases). Fig. 4 is the overcurrent protection characteristic diagram. The vertical axis shows the relative output voltage (%) with respect to the rated output voltage, and the horizontal axis shows the relative output current (%) with respect to the rated output current. Current protection value) Q is almost 200% of rated output current
Is.

FIG. 2 is a power supply circuit diagram in which a plurality of output variable regulators, two in FIG. 2, are connected to the output side of a switching power supply device. In FIG. 2, the switching power supply device 1 has positive and negative DC input terminals IP and I.
Primary coil of transformer 1A and switching element 1B at N
Is connected in series, and the rectifying / smoothing circuit 1H including the diodes 1C and 1D, the coil 1E, and the capacitor 1F is connected to the secondary coil of the transformer 1A. The positive and negative side DC output terminals p and n of the rectifying / smoothing circuit 1H are drawn out and connected to the positive and negative side DC output terminals OP and ON. 1G is a control circuit, the input side of which is connected to the positive and negative side DC output terminals p and n of the rectifying / smoothing circuit 1H, and the output side of which is connected to the control terminal of the switching element 1B.

Reference numerals 21 and 22 are variable output regulators, each having an input terminal connected to the positive side DC output terminal OP of the switching power supply device 1, an output terminal connected to the positive side DC load terminal OP1 or OP2, and its ground. Terminal is the negative side DC output terminal of switching power supply 1
And the negative side DC load terminal ON1 or ON2. Further, the output voltage adjusting terminal is a voltage dividing resistor 31 for each output voltage of the output variable regulators 21 and 22, respectively.
It is connected to the voltage dividing point of A, 31B or 32A, 32B.

The operation of this power supply circuit is as follows. First, the operation of the switching power supply device 1 will be described. The switching element 1B has a high frequency by the control circuit 1G,
For example repeatedly turned on and off in a cycle of 100kH _Z. By turning on and off, the primary coil of the transformer 1A is opened and closed, and an AC voltage is induced in the secondary coil of the transformer 1A. This AC voltage is converted into a DC voltage by the rectifying / smoothing circuit 1H and output from the positive and negative output terminals OP and ON. On the other hand, this output voltage is fed back to the control circuit 1G, and the control circuit 1G controls the switching width of the switching element 1B to control the output voltage to a constant value.

The output voltage of the switching power supply device 1 is input to the input side (between the input terminal and the ground terminal) of the output variable regulators 21 and 22, and the positive side and the negative side are supplied from the output side (between the output terminal and the ground terminal). A voltage is output through the side DC load terminals OP1, ON1 or OP2, ON2. And the voltage dividing resistors 31A, 31B or 3
By changing the voltage division ratio of the voltage dividing resistors of 2A and 32B,
This output voltage can be adjusted. When an overcurrent occurs in each load, the overcurrent is limited according to the overload protection characteristic shown in FIG. In this way, the overcurrent is limited, so that even if an overcurrent occurs in one load, the other load is not affected and the power is normally fed. That is, it is possible to supply power from a single-voltage power supply device to a plurality of loads having different voltages.

[0007]

Although the overcurrent protection characteristic of the variable output type regulator is slightly different depending on the manufacturer, the overcurrent protection value Q is generally about 200% of the rated output current as shown in FIG. Therefore, at the time of overcurrent, about twice as much current flows through the switching power supply device (assuming that overcurrent has occurred in both of the two variable output regulators connected to the switching power supply device). For this reason, the switching power supply device may overheat, and in some cases, may burn out.

It is an object of the present invention to provide an overcurrent control circuit that reduces the overcurrent protection value of a variable output regulator as much as possible.

[0009]

In order to achieve the above-mentioned object, an overcurrent control circuit for an output variable regulator according to the present invention comprises a current detecting means for detecting an output current of the output variable regulator, and this current detecting means. When the detected output current exceeds a separately set value, the output voltage adjusting terminal of the output variable regulator is provided with a comparison means for outputting a control voltage. These current detecting means are connected to the input side of the variable output regulator and are composed of a current detecting resistor for detecting an input current proportional to the output current. The comparing means has its negative input terminal receiving the input of this variable output regulator. The voltage corresponding to the voltage is input as the set value, the voltage drop of the current detection resistor is input to the + input terminal, and when the voltage drop of the current detection resistor exceeds the set value, the output voltage of the output variable regulator Use an operational amplifier that outputs a control voltage to the adjustment terminal. Further, the overcurrent control circuit of the output variable regulator is provided in the output variable regulator connected to the switching power supply device.

[0010]

The overcurrent control circuit of the variable output regulator according to the present invention detects the output current of the variable output regulator by the current detection means including, for example, a current detection resistor, and the output current value is, for example, this variable output regulator. When the set value given by the divided voltage of the input voltage of is exceeded,
Since the control voltage is output to the output voltage adjusting terminal of the output variable regulator, for example, the comparing means including an operational amplifier is provided, the control voltage is output when the output current exceeds the set value due to an overcurrent. Is input to, the output voltage drops, and the overcurrent is limited. That is, the overcurrent protection value of the variable output regulator decreases.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a power supply circuit diagram in which a plurality of variable output regulators having an overcurrent control circuit of the present invention are connected to the output side of a switching power supply device, two in FIG. 1 is an output variable regulator 21 shown in FIG.
(Because the same applies to the variable output regulator 22, the variable output regulator 21 will be described below.)
Includes an overcurrent control circuit 41 connected between the switching power supply device 1 and the variable output regulator 21. The overcurrent control circuit 41 includes a positive side DC output terminal OP and a negative side DC output terminal ON of the switching power supply device 1.
A voltage dividing resistor 41A that is connected between and to divide the input voltage,
41B, an input current that is connected between a connection point between the ground terminal of the variable output regulator 21 and the negative side DC load terminal ON1 and the negative side DC output terminal ON of the switching power supply device 1 and that is proportional to the output current. Of the current detection resistor 41F for detecting the voltage, the negative input terminal thereof is at the voltage dividing point of the voltage dividing resistors 41A and 41B, and the positive input terminal thereof is the variable output regulator 2
The output terminal of the first grounding terminal is composed of a current limiting resistor 41D and an operational amplifier 41C connected to the output voltage adjusting terminal of the output variable regulator 21 via a diode 41E.

The operation of this power supply circuit is as follows. When an overcurrent occurs in the positive and negative side DC load terminals OP1 and ON1, the input current of the variable output regulator increases and the voltage drop of the current detection resistor 41F increases. This voltage drop is applied to the-input terminal of the operational amplifier 41C. When the input voltage of the output voltage of the switching power supply device 1 exceeds the voltage (giving the set value of the overcurrent), the control voltage is output from the output terminal through the current limiting resistor 41D and the diode 41E, and the output variable regulator 21 The control voltage determined by the voltage dividing resistors 31A and 31B input to the output voltage adjusting terminal is increased. Since the output voltage of the variable output regulator 21 decreases as the control voltage input to the output voltage adjusting terminal increases, its output current is limited. Then, by adjusting each resistance value of the voltage dividing resistors 41A and 41B and adjusting the value of the divided voltage, the set value of the overcurrent, that is, the protection value of the overcurrent can be arbitrarily determined.

As a result, the overcurrent protection value can be lowered, the increase in the current flowing through the switching power supply device at the time of overcurrent can be suppressed to a minimum, and the overheat or burnout accident can be prevented. Although the power supply circuit using the switching power supply device has been described in FIG. 1, the present invention is not limited to the switching power supply device, and the same applies to other power supply devices. Further, in FIG. 1, the case where a plurality of output variable regulators are connected has been described, but it is needless to say that the effect of lowering the overcurrent protection value is also obtained in the case of a single output regulator (in this case, the output voltage is Since the output power regulator can be adjusted with the switching power supply, the overcurrent protection function is the main function.

[0014]

According to the present invention, since the overcurrent protection value of the variable output regulator can be lowered, for example, by connecting a plurality of variable output regulators of a switching power supply device,
When power is supplied to a plurality of loads having different voltages, an increase in the current of the switching power supply device can be suppressed to a minimum even if an overcurrent occurs, and the overheating or burnout accident can be prevented.

[Brief description of drawings]

FIG. 1 is a power supply circuit diagram when a plurality of variable output regulators each including an overcurrent control circuit of the present invention are connected to a switching power supply device.

FIG. 2 is a power supply circuit diagram when a plurality of normal output variable regulators are connected to a switching power supply device.

FIG. 3 is a terminal wiring diagram showing an example of an output variable regulator.

FIG. 4 is an overcurrent protection characteristic diagram of the variable output regulator shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 switching power supply device 21 output variable type regulator 22 output variable type regulator 41 overcurrent control circuit 41A voltage dividing resistor 41B voltage dividing resistor 41C operational amplifier (comparing means) 41F current detecting resistor (current detecting means) 42 overcurrent control circuit input terminal ( Variable output regulator) Output terminal (variable output regulator) Ground terminal (variable output regulator) Output voltage adjustment terminal (variable output regulator)

Claims (3)

[Claims] 1. An overcurrent control circuit for an output variable regulator having an input terminal, an output terminal, a ground terminal, and an output voltage adjusting terminal, the output voltage of which is adjusted by adjusting a control voltage input to the output voltage adjusting terminal. In addition, when the output current detected by the output variable regulator and the output current detected by the current detector exceeds a separately given set value, the output voltage adjustment of the output variable regulator is performed. An overcurrent control circuit for an output variable regulator, comprising: a comparison means for outputting a control voltage to a terminal. 2. The overcurrent control circuit of the variable output regulator according to claim 1, wherein the current detecting means is connected to the input side of the variable output regulator and detects an input current proportional to the output current. The comparing means is composed of a resistor, the minus input terminal of which receives the input voltage of the variable output regulator as a set value, and the plus input terminal of which the voltage drop of the current detecting resistor is input. An overcurrent control circuit for an output variable regulator, comprising: an operational amplifier for outputting a control voltage to the output voltage adjusting terminal of the output variable regulator when the voltage drop exceeds the set value. 3. An overcurrent control circuit for an output variable regulator according to claim 1, which is provided in an output variable regulator connected to a switching power supply device.