JPH03280114A - Power supply circuit - Google Patents

Abstract

PURPOSE:To reduce the loss of power and to decrease output fluctuation when a power supply voltage is fluctuated by providing a power supply voltage supervisory and controlling means, which closes an opening/closing means when the voltage is dropped and reaches a first voltage and opens the means when the voltage is boosted and reaches a second voltage, and obtaining a hysteresis characteristic in an opening/closing operation to the change of the power supply voltage. CONSTITUTION:An opening/closing means 40 is provided to connect a second resistor 30 between a power source and a load 10 in parallel with a first resistor 20 in the closed state. Further, a power supply voltage supervisory and controlling means 50 is provided to monitor the power supply voltage and to output a control signal so that the opening/closing means 40 can be closed when the voltage is dropped and reaches the first voltage V1 and that the opening/closing means 40 can be closed when the voltage is boosted and reaches the second voltage V2. Then, the opening/closing means 40 is opened/closed with the hysteresis characteristic to the change of the power supply voltage. Thus, the power supply circuit can be obtained to reduce the output fluctuation and the loss of the power even when the power supply voltage is fluctuated.

Description

[Detailed Description of the Invention] [Summary] To provide a power supply circuit that supplies power to a load and that has low power loss and can reduce output fluctuations even when the power supply voltage fluctuates. a first resistor having one terminal connected to the load and the other terminal connected to the power supply; and a first resistor having one terminal connected to the load and the other terminal connected to the power supply through switching means. a switching means connecting the second resistor in the "closed" state in parallel with the first resistor between the load and the power supply; When the voltage reaches the second voltage, the switching means is closed, and as the voltage increases, the second
power supply voltage monitoring and control means that outputs a control signal to open the switching means when the voltage reaches the voltage of , and is configured to operate with hysteresis characteristics.

[Industrial application field]

The present invention relates to a power supply circuit that supplies power to a load.

In order to guarantee the operation of various circuits in communication devices and electronic devices, even when the input power supply voltage fluctuates,
It is necessary to keep the signal output voltage within a certain standard value, and for this reason, a power supply circuit that can keep the power supply voltage supplied to the load constant even if the input power supply voltage fluctuates is required. Become.

Such power supply circuits are required to have stable operation and low power loss.

[Conventional technology]

FIG. 5 shows a diagram illustrating a conventional example.

The conventional example shown in FIG. 5 includes a Zener diode D1 that keeps the output voltage constant, a resistor R7 whose one terminal is connected to the power supply and the other terminal connected to the Zener diode D1, and a Zener diode D1.
1 and resistor R7 (hereinafter referred to as a point) and the load.

When the power supply voltage increases in this circuit, the Zener diode D
The current flowing through point 1 to the ground increases, the voltage drop across resistor R7 increases, and the voltage at point 2 is maintained at the Zener voltage of Zener diode D1.

Conversely, when the power supply voltage becomes lower in this circuit, the current flowing through the Zener diode D1 to the ground decreases, the voltage drop at the resistor R7 becomes smaller, and the voltage at point ■ is maintained at the Zener voltage of the Zener diode D1. be done.

[Problem to be solved by the invention]

When the load is a pulse circuit, there is a large difference in the current flowing through the load when the pulse circuit is "on" and when the pulse circuit is "off."

With such a pulse circuit as a load, in order to keep the power supply voltage supplied to the load constant using the conventional circuit described above, the load current IL and the current IDI flowing through the Zener diode must be
It is necessary to make the relationship IDI It, which results in large power loss.

SUMMARY OF THE INVENTION An object of the present invention is to provide a power supply circuit that has low power loss and can reduce output fluctuations even when the power supply voltage fluctuates.

[Means to solve the problem]

FIG. 1 shows a block diagram illustrating the invention in detail.

In the block diagram of the principle of the present invention shown in FIG. 1, 10 is a load, 20 is a first resistor whose one terminal is connected to the load lO, and the other terminal is connected to the power supply, and 30 is a One terminal is connected to the load 10 and the other terminal is connected to the switching means 4
A second resistor is connected to the power supply through 0.

Further, 40 is a switching means that connects the second resistor 30 in parallel to the first resistor 20 between the power supply and the load 10 in the "closed" state, and 50 monitors the power supply voltage and detects the voltage. When the voltage drops and reaches the first voltage V1, the opening/closing means 40 is
When the voltage rises and reaches the second voltage V2, the power supply voltage monitoring control means outputs a control signal to open the opening/closing means 40. This problem is solved by operating the "open" and "close" operations with hysteresis characteristics in response to changes in power supply voltage.

[For production]

The power supply voltage is monitored by the power supply voltage monitoring control means 50, and when the voltage drops from the upper limit voltage and reaches the first voltage 1, a control signal is output to close the opening/closing means 40, and the first The resistor 20 and the second resistor 30 are connected in parallel to reduce the combined resistance and reduce the voltage drop, and when the voltage rises from the lower limit voltage and reaches the second voltage ■2. , by outputting a control signal to open the switching means 40 and connecting only the first resistor 20 between the power source and the load 10, increasing the resistance value and increasing the voltage drop. Therefore, even if the power supply voltage fluctuates, the voltage supplied to the load can be kept constant.

Here, Vl<V2, and the opening/closing means 40 is operated with a hysteresis characteristic with respect to voltage fluctuations, thereby preventing the opening/closing means 40 from operating frequently in response to small voltage fluctuations.

〔Example〕

The gist of the present invention will be specifically explained below with reference to embodiments shown in FIGS. 2 to 4.

FIG. 2 is a diagram explaining the present invention in detail, FIG. 3 is a diagram explaining the operation of the photocoupler according to the embodiment of the present invention, and FIG. 4 is a diagram explaining the load current according to the embodiment of the present invention. show.

Note that the same reference numerals indicate the same objects throughout the figures.

The embodiment of the present invention shown in FIG. 2 includes transistors TRI, TR2 and output transformer T as the load 10 explained in FIG. In this example, the opening/closing means 40 is composed of a photocoupler 41, the power supply voltage monitoring and controlling means 50 is composed of a reference voltage generation circuit 51, an operational amplifier ○P1, and resistors R1, R4-R6.

In the operation of the above-described circuit, the reference voltage generation circuit 51 generates a reference voltage and inputs it to an example input terminal of the operational amplifier opi.

A voltage obtained by dividing the power supply voltage by resistors R4 to R6 is input to the operational amplifier 0PIO+ side input terminal.

In this circuit, when the input voltage of the + side input terminal becomes lower than the input voltage of the individual input terminal, the operational amplifier OP
I outputs a "low" level, the photocoupler 41 is turned "on", and the resistor R3 is connected in parallel to the resistor R2.

Assuming that there is no resistor R1, the operational amplifier OP1 will turn on or off depending on whether the input voltage at the + side input terminal is thicker (or smaller) than the reference voltage at the - input terminals, so the power supply Photocoupler 4 due to minute fluctuations in voltage
1 turns ``on'' and ``off'' frequently.

Therefore, the output of the operational amplifier OPI is passed through the resistor R1,
By feeding back to the + side input terminal, the operational amplifier OPI
The input/output characteristics of the device are hysteresis characteristics, which prevents frequent turning on and off due to minute fluctuations in the power supply voltage.

This hysteresis characteristic means that, for example, if the power supply voltage is high and the operational amplifier ○P1 is outputting a "high" level, the output will be fed back to the + side input through the resistor R1, and the voltage at the input terminal will be on the + side. Since the bias is applied to the voltage, when the power supply voltage goes further to one side by canceling out this bias, the output of the operational amplifier ○P1 becomes "low".
By operating the operational amplifier OPI in this manner, a rehysteresis characteristic can be obtained.

FIG. 3 shows the operation of the photocoupler 41. When the power supply voltage falls below the upper limit voltage, the first voltage 1 changes from "off" to "on" and the power supply voltage rises above the lower limit voltage. When the power is turned on, the second voltage v2 changes from "on" to "off".

FIG. 4 is a diagram explaining the load current. When the power supply voltage increases from the lower limit voltage due to the operation of the photocoupler 41 as shown in FIG.
The current I increases along the line 2, and when the voltage reaches 2, the resistor R3 turns "off" and operates along the line 2.

Conversely, when the power supply voltage drops from the upper limit voltage, only the resistor R2 is connected in series with the load 10, and the current
decreases along the line (■), and when the voltage reaches (1), the resistor R3 is connected in parallel to the resistor R2, and the current increases or decreases along the line (■).

With the above configuration, it is possible to reduce output fluctuations and reduce power loss by inserting and removing resistors in accordance with fluctuations in power supply voltage.

〔Effect of the invention〕

According to the present invention as described above, it is possible to provide a power supply circuit that has less output fluctuation (and less power loss) even when the power supply voltage fluctuates.

[Brief explanation of drawings]

FIG. 1 is a block diagram explaining the present invention in detail, FIG. 2 is a diagram explaining the present invention in detail, FIG. 3 is a diagram explaining the operation of a photocoupler according to an embodiment of the present invention, and FIG. A fifth diagram explaining the load current of the embodiment of the present invention.
The figures are diagrams illustrating a conventional example. In the figure, 10 is a load, 20 is a first resistor, 30 is a second resistor, 40 is a switching means, 41 is a photocoupler, 50 is a power supply voltage monitoring control means, 51 is a reference voltage generation circuit, and OPl is an operational amplifier. , R1 to R8 are resistors, DI is a Zener diode, TRI and TR2 are transistors, and T is a transformer. Block diagram for explaining the power supply in detail of the present invention Fig. 1 Fig. 2 ■0 ■1 ■2 3 Figure 3
Figure ■0 ■1 ■2 ■3 While explaining the load current of the embodiment of the present invention, Figure 4 to power supply Figure 5

Claims (1)

[Scope of Claims] A power supply circuit that supplies power to a load (10), one terminal of which is connected to the load (10), and the other terminal of which is connected to a power supply. ), a second resistor (30), one terminal of which is connected to the load (10) and the other terminal of which is connected to the power supply through the switching means (40); switching means (40) for connecting a resistor (30) in parallel with the first resistor (20) between the load (10) and the power source; When the voltage reaches the second voltage (V1), the switching means (40) is closed, and when the voltage increases and reaches the second voltage (V2), the switching means (40) is closed.
power supply voltage monitoring and control means (50) that outputs a control signal that causes the switching means (40) to be "open"; A power supply circuit characterized by operating with hysteresis characteristics.