Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-06-30
2001-05-08
Nguyen, Matthew (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
Reexamination Certificate
active
06229291
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to a current sharing control system of a power supply, wherein a plurality of switching power supplies are connected in parallel to feed DC power to an external load.
2. Description of the Prior Art
A conventional current sharing control system of a power supply using a plurality of switching power supplies to supply DC power to an external load is shown in
FIG. 1
, wherein a convention switching power supply
10
is used as the power supply system and comprises an output current sensing circuit
1
for outputting an output current sensing signal, corresponding to the circuit's output current. The sensing circuit
1
is connected to the negative input terminal of an error amplifier U
2
through a resistor R
12
. Also, an output voltage sensing circuit
2
, which outputs an output voltage sensing signal, corresponding to the circuit output voltage, is connected to the negative input terminal of an error amplifier U
1
.
The positive input terminal of the error amplifier U
1
is connected to a voltage reference Vrl and the amplifier output terminal is connected to the anode of diode D. The cathode of diode D is connected to both the negative input terminal of error amplifier U
2
, through a resistor R
11
, and a parallel operation control signal terminal CT. The positive input terminal of error amplifier U
2
is connected to a reference voltage Vr
2
and the output terminal thereof is connected to a switching regulator
3
.
The switching regulator
3
is a DC power supply circuit, whose output current is controlled by the output of error amplifier U
2
. The switching regulator
3
comprises a pulse width modulation circuit
3
a
, that modulates the output of error amplifier U
2
by pulse width, and a switching converter
3
b
, that inputs the output of pulse width modulation circuit
3
a
to a switching device. The output of switching converter
3
b
is connected to output terminals OUT+ and OUT−. The output terminals CT, OUT+ and OUT− of the plurality of switching power supplies
10
,
10
a
, and
10
b
, as described above, are connected in parallel as depicted in
FIG. 2
, in order to supply power to a load
50
. The sum of the output currents of the switching power supplies
10
,
10
a
and
10
b
is thus supplied to load
50
. Although
FIG. 2
shows the case of three switching power supplies
10
,
10
a
,
10
b
connected in parallel, it is possible to increase or decrease the number of power supplies according to the current capacity required by load
50
.
In each switching power supply, connected as shown in
FIG. 2
, a voltage signal, which corresponds to the power supply output current, detected by the output current sensing circuit
1
of the power supply (called output current sensing signal Vc) is compared with the voltage of the voltage reference Vr
1
by means of the error amplifier U
1
(see FIG.
1
). The resulting comparison signal is outputted to parallel operation control signal terminal CT through diode D.
Since the parallel operation control signal terminals CT of the plurality of switching power supplies
10
,
10
a
,
10
b
are connected in parallel, the highest level of signals outputted from the terminals CT of the parallel connected switching power supplies (called parallel operation control signals Vp) is supplied to the resistor R
11
of each switching power supply by the operation of diode D. The switching power supply that outputs the highest level parallel operation control signal Vp serves as a master switching power supply for controlling the other switching power supplies.
For each parallel connected switching power supply, a parallel operation control signal Vp outputted by the master switching power supply is added to the output current sensing signal Vc of the parallel connected switching power supply by means of resistors R
11
and R
12
, and error amplifier U
2
. The resulting addition signal is compared with the reference voltage Vr
2
, and the resulting comparison output signal is fed to switching regulator
3
through error amplifier U
2
.
The switching regulator
3
of each switching power supply controls the power supply output current according to the comparison output signal supplied by error amplifier U
2
. Thus, in the current sharing control system of the power supply,described above, it is possible to control the output currents of the parallel connected plurality of switching power supplies , to substantially the same level by setting the power supplies reference voltage Vr
2
to the same value.
As discussed, in the conventional current sharing control system of a power supply, it is possible to control the output currents of a plurality of parallel connected switching power supplies to the same level with accuracy. However, the conventional systems have a problem, namely, that if a switching power supply, serving as the master switching power supply, fails or is connected or disconnected while the power line is active, the output voltage variation becomes unacceptably large for a short period of time during which another switching power supply takes the place of the master switching power supply.
Furthermore, disadvantageously, in the conventional system, the output voltage of the switching power supply, other than the master switching power supply, is not directly controlled. Instead, the concerned power supply is controlled in such a manner that the sum of the parallel operation control signal and the power supply output current is kept constant. This results in a problem, namely, that the output voltage variation becomes unacceptably large when an output voltage sensing circuit, such as a current transformer, which involves a certain delay of detection, is used.
SUMMARY OF THE INVENTION.
Accordingly, an object of the invention is to overcome the aforementioned and other disadvantages and deficiencies of the prior art.
Another object is to provide a current sharing control system of a power supply that enables the output currents of a plurality of parallel connected switching power supplies to be maintained at the same level, thereby preventing output voltage variations in the power supplies from occurring in the event any one or more switching power supplies fail, or are connected, or disconnected while the power line is still active.
A further object is to provide such system which enables control of the output voltage variations to be within a certain range when short circuiting or open circuiting occurs in a parallel operation control signal used in such system.
REFERENCES:
patent: 3710254 (1973-01-01), Kusui
patent: 5862044 (1999-01-01), Shioya et al.
patent: 5939991 (1999-08-01), Deng
Matsumura Hideaki
Murakami Hiroyuki
Kojima Moonray
Nguyen Matthew
Yokogawa Electric Corporation
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