Electric power conversion systems – Current conversion – Having plural converters for single conversion
Reexamination Certificate
2000-07-17
2001-10-16
Han, Jessica (Department: 2838)
Electric power conversion systems
Current conversion
Having plural converters for single conversion
C363S069000
Reexamination Certificate
active
06304470
ABSTRACT:
TECHNICAL FIELD
The present invention relates to power supply devices, and more particularly to improvements in an output voltage drop at the time of parallel operation of a DC/DC converter.
BACKGROUND ART
Field of the Invention
FIG. 1
is a diagram showing a configuration of a conventional device. The conventional device is arranged so that a first DC/DC converter
10
(DC/DC converter
1
) and a second DC/DC converter
20
(DC/DC converter
2
) are connected in parallel with a load via diodes for parallel operation so that power can be supplied to the load.
When a switching element TR
1
is ON, an input voltage E is switched by the switching transistor TR
1
. C
1
is a condenser for noise elimination connected across the input voltage E. As shown, an FET is used as the switching element TR
1
. A primary winding of a power transformer T is connected as a load of the FET. The switching element TR
1
is driven by a control part (CONT)
1
. For example, PWM (pulse width modulation) is used as a driving method. That is, by controlling the ON time in a clock cycle, the switching element TR
1
is controlled so that an output voltage E
01
is kept constant.
A high-frequency alternating current introduced on a secondary side of the power transformer T when the switching element TR
1
is ON is converted into a direct current voltage by means of a full-wave rectifying circuit made up of diodes D
1
and D
2
. The direct current voltage is applied to a smoothing condenser C
2
via a smoothing coil L
1
, and is regulated so as to be a flat direct current voltage. R
1
, R
2
and R
3
are resistors connected between an output line and a common line, and have th function of dividing the output voltage. R
4
is a resistor connected between the output line and the common line.
The output voltage supplies power to a load
2
via a diode D
3
for parallel operation (parallel connection). The output voltage obtained at that time is divided by the voltage dividing circuit made up of the resistors R
1
~R
3
, and a divided voltage is applied to the control part
1
as the output voltage. The control part
1
compares the output voltage with a reference value and controls the ON time of the switching element TR
1
so that both the values coincide with each other (PWM control).
When the switching element TR
1
is OFF, energy stored in the smoothing coil L
1
passes through a loop of smoothing condenser C
2
→parallel operation diode D
3
→load
2
→and diode D
2
, and current is supplied to the load
2
.
The foregoing is directed to the operation of the DC/DC converter
1
, and an operation of the DC/DC converter
2
is the same as the above. Power (current I
0
) is supplied to the load
2
by the two DC/DC converters.
In the above-mentioned circuit, it is necessary to add block diodes (diodes for parallel operation) in order to prevent, when one of the DC/DC converters becomes abnormal at the time of parallel operation, the other DC/DC converter from being affected.
In the above-mentioned circuit, power is supplied to the load
2
via the parallel operation diodes D
3
. Thus, if the load current increases, the voltage drop developing across the diode D
3
increases, and the output vs. voltage characteristic obtained at this time is as shown in FIG.
2
. As the output current I
0
increases, the output voltage E
01
is decreased due to the voltage drop developing across the diode D
3
, and is dropped by &Dgr;V
1
about the rated current. Thus, the output voltage at that time becomes as shown in
FIG. 2
, and a drop of the output voltage may prevent a communication device serving as the load from normally operating.
The present invention is made taking into consideration the above problems, and has an object of providing a parallel operating device of a DC/DC converter capable of suppressing a drop of the output voltage at the time of parallel operation.
DISCLOSURE OF THE INVENTION
The present invention is a power supply device supplying, in parallel, power from a plurality of DC/DC converters to a common load, there is provided an output compensation circuit which is provided on an output side of each of the DC/DC converters and improves an output voltage due to a voltage drop developing across a diode for parallel operation,
The above-mentioned output compensation circuit may be constructed so as to be a circuit which improves the output voltage due to the voltage drop developing across the diode for parallel operation, in which: a first diode is connected via a resistor to one end of the diode for parallel operation; a second diode is connected via another resistor to another end of the diode for parallel operation; and yet another resistor is connected between cathodes of the first and second diodes and an output terminal.
The above-mentioned output compensation circuit may be constructed so as to a circuit which detects an increase in an output current and increases a voltage of an anode side of the diode for parallel operation.
REFERENCES:
patent: 4860188 (1989-08-01), Bailey et al.
patent: 5612581 (1997-03-01), Kageyama
patent: 6229723 (2001-05-01), Umetsu et al.
patent: 6-105464 (1994-04-01), None
patent: 6-36388 (1994-05-01), None
patent: 9-093931 (1997-04-01), None
Isago Tomiyasu
Ogawa Hiromitsu
Fujitsu Limited
Han Jessica
Helfgott & Karas, PC
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