Electric power conversion systems – Current conversion – Using semiconductor-type converter
Reexamination Certificate
2002-05-06
2003-11-18
Patel, Rajnikant B. (Department: 2838)
Electric power conversion systems
Current conversion
Using semiconductor-type converter
C363S098000
Reexamination Certificate
active
06650558
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to switched power supplies, and more particularly to full-wave bridge power supplies.
BACKGROUND OF THE INVENTION
Switching power supplies are becoming more popular for various uses, as their sizes decrease and their power-handling capabilities increase. In general, such power supplies are used to convert one direct voltage to another direct voltage, as for example might be the case when using a mains-powered rectified supply at, say, 200 volts, to a thousand or more volts, as might be required by a transmitter arrangement. Switching power supplies can also be used for reducing voltage, as for example by reducing a mains-powered rectified supply at, say, 200 volts, to 5 or 10 volts, as might be required by a computer board. Instead of a mains-powered supply, the source of the direct voltage might be a vehicular battery. The advent of all-electric and hybrid-electric vehicles gives this aspect of switched power supplies the prospect of extensive use.
The need for smaller power converters and lower weight, or, equivalently, higher power-handling capability without an increase in size, tends to drive the design of DC-to-DC converters toward operation at higher frequencies, at which the magnetic components tend to be smaller than at lower frequencies. Unfortunately, this drive toward higher frequencies tends to exacerbate losses which occur in the semiconductor switches of the converter or power supply.
FIG. 1
illustrates one type of prior-art switched power supply or DC-to-DC (DC/DC) converter. In
FIG. 1
, a source of direct voltage is designated
12
. Source
12
connects to a first, second, third, and fourth controllable semiconductor switches
1
,
2
,
3
, and
4
, respectively. In this embodiment, the semiconductor switches are illustrated by a field-effect transistor (FET) symbol, but the switches can be of any type. In
FIG. 1
, controllable semiconductor switch
1
includes a main current-conducting path
1
p
, extending from a source
1
s
to a drain
1
d
. The current flow in the main current-conducting path
1
p
is controlled by the voltage or charge applied to the control electrode, illustrated as a gate
1
g
, all as is well known to those skilled in the art. Another controllable semiconductor switch is illustrated as
2
, and it includes a main current conducting path
2
p
extending between a source
2
s
and a drain
2
d
, all under the control of the charge or voltage applied to a control electrode, illustrated as a gate
2
g
. Additional controllable semiconductor switches are illustrated as
3
and
4
. Switch
3
includes a controllable path
3
p
extending between source
3
s
and drain
3
d
, under the control of a control electrode
3
g
, and switch
4
includes a controllable path
4
p
extending between source
4
s
and drain
4
d
, controlled by a control electrode
4
g.
In the arrangement of
FIG. 1
, the source
1
s
of switch
1
is connected to the drain
3
d
of switch
3
at a first node or tap
16
a
, and that electrode of switch
1
which is remote from the tap
16
a
, namely drain electrode
1
d
, is connected to a first terminal
12
1
of direct voltage source
12
. Also, that electrode of the main current conducting path
3
p
of switch
3
is connected to the other terminal of the direct voltage power source
12
. More particularly, source
3
s
of switch
3
is connected to terminal
12
2
of source
12
. The arrangement of switches
2
and
4
is not dissimilar to that of switches
1
and
2
. More particularly, the source
2
s
of switch
2
is connected to the drain
4
d
of switch
4
at a tap
16
b
. Those main current conducting path electrodes of switches
2
and
4
which are remote from tap
16
b
are connected to the direct voltage power supply. Thus, drain electrode
2
d
of switch
2
is connected to terminal
12
1
of supply
12
, and the source electrode
4
s
of switch
4
is connected to terminal
12
2
of supply
12
. As known to those skilled in the art, there are several ways to control the switching of the various switches of the power supply of
FIG. 1
, so that an alternating voltage appears across taps
16
a
and
16
b
, where the word “across” means that a voltage difference appears “between” the terminals, however the terminals may be physically arranged.
The alternating voltage appearing across the taps
16
a
and
16
b
of the power supply of
FIG. 1
is coupled to the primary winding
14
p
of a transformer arrangement
14
. Transformer arrangement
14
also includes at least one secondary winding, illustrated as a center-tapped secondary winding
14
s
. Winding
14
s
is connected to a rectifier and filter arrangement including diodes or rectifiers designated D
1
and D
2
, and a filter including a series inductor L and a shunt capacitor C. The output direct voltage of the arrangement of
FIG. 1
is a voltage designated V
o
, produced “across” (again, not a term relating to physical location) capacitor C for application to a load, represented by a resistor R.
Those skilled in the art know that there are several ways to control the controllable switches
1
,
2
,
3
, and
4
of
FIG. 1
in order to generate the desired alternating voltage across the primary winding
14
p
of FIG.
1
. These various techniques have various advantages and disadvantages, and some may be more desirable at various states of the technology than others. Some of these techniques are described in U.S. Pat. No. 4,811,184, issued Mar. 7, 1989 in the name of Koninsky et al.; 4,688,165, issue Aug. 18, 1987 in the name of Pruitt; 4,691,270, issued Sep. 1, 1987 in the name of Pruitt; 4,761,722, issued Aug. 2, 1988 in the name of Pruitt; 5,451,962, issued Sep. 19, 1995 in the name of Steigerwald; 5,684,683, issued Nov. 4, 1997 in the name of Divan et al. An article entitled
Design Review:
100 W, 400 kHz,
DC/DC Converter With Current Doubler Synchronous Rectification Achieves
92% Efficiency, by Laszlo Balogh, gives an overview of various types of switch control. One of the types of switch control which is currently advantageous is the phase-shift control, in which the control electrode drive signals are relatively phase shifted so that intervals of conduction of one switch pair of a bridge, such as switch pair
1
,
3
, to apply power to the transformer, are separated by intervals in which another switch pair, such as switch pair
1
,
2
, are conductive, and no power is applied to the transformer.
FIG. 2
a
is a representation of the sequence of states of operation of the converter or power supply of
FIG. 1
following a phase shift control pattern.
FIGS. 2
b
,
2
c
,
2
d
, and
2
e
(
FIGS. 2
a
through
2
e
or
FIGS. 2
a
-
2
e
) are time plots of ON (main current conducting path conductive) and OFF (main current conducting paths nonconducting) times of controllable semiconductor switches
1
,
2
,
3
, and
4
, respectively, of FIG.
1
.
FIG. 2
f
is a time plot
206
of the voltage applied to the primary winding
14
p
of the transformer
14
of
FIG. 1
,
FIG. 2
g
is a time plot of the magnetizing current I
M
in the primary winding
14
p
of transformer
14
of
FIG. 1
in response to the applied voltage of
FIG. 2
f
.
FIG. 2
h
is an amplitude-time plot illustrating the total current in the transformer
14
of
FIG. 1
, including magnetizing current and load current portions; during the first state in the interval t
0
-t
1
, the current is in a first direction, indicated as “upward” in
FIG. 2
h
.
FIG. 2
j
is a plot of the current in filter inductor L of FIG.
1
. The first state illustrated in
FIG. 2
a
is state S1, which extends from time t
0
to a later time t
1
. In state S1, switches
1
and
4
are ON or conducting, as indicated by the logic “high” or “1” level of the gate signals
201
and
204
of
FIGS. 2
b
and
2
e
, respectively. As a consequence, current flows from terminal
12
1
of supply
12
of
FIG. 1
, through the main current carrying path
1
p
of switch
1
, through the primary winding
14
p
of transformer
14
, and through the main current carrying path
Jayakody Uditha
Pacala Viorel Mark
Shahani Sunder
Tsinetakes John
Duane Morris LLP
Lockhead Martin Corporation
Patel Rajnikant B.
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