JPS63174518A - Constant voltage source circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a constant voltage power supply circuit using a three-terminal regulator, and in particular, it prevents defects in the constant voltage output value when low voltage is input to the three-terminal regulator, and It relates to a constant voltage power supply circuit that prevents damage to a three-terminal regulator during input.

[Conventional technology]

Conventionally, in a constant voltage power supply circuit using a three-terminal regulator, when the input voltage of the three-terminal regulator becomes lower than the standard value, that is, during low voltage input, the output voltage of the three-terminal regulator no longer maintains the specified voltage. As the input voltage decreased, the output voltage also gradually decreased.

When inputting a high voltage, it would not output the specified output voltage, and if the voltage was too high, it would destroy the three-terminal regulator.

[Problem that the invention seeks to solve]

The input voltage of a three-terminal regulator is usually created by rectifying and smoothing (DC) an externally supplied power source (AC) through a transformer. When the external power supply fluctuates, the input voltage of the three-terminal gierator will also fluctuate, and the input voltage will drop, making it impossible to maintain a constant voltage output at the time of death, and the output voltage will also drop. If the output of a three-terminal regulator is used for temperature control, motor control, high pressure control, etc., and the output becomes low as described above,
The drawback is that it can become uncontrollable and go out of control, resulting in a very dangerous situation.

[Means for solving problems]

In a constant voltage power supply circuit using a three-terminal regulator, the present invention uses a voltage value obtained by dividing the voltage at the input terminal with a resistor and a constant voltage value created from the voltage at the input terminal as input to a comparator, and connects the input terminal and the three-terminal regulator. A switch is connected between the input terminal and the input terminal of the three-terminal regulator, and when the input voltage of the three-terminal regulator becomes lower or higher than the standard value, the comparator output is inverted and the switch is normally turned on. This is a constant voltage power supply circuit characterized by turning off the switch connected to the three-terminal regulator and not supplying power to the load connected to the output of the three-terminal regulator.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows a circuit of one embodiment of the present invention.

The input terminal 1 is supplied with a voltage obtained by rectifying and smoothing an externally supplied power source (AC).

The circuit diagram in FIG. 1 shows resistors 2. It consists of a resistor 3, a Zener diode 4, a comparator 5, a transistor 6, a transistor 7, a three-terminal regulator 8, and a three-terminal regulator output terminal 9.

A voltage value obtained by dividing the input voltage of the three-terminal regulator by the resistors 2 and 3, and a constant voltage value determined by the Zener diode 4 are input to the comparator 5. The voltage value determined by the Zener diode 4 is determined by the three-terminal regulator 8.
The minimum value of the input standard voltage value of resistor 2. It is set to be equal to the voltage value divided by the resistor 3. Tsutb,
For example, assume that the lowest input standard voltage value of a three-terminal regulator is 7V. 7■ Resistance 2. The voltage divided by resistor 3 is 5v
In this case, the constant voltage value created by the Zener diode is 5
The operating voltage of comparator 5 is set to be 2v.
IC with a wide range of ~36V (e.g. μpc393
), it can also be applied to three-terminal regulators with low input standard voltage values.

The operation of the circuit shown in FIG. 1 will be explained using FIG. 2.

FIG. 2(a) shows the input voltage input from input terminal 1 of FIG.

FIG. 2(b) shows the output voltage when the input voltage of FIG. 2(a) is directly applied to the three-terminal regulator. Figure 2 (
Until the input voltage value in a) reaches the lowest value of the input standard voltage value at point A, the three-terminal regulator outputs the standard voltage value as shown in (b).

However, when the input voltage value becomes lower than the voltage value at point A, (
As shown in b), the output voltage also decreases.

[Example 2] FIG. 3 is a circuit diagram of a second embodiment of the present invention.

The circuit shown in FIG. 3 turns off the input voltage of the three-terminal gate and regulator when the input voltage is high. The operation of the circuit shown in FIG. 3 is such that when the input voltage value of the input terminal 100 becomes higher than the highest standard value, the output voltage of the comparator 14 becomes Ov, the transistor 16 is turned off, and the transistor 15 is turned off. With this three terminals across K, the input voltage of the gierator is turned off, and the output voltage of the output terminal 18 is no longer output. The values of the Zener diode 12, the resistor 11, and the resistor 12 are, for example, when the maximum input standard voltage value of the three-terminal regulator is 30V, the constant voltage value of the Zener diode is 20V, and the value of the resistor 11.
The value divided by the resistor 12 is set so that when the value of the input terminal 10 is 30V, it becomes 20VK.

〔Effect of the invention〕

As explained above, in the present invention, when the fluctuation of the input voltage of the three-terminal regulator falls below the minimum standard voltage value, the comparator switches the three terminals to stop supplying the input voltage to the gierator, and the input voltage of the three-terminal regulator is By not outputting the output voltage, it has the effect of preventing the control system that uses this output voltage value from going out of control.When the input voltage fluctuation exceeds the maximum specified voltage value, the comparator is used to prevent the control system from running out of control. This has the effect of turning off the input voltage of the three-terminal geiler and preventing damage to the three-terminal regulator.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is a diagram for explaining the operation of the circuit of the present invention, and FIG. 3 is a circuit diagram showing a second embodiment of the present invention. It is a circuit diagram. 2.3, 11.12・Old...Resistance, 4,13...
・Zener diode, 5, 14... Comparator, 6.7, 15° 16... Transistor,
8.17...Three terminal regulator. Figure 2

Claims (1)

[Claims] In a constant voltage power supply circuit using a three-terminal regulator, the voltage value obtained by dividing the voltage at the input terminal with a resistor and the constant voltage value created from the constant voltage source are input to a comparator, and the input terminal and the input terminal of the three-terminal regulator are connected to each other. A constant voltage power supply circuit characterized in that a switch connected between the circuits is controlled by the output of the comparator.