Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2002-02-28
2003-04-15
Sterrett, Jeffrey (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
Reexamination Certificate
active
06549432
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to multiple-output, off-line power converters, and more particularly to multiple-output, single winding, bi-directional flyback converters.
BACKGROUND OF THE INVENTION
There are increasing demands in the electronic industry for power supplies that provide multiple regulated outputs. With various integrated circuits and electronic devices operating at different voltages, the ability to supply efficiently regulated multiple voltage outputs from a single power supply has become increasingly more important.
Flyback converters constitute an economically advantageous solution to implement off-line power supplies with multiple outputs. The principle of bi-directional flyback is well known. Bi-directional flyback was first used in uninterrupted power supplies (UPS) where a bi-directional flyback would charge a battery most of the time, i.e., energy flowing into the battery. When the input power source is interrupted, the energy then flows out of the battery and into the load.
FIG. 1
illustrates a known flyback converter. The flyback converter is comprised of a power supply
102
, a transformer
103
with a primary winding
104
and a plurality of secondary windings
106
,
112
,
114
, one for each voltage output, a power supply controller
108
, an input switch
110
and post regulators
116
,
118
. In this example, the flyback implementation uses a single switch
110
on the primary side of the transformer
103
to directly regulate the output voltage V
A
. The cross-regulation of the rest of the output voltages is achieved by the turns ratio of the secondary windings
112
and
114
. However, the presence of leakage inductance and other parasitics results in wide tolerances for the cross-regulated outputs, which do not satisfy strict regulation requirements. The post regulators
116
and
118
are thus necessary to improve the regulation of the output voltages. However, this approach increases the cost and reduces the efficiency of the power supply.
Recently secondary-side control methods have been proposed in European Patent Nos. 0 698 959 and 0 772 284 and U.S. Pat. No. 5,617,015, which include switches on the secondary side of the transformer. The switches on the secondary side of the transformer are used to provide independently regulated outputs, which operate over universal mains voltage and wide load variations. The value of each voltage output can be independently set at different levels by the controller without modification of the circuit.
In European Patent No. 0 698 959, as illustrated in
FIG. 2
, a separate secondary-side winding
210
,
212
,
214
is used to generate each output voltage V
1
, V
2
, V
3
, respectively. A rectifying diode
216
,
218
,
220
is connected in series with each secondary winding
210
,
212
,
214
, respectively. A semiconductor power switch
222
,
224
is connected in series with all but the first secondary winding
210
. A regulator RS
1
of the first output circuit controls the regulator RS
0
of the primary side circuit
202
. Output regulators RS
2
and RS
3
control the secondary side switches
222
and
224
, respectively. The input dc voltage V
IN
, a voltage representation of the primary side switch
204
and the output of one of the regulators are also fed to the primary side regulator RS
0
.
European Patent No. 0 772 284 describes a different secondary-side control method where one secondary winding supplies multiple output voltages via separate branches as illustrated in FIG.
3
. Each output voltage V
1
, V
2
, V
3
is rectified by a diode
302
,
304
,
306
. The first output V
1
is regulated by the pulse width of the primary-side switch
308
. A switch
310
,
312
, is inserted in series into each branch supplying the rest of the output voltages V
2
, V
3
. A regulator
314
and
316
senses each of the output voltages V
2
, V
3
and controls the duty cycle of the corresponding switch to regulate the output voltage.
U.S. Pat. No. 5,617,015 describes a voltage regulator providing multiple independently regulated outputs as illustrated in
FIG. 4. A
dedicated switch
402
,
404
,
406
for each output voltage V
1
, V
2
, V
3
controls the energy delivered to the output. Energy is delivered to the outputs that have fallen below the lower limit of an acceptable range. A voltage regulator
408
stops supplying the outputs that have exceeded the upper limit of the acceptable range. The input switch
410
directly regulates the output connected to the output switch
402
,
404
,
406
which is turned on last in the switching sequence.
As noted above, the above-described methods control the on and off state of the primary-side switch based on the values of the output voltages. However, these methods result in hard switching of the primary-side switch which increases the switching losses and reduces the efficiency of the power converter. Thus, there is a need for a bi-directional flyback converter which reduces switching losses by preventing hard switching of the primary-side switch.
SUMMARY OF THE INVENTION
It is an object of the invention to overcome the above-described deficiencies of the known flyback converters by providing a multiple-output, bi-directional flyback converter with soft switching of the input switch.
According to one embodiment of the invention, a bi-directional flyback converter is disclosed. The primary-side of the converter is comprised of an input power supply, a transformer with a primary winding and a secondary winding, and an input switch with an associated diode, wherein a first end of the primary winding is connected to the input power supply and a second end of the primary winding is connected to the input switch. A first predetermined number of output voltage circuits are connected to the secondary winding each producing an output voltage. Each output voltage circuit has an output switch with an associated diode, and a diode connected in series between the output voltage switch and the secondary winding. A last output voltage circuit with a bi-directional switch and associated diode is connected connection to the secondary winding. A control unit controls the switching of the input switch, the predetermined number of output switches and the bi-directional switch, wherein the switching of the bi-directional switch is controlled so as to allow for soft switching of the input switch.
According to another embodiment of the invention, a bi-directional flyback converter is disclosed. The primary-side of the converter is comprised of an input power supply, a transformer with a primary winding and a secondary winding, and an input switch with an associated diode, wherein a first end of the primary winding is connected to the input power supply and a second end of the primary winding is connected to the input switch. A first predetermined number of output voltage circuits are connected to a separate secondary winding each producing an output voltage. Each output voltage circuit has an output switch with an associated diode, and a diode connected in series between the output voltage switch and the secondary winding. A last output voltage circuit with a bi-directional switch and associated diode is connected connection to a separate secondary winding. A control unit controls the switching of the input switch, the predetermined number of output switches and the bi-directional switch, wherein the switching of the bi-directional switch is controlled so as to allow for soft switching of the input switch.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereafter.
REFERENCES:
patent: 4847742 (1989-07-01), Ohashi et al.
patent: 5617015 (1997-04-01), Goder et al.
patent: 5663874 (1997-09-01), Mader et al.
patent: 6330169 (2001-12-01), Mullett et al.
patent: 698959 (1996-02-01), None
patent: 772284 (1997-05-01), None
Bourdillon Laurence
Giannopoulos Demetri
Lee Nai-Chi
Goodman Edward W.
Koninklijke Philips Electronics , N.V.
Sterrett Jeffrey
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