1MHz Self-Driven ZVS Full-Bridge Converter for
48V Power Pods
Yuancheng Ren, Ming Xu, Douglas Sterk and Fred C. Lee
146 Whittemore Hall, Center for Power Electronics Systems
Virginia Polytechnic Institute and State University
Blacksburg VA, 24061
Email: ycren@cpes.vt.edu
Abstract― In this paper, a self-driven zero-voltage-switching
(ZVS) full-bridge converter
*
is proposed. The control strategy is
similar to an asymmetrical control for each leg. Analysis shows
that it can still achieve ZVS for the primary switches.
Furthermore, this control strategy is very convenient to realize
self-driven. A new driver scheme is proposed, which can solve the
transient response problem of the conventional driver scheme.
Compared with the external driver, the self-driven can save
driver loss and synchronous rectifier body diode conduction loss.
Additionally, compared with the level-shifted self-driven concept
for bridge-type symmetrical topologies, its gate signal is very
clean and suitable for high-frequency applications. A 1MHz,
1.2V/70A prototype is built to verify the analysis. Experimental
results show that it can achieve 81.7% efficiency. And there is an
efficiency improvement of 4.7% over conventional phase-shifted
full-bridge converter with an external driver.
Keywords-Zero Voltage Switching (ZVS); Self-driven; DC/DC
Converters;VRMs; Power Pods
I. INTRODUCTION
Most of today’s high-performance microprocessors for
workstations and servers are 64-bit, and their power
consumption is higher than those of the 32-bit microprocessors
such as the Pentium IV and the Xeon. Usually, the server has
several 64-bit microprocessors working together (Fig. 1). So,
compared with the desktop voltage regulator module (VRM),
the server consumes much higher power (around several KW).
As a result, in order to reduce the loss on the bus, the power
architecture of the server or workstation uses a 48V distributed
power system (DPS) instead of the 12V bus in the desktop.
Besides lower loss on the bus, in a high-voltage DPS the
transient response of the load has less effect on the bus voltage,
as well as less effect on the other loads. The input filter size of
the high-input-voltage power pod can be reduced significantly
[1]. Another merit of the 48V-input power pod is that because
transformers are used, the duty cycle can be optimized for
efficiency, ripple-canceling effect and transient by adjusting the
turns ratio.
*
This work was supported by Intel, Texas Instruments, National
Semiconductors, Intersil, TDK, Hitachi, Hipro, Power-One and Delta
Electronics. Also, this work made use of ERC shared facilities supported by
the National Science Foundation under Award Number EEC-9731677.
The development of the server’s power supply, normally
called the power pod, has been driven by the fast development
of microprocessors.
Figure 1. Server power archetecture.
Current Demand for Power Pod
0
20
40
60
80
100
120
140
2000 2001 200 2 2003 2004 2005
Output Current (A)
0
20
40
60
80
100
120
140
160
current slew rate(A/us)
Out put Current Current Slew Rate
Figure 2. Intel CPU roadmap.
Most of today’s server microprocessors operate with voltages
between 1.3 V and 1.8 V and with 100A current. And the
current slew rate during a transition is around 100 A/us (Fig.
2). To further increase the processing speed and decrease the
power consumption, the operating voltages of the next
generation of computer microprocessors will be reduced below
1.0 V (Fig. 2). At the same time, it is expected that these
processors will require much more power and will present even
more dynamic loads than today’s microprocessors. To meet the
stringent transient response requirement and to reduce the
passive component size, the power pod switching frequency
should be pushed to the MHz range. This is a great challenge
for power pod design.
Today’s power pod uses pulse width modulation (PWM)
hard-switching topologies, such as the half bridge [2], push-
pull forward [3], full-bridge, etc. In other work [4], a thorough
comparison is made. The push-pull forward converter with
integrated magnetics shows better performance than other
18010-7803-7754-0/03/$17.00 ©2003 IEEE