07-02-2012, 11:52 AM
Evaluation of AC VRM Topologies for High-Frequency Power Distribution Systems
[attachment=17228]
I. INTRODUCTION
Today’s high-speed microprocessors represent highly
dynamic power loads that necessitate the use of distributed
power architectures. Typically, these distributed powerdelivery
systems use a conventional multiple-output “silver
box” as a front end to supply power directly to “not-sodynamic”
loads (e.g., disk drives) and to generate a dc bus for
distribution to the dc/dc point-of-load regulators that are used
for powering the processors. Generally, these point-of-load
regulators, also known as voltage regulator modules (VRMs),
are located very close to the processors to minimize the
interconnect inductance so that the desired transient response
of the VRMs is obtained with a minimal decoupling
capacitance [1].
II. HF AC VRM TOPOLOGIES
Generally, the conventional full-wave rectifier with
voltage-type load (also called peak-detection rectifier), shown
in Fig. 1, is not suitable for the HF sinusoidal ac VRMs
because of its poor power factor and high current harmonics.
The conventional full-wave rectifier with current-type load,
shown in Fig. 2, has better power factor than the rectifier with
voltage-type load. Ideally, the input current of the circuit in
Fig. 2 has rectangular waveform and is in phase with the
input voltage, resulting in a theoretical maximum power
factor equal to 0.9 [12].
III. SRR WITH VARIABLE CAPACITANCE
Control characteristics of the regulated SRR with variable
resonant capacitance can be obtained using the sinusoidal
(fundamental) approximation method [12], which simplifies
the SRR to the circuit shown in Fig. 5, where Lm is the
magnetizing inductance of the transformer. In Fig. 5, it is
assumed that the leakage inductance of the transformer is
lumped with the resonant inductance Lr. If the ac-bus voltage
is defined as
vin = Vin,pk × sin(wint) ,
IV. SPRR WITH VARIABLE CAPACITANCE
Applying the sinusoidal (fundamental) approximation
method [12] to the SPRR in Fig. 4, the equivalent circuit
shown in Fig. 8 is obtained, where the equivalent load
resistance is defined as
COMPARISON OF AC VRM TOPOLOGIES
A comparison of the proposed resonant rectifier topologies
for ac VRMs is presented in Table I. Table I lists the
normalized turns ratio of the transformer, the normalized rms
currents of the transformer primary and secondary windings,
and the normalized current and voltage stresses of the
synchronous rectifiers. For simplicity, it was assumed that all
components are ideal. As can be seen from Table I, the
SPRR with CDR has the smallest current stress in the
secondary winding, while the SRR has the smallest current
stress in the primary winding. The synchronous rectifiers in
the SPRR have smaller current stress but larger voltage stress
than in the SRR.
[attachment=17228]
I. INTRODUCTION
Today’s high-speed microprocessors represent highly
dynamic power loads that necessitate the use of distributed
power architectures. Typically, these distributed powerdelivery
systems use a conventional multiple-output “silver
box” as a front end to supply power directly to “not-sodynamic”
loads (e.g., disk drives) and to generate a dc bus for
distribution to the dc/dc point-of-load regulators that are used
for powering the processors. Generally, these point-of-load
regulators, also known as voltage regulator modules (VRMs),
are located very close to the processors to minimize the
interconnect inductance so that the desired transient response
of the VRMs is obtained with a minimal decoupling
capacitance [1].
II. HF AC VRM TOPOLOGIES
Generally, the conventional full-wave rectifier with
voltage-type load (also called peak-detection rectifier), shown
in Fig. 1, is not suitable for the HF sinusoidal ac VRMs
because of its poor power factor and high current harmonics.
The conventional full-wave rectifier with current-type load,
shown in Fig. 2, has better power factor than the rectifier with
voltage-type load. Ideally, the input current of the circuit in
Fig. 2 has rectangular waveform and is in phase with the
input voltage, resulting in a theoretical maximum power
factor equal to 0.9 [12].
III. SRR WITH VARIABLE CAPACITANCE
Control characteristics of the regulated SRR with variable
resonant capacitance can be obtained using the sinusoidal
(fundamental) approximation method [12], which simplifies
the SRR to the circuit shown in Fig. 5, where Lm is the
magnetizing inductance of the transformer. In Fig. 5, it is
assumed that the leakage inductance of the transformer is
lumped with the resonant inductance Lr. If the ac-bus voltage
is defined as
vin = Vin,pk × sin(wint) ,
IV. SPRR WITH VARIABLE CAPACITANCE
Applying the sinusoidal (fundamental) approximation
method [12] to the SPRR in Fig. 4, the equivalent circuit
shown in Fig. 8 is obtained, where the equivalent load
resistance is defined as
COMPARISON OF AC VRM TOPOLOGIES
A comparison of the proposed resonant rectifier topologies
for ac VRMs is presented in Table I. Table I lists the
normalized turns ratio of the transformer, the normalized rms
currents of the transformer primary and secondary windings,
and the normalized current and voltage stresses of the
synchronous rectifiers. For simplicity, it was assumed that all
components are ideal. As can be seen from Table I, the
SPRR with CDR has the smallest current stress in the
secondary winding, while the SRR has the smallest current
stress in the primary winding. The synchronous rectifiers in
the SPRR have smaller current stress but larger voltage stress
than in the SRR.