JPS5864515A - Feeding circuit - Google Patents

Abstract

PURPOSE:To feed stable electric power to a distance regardless of variation in load by flowing a prescribed current to an electronic load when a load current less than a prescribed value is detected by a monitoring circuit, and suppressing variation in input voltage against a load current less than a predetermined value. CONSTITUTION:An electronic load 88 is connected in parallel to electronic equipment 44 as a load. This load 88 is controllable by an error comparator 66. A voltage generated at a shunt 55 for monitoring a load current flowing through the equipment 44 is compared with the prescribed voltage from a reference voltage source 77 through the error comparator 66. When the current I2 decreases below a specified value, the comparator 66 drives the load 88 to perform control so that the load 88 has impedance corresponding to the load current value. Consequently, input voltage variation against a load current below the prescribed value is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply circuit that supplies stable power to electronic equipment installed at a distance using an intervening line such as a coaxial cable or an optical fiber cable.

FIG. 1 shows the configuration of a conventional power supply circuit.

In FIG. 1, 11 is a power supply source, 22 is a power supply line,
33 is a constant pressure for electronic equipment installed far away.
B. It is a DC-DC converter that supplies power.

The most efficient power supply (distance of power supply at constant power) is determined here.
In order to maximize U), the required power of the electronic equipment and the power loss of the feeder line must be selected to be equal. That is, it has the relationship shown in FIG.

R represents the loop resistance of the power supply line, and η represents the conversion efficiency of the DC-I)C converter 33.

- The squid supply source 11 can be either a constant voltage source or a constant current source, but conventionally, for long-distance power supply for transportation, constant current is used because a constant current can be obtained from a repeater and it is less affected by voltage drop in cables. @den is used for rNr.

The case where the power supply source 11 is a constant current source will be explained below.

Do the light.

Now, in a power supply system as shown in Figure 1, electronic equipment 4
There is no problem if the power consumption of the DC-DC converter 33 is substantially constant, but if it changes significantly, that is, if the load on the DC-DC converter 33 changes significantly, the following problems arise.

From equation (1), DC-1) C converter 330 input voltage■
1 is Vt = 12'J2/7? Io”,,Iz
(2) (V2 and Io are stabilized and constant), so when the load of the DC-DC converter 33 changes, the input 'i' changes accordingly.
If the °C pressure vl changes and the change rate becomes too large, the DC-DC converter will not be able to operate normally.

An object of the present invention is to provide a power supply circuit that solves the above problems.

A power supply according to the present invention to achieve the above object.

The circuit is a power supply circuit that supplies stable power to a load installed at a distance via a power supply line, in which an electronic load is connected in parallel to the load and a circuit for monitoring the load current is provided, and the monitoring circuit described in 61. When a load current of less than a predetermined value is detected, driving the electronic load;
It is configured to allow a predetermined current to flow through the electronic load, and to suppress input terminal fluctuations for load currents below a predetermined value.

According to the above configuration, even when the load changes significantly, the input voltage fluctuation range can be kept small, and the DC-DC
Normal operation of the converter can be ensured.

The present invention will be further described below with reference to the drawings.

FIG. 2 is a circuit diagram showing an embodiment of the power supply circuit according to the present invention. An electronic load 88 composed of a transistor or the like is connected in parallel to the electronic device 44 as a load. This '-': The sensor 88 can be controlled by the error comparator 66.

'Shunt 5 that monitors the load current flowing through electronic equipment■2
The voltage generated at 5 is compared by an error comparator 66 with a reference voltage source 77 that is preset to a predetermined voltage and voltage.

When the load current f2 becomes below a certain value, the error comparator 66 drives the electronic load 88 and controls the electronic load f88 to have an impedance corresponding to the negative current value. At this time, the input voltage V1 of the JT) C--1) C converter has a characteristic as shown in equation (3).

■、−■２■２／η■o＋■ ・・・・・・・・・・・・
(3) Figure 3-1 is a diagram comparing the V and -I2 characteristics of the conventional circuit (dotted line b) and the circuit of the present invention (solid line a).

In the figure, in the circuit of the present invention, when the load current becomes 12 or less, the electronic load becomes conductive, and the current flowing through the electronic device (1) and the electronic load is maintained so that about 4 is equal to I2.
Therefore, even if the load is 1ff and the hood is considerably small, the input voltage ■l will be maintained at approximately ■°, and DC-1)
Normal operation of the C converter 33 is ensured.

FIG. 4 is a circuit diagram showing a second embodiment of the present invention, in which a circuit for monitoring load current is provided on the input side of the DC-DC converter 33. If the load 44 decreases, the input voltage will change accordingly, and the IO will also change. Therefore, when the load current is below the cut-off value, if the error comparator 66 is activated by the circuit that monitors the load current and the electronic load is driven, Vl will be changed to the same value as the solid line in FIG. characteristics.

As explained in detail above, according to the present invention, it is possible to operate a DC-DC converter normally even when the load fluctuates significantly in a power supply system that supplies power to a load installed at a distance via a power supply line. As a result, stable power can be supplied over long distances regardless of load fluctuations.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the configuration of a conventional power supply circuit, Fig. 2 is a circuit diagram showing an embodiment of the power supply circuit according to the present invention, and Fig. 3 is an input voltage-output current of the conventional circuit and the circuit of this embodiment. The characteristic diagram and FIG. 4 are circuit diagrams showing a second embodiment of the present invention. 11...Power supply source 22...Power supply line 33...
・DC-DC converter 44...Load (electronic equipment) 55...Shunt (circuit for monitoring load current) 66.
...Error comparator 77-°°reference voltage source 88...
Electronic load patent applicant Hisashi Inoro, patent attorney representing NEC Corporation

Claims (1)

[Claims] In a power supply circuit that supplies stable power to a load installed far away via a power supply line, an electronic load is connected in parallel to the load, and a circuit for monitoring the load current is provided, and a value determined in advance by the monitoring circuit is provided. When a load current below a predetermined value is detected, the electronic load is driven, a predetermined current is passed through the electronic load, and the input voltage fluctuation is suppressed for a load current below a predetermined value. Characteristic power supply circuit.