Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-07-25
2003-02-25
Sterrett, Jeffrey (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S065000
Reexamination Certificate
active
06525947
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power supply apparatus having a reverse flow-preventive diode provided in an output line thereof, and to a power supply system having a plurality of such power supply apparatuses connected in parallel to each other.
2. Description of the Related Art
There has been proposed a power supply system having a plurality of power supply apparatuses connected in parallel to each other. Since the power supply apparatuses are connected in parallel to each other, the power supply system can supply a load with a large power. And, even though any one of the power supply apparatuses fails, the failed one can be backed up by another normal one.
FIG. 1
shows a conventional power supply system having two flyback type switching converters connected in parallel to each other. The conventional power supply system is generally indicated with a reference
100
.
As shown, the conventional power supply system
100
includes a first switching converter
101
and a second switching converter
102
, which are connected in parallel to a load
103
. The first and second switching converters
101
and
102
are identical in circuit configuration with each other. Therefore, the circuit configuration of only the first switching converter
101
will be explained hereinafter.
The first switching converter
101
includes an AC input terminal
111
, an input filter
112
and a rectifying circuit
113
.
The first switching converter
101
is supplied with, for example, a commercial AC power by applying a commercial AC voltage to the AC input terminal
111
. The AC voltage is then applied to the input filter
112
. The input filter
112
is provided to remove a power noise from the input AC voltage, and then the AC voltage with no power noise is applied to the rectifying circuit
113
. The rectifying circuit
113
rectifies the AC voltage to provide a DC input voltage (V
in
) of a predetermined value.
The first switching converter
101
further includes a transformer
114
having a primary winding
114
a
and a secondary winding
114
b
, a switching element
115
, a pulse width modulating (PWM) circuit
116
, a rectifier diode
117
and a smoothing capacitor
118
.
The primary winding
114
a
of the transformer
114
has one end thereof connected to the rectifying circuit
113
which applies the DC input voltage (V
in
) to that end of the primary winding
114
a
. The primary winding
114
a
of the transformer
114
has the other end thereof connected to the ground via the switching element
115
. The switching element
115
is, for example, a field effect transistor (FET). The switching element
115
has the gate thereof connected to the PWM circuit
116
, and is driven in a pulsed manner by a PWM signal supplied from the PWM circuit
116
. The switching element
115
is pulse-driven by the PWM signal to switch a current through the primary winding
114
a
of the transformer
114
.
The secondary winding
114
b
of the transformer
114
has one end thereof connected to the ground. The secondary winding
114
b
of the transformer
114
has the other end thereof connected to the anode of the rectifier diode
117
. The rectifier diode
117
has the cathode thereof connected to the ground via the smoothing capacitor
118
. The connection point at which the cathode of the rectifier diode
117
and the smoothing capacitor
118
are connected to each other will be referred to as D point. At the secondary winding
114
b
of the transformer
114
, a voltage is induced from the primary winding
114
a
due to the switching operation of the switching element
115
. The rectifier diode
117
rectifies, and smoothing capacitor
118
smooths, the voltage induced at the secondary winding
114
b
to generate a DC voltage (V
P
) at the D point.
The first switching converter
101
further includes a voltage divider
119
, a voltage divider
120
, a differential amplifier
121
to detect output voltage error, a reference voltage source
122
to generate a reference voltage (V
ref
) and a photocoupler
123
consisting of a light emitting diode
124
and a phototransistor
125
.
The voltage dividers
119
and
120
are connected in series between the D point and ground. The differential amplifier
121
has an inverting input terminal connected to a connection point between the voltage dividers
119
and
120
, and has a non-inverting input terminal connected to a positive terminal of the reference voltage source
122
. The reference voltage source
122
has a negative terminal connected to the ground. The light emitting diode
124
of the photocoupler
123
has the anode and cathode thereof connected to the D point and the output terminal of the differential amplifier
121
, respectively. The phototransistor
125
of the photocoupler
123
has the emitter and collector thereof connected to the ground and PWM circuit
116
, respectively.
The differential amplifier
121
is supplied at the inverting input terminal thereof with a DC voltage (V
P
) produced by dividing the DC voltage (V
P
) at the D point at a ratio of voltage division between the voltage dividers
119
and
120
. Also, the differential amplifier
121
is supplied at the non-inverting input terminal thereof with a reference voltage (V
ref
) generated by the reference voltage source
122
. The differential amplifier
121
amplifies a difference in voltage between the non-inverting and inverting input terminals thereof to provide a difference voltage, namely, an error voltage, between the voltage-divided DC voltage (V
P
) and reference voltage (V
ref
). The error voltage is applied to the PWM circuit
116
via the photocoupler
123
. The PWM circuit
116
varies, based on the error voltage, the duty ratio of the PWM signal and switches the switching element
115
such that the DC voltage (V
P
) at the D point is stabilized at a constant level.
The first switching converter
101
further includes a reverse flow-preventive diode
126
, an output resistor
127
, a positive output terminal
128
and a negative output terminal
129
. The reverse flow-preventive diode
126
has the anode thereof connected to the D point and the cathode thereof connected to the positive output terminal
128
via the output resistor
127
. The negative output terminal
129
is connected to the ground.
The conventional power supply system
100
has the first and second switching converters
101
and
102
connected in parallel to each other, and supplies the load
103
with a power.
More specifically, the positive output terminal
128
of the first switching converter
101
and the positive output terminal
128
of the second switching converter
102
are connected to each other and to the positive power input terminal
104
of the load
103
. Furthermore, the negative output terminal
129
of the first switching converter
101
and the negative output terminal
129
of the second switching converter
102
are connected to each other and to the negative power input terminal
105
of the load
103
.
As in the above, the conventional power supply system
100
supplies the load
103
with a power which is larger than that generated by one switching converter.
Generally, in case a plurality of power supply apparatuses are connected in parallel to each other, there takes place a very small difference in output voltage between the power supply apparatuses.
Thus, in the conventional power supply system
100
, the reverse flow-preventive diode
126
is provided to prevent a current from flowing from the switching converter which generates a high voltage to the switching converter which generates a low voltage, and the output resistor
127
is provided to absorb the potential difference, to minimize the difference between the currents supplied from the two switching converters
101
and
102
, respectively, to the load
103
and to supply a power to the load
103
very efficiently.
It is assumed now that the voltage (V
P
) generated at the D point of the first switching converter
101
has a value V
P1
voltage (V
P
) gen
Sasaki Masayoshi
Umetsu Koji
Kananen, Esq. Ronald P.
Laxton Gary L.
Rader Fishman & Grauer PLLC.
Sony Corporation
Sterrett Jeffrey
LandOfFree
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