Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Reexamination Certificate
2001-07-23
2003-02-11
Sherry, Michael (Department: 2838)
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
C363S132000, C327S423000, C327S588000
Reexamination Certificate
active
06519168
ABSTRACT:
TECHNICAL FIELD
This invention relates to power supplies for electronic equipment and, in particular, to inverters for generating high frequency sinusoidal AC voltages for electronics equipment used in telecommunications and computer systems. Typical examples of potential use are in personal computers, servers, routers, network processors, and opto-electronic equipment.
BACKGROUND OF THE INVENTION
Segments of the personal computer (PC) industry have dramatically changed during the last decade. The future is even more challenging. A dramatic increase in the processor speeds of PCs has required an overwhelming increase in current and associated dynamics (very high slew rate). This already challenging technical requirement is further complicated by a need for voltage reduction, potentially to sub-volt levels.
In the past, there was virtually no challenge in powering computers. A multiple output, very slow power supply called a “Silver Box (SB)” was adapted to meet the requirements of every power demand. However, as silicon development progressed, multiple voltages of less than 3.3V were required. Voltage Regulator Modules (VRMs) on the processor Mother Board (MB) were a logical solution to that problem. Today, the number of VRMs required on the Mother Board is increasing. In addition to the VRMs, a large number of de-coupling capacitors are required in proximity of the processor to meet the requirements of very high slew rate of the current. This has resulted in a rapid increase in the cost, as well as a large reduction in overall efficiency, of the power delivery system.
A number of options for improving this situation have been explored. For example, Advanced Voltage Regulator Module (AVRM) offers the capability to supply high di/dt and high current, however, at increased cost, and with low efficiency and moderately high capacity of the de-coupling capacitors. Replacing low voltage DC distribution with higher DC voltage, such as 48V, is more promising but has a drawback of higher cost. Recently a novel High Frequency Alternating Current (HFAC) power delivery architecture has been proposed for powering the future generation PCs in reference entitled, “PC Platform Power Distribution System: Past Application, Today's Challenge and Future Direction” published in the conference proceedings of International Telecommunications Energy Conference, Copenhagen, Denmark, June 1999 by J. Drobnik, L. Huang, P. Jain and R. Steigerwald. In the HFAC architecture, the system power supply (silver box) generates high frequency and high voltage. The HFAC is then fed to an individual AC-DC converter (ACVRM) and converted into DC of specific parameters at the point of use.
HFAC is conceptually the simplest architecture proposed to date, which deals with all of the power delivery issues defined above. This includes elimination of duplicated power conversions, and active energy steering without additional components.
The key to successful implementation of an HFAC power delivery system resides in the two stages of power conversion namely; DC to AC high frequency conversion stage and the stage that converts high frequency AC to DC.
FIG. 1
shows a block diagram of a conventional DC to high frequency AC inverter
100
. The inverter
100
includes a full-bridge inverter
104
having an input
104
A for receiving a DC input voltage
102
and providing an output
104
B. The output
104
B is connected at
106
to an input
108
A of a resonant circuit
108
. An output
108
B of the resonant circuit
108
provides a high frequency AC output voltage
110
. The AC output voltage
110
is fed back
112
to an input
114
A of a phase-shift modulation circuit
114
. The modulation circuit provides four outputs
114
B connected at
116
to four inputs
118
A of a gate drive circuit
118
. The gate drive circuit
118
has four outputs
118
B connected at
120
to four inputs
104
C of the inverter
104
.
A number of power circuit configurations to implement the full-bridge inverter and resonant circuit of
FIG. 1
are possible but the circuits as shown in
FIGS. 2A and B
are the circuits most commonly used in these implementations.
FIG. 2A
shows the full-bridge inverter
104
and the resonant circuit
108
sections of a conventional inverter
200
which was described in ‘A 20 kHz Hybrid Resonant Power Source for the Space Station’,
IEEE Trans. on Aerospace and Electronics Systems,
vol. 25, No. Jul. 4, 1989, 491-496 by P. Jain & M. Tanju. The full-bridge inverter
104
includes a first switch
202
, a second switch
204
, a third switch
206
, and a fourth switch
208
. Each switch
202
,
204
,
206
,
208
is preferably an N-channel field-effect transistor (FET). The resonant circuit
108
includes a series resonant circuit
210
, a parallel resonant circuit
212
, and a transformer
214
.
The full-bridge inverter
104
produces a quasi-square voltage at its output
106
, which is controlled using a phase-shift modulation circuit
114
(
FIG. 1
) commonly used in such applications. Both the series
210
and parallel
212
resonant circuits are tuned to an operating frequency of the inverter. Although the resonant circuit
108
produces a regulated sinusoidal voltage at its output
110
, this inverter
200
does not provide zero-voltage switching conditions for at least two of the four switches
202
,
204
,
206
,
208
, which results in higher switching losses at higher operating frequencies. Therefore, the operation of this circuit is limited to lower operating frequencies.
FIG. 2B
shows the full-bridge inverter
104
and the resonant circuit
108
sections of a conventional inverter
250
which was described in ‘Constant frequency resonant DC/DC converter’, U.S. Pat. No. 5,157,593, Oct. 20, 1992 by P. Jain. The full-bridge inverter
104
is identical to the one shown in FIG.
2
A. The resonant circuit
108
includes a series resonant circuit
210
, a parallel resonant circuit
252
, and a transformer
214
.
The full-bridge circuit
104
produces a quasi-square voltage at its output
106
, which is controlled using a phase-shift modulation circuit
114
(
FIG. 1
) commonly used in such applications. In this configuration, the series resonant circuit
210
is tuned to an operating frequency of the inverter
250
while the parallel circuit
252
is tuned at a frequency, which is lower than the operating frequency. Although the resonant circuit
108
produces a regulated sinusoidal voltage at its output
110
and provides zerovoltage switching conditions for all the four switches
202
,
204
,
206
,
208
, the de-tuning of the parallel branch
252
requires the series resonant components
210
and the output transformer
214
to have higher maximum ratings and hence be more expensive.
Another fundamental problem that limits the operation of the inverter circuits of
FIGS. 2A and B
at higher operating frequencies is gate circuit losses of the FETs
202
,
204
,
206
,
208
used in the full-bridge circuit
104
.
FIG. 3
shows a graph
300
of typical gating signals A
1
302
, A
2
304
, B
1
306
, and B
2
308
produced by the phase-shift circuit
114
.
FIG. 4
shows a graph
400
of gate voltage (VgA
1
)
402
, gate current (igA
1
)
404
, instantaneous gate power (pgA
1
)
406
, and average gate power (PgA
1
)
408
for a gate
202
A of the first FET switch
202
. This graph
400
clearly shows that when a rectangular voltage pulse
402
is applied to the gate
202
A of the FET
202
, which has a capacitance, a pulsating current
404
is drawn from this voltage. This causes the power loss
406
in the gate circuit, which is approximately given by Cg*Vg
2
*f
408
(where Cg is gate capacitance; Vg is gate voltage; and, f is the operating frequency). At higher frequency, the gate losses are prohibitively high, which limits the operation of inverter circuits of
FIGS. 2A and B
at very high frequency.
It is clear from the above discussion that the conventional approaches to converting DC to high frequency AC have low conversion efficiency due to high switching losses.
There therefore exists a need for an inverter topolo
Jain Praveen Kumar
Zhang Haibo
ChipPower.com, Inc.
Laxton Gary L.
Renault Ogilvy
Sherry Michael
Wood Max R.
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