Application of modern semiconductor
devices from silicon carbide for the construction
of the synchronous rectifiers
Wydział Elektryczny, Politechnika Białostocka ul. Wiejska 45A, 15-351 Białystok,
e-mail: krupa_adam@ymail.com
In low-voltage isolated DC-DC converters, power losses due to the conduction of rectifying devices are significant. Using
synchronous rectifiers instead of the conventional fast recovery diodes is an effective solution to this problem in most topologies.
This paper provides results of computer simulation in PSpice of implementation SiC (silicon-carbide) diode in synchronous
rectifier topology and shows advantages of this solution.
Keywords and phrases: SiC-device, synchronous rectifier, transformer.
Introduction
The emergence of silicon carbide-(SiC) based power
semiconductor switches with their superior features
compared with silicon (Si) based switches has resulted in
substantial improvements in the performance of power
electronics converter systems.
They have close-to-ideal characteristics, lower onresistances (RDSon) and with less reverse recovery current,
than Si devices SiC semiconductors have small switching
losses. Despite the many advantages they have one major
drawback: high conduction voltage drop compare to Si
elements: theoretical about 1–2 V compare to 0,7 V for
diodes.
In this paper is shown that mentioned disadvantage
can be marginalized by applying SiC device (diode) into
by synchronous rectifier topology.
Synchronous rectifier topology
Modern rectifier topologies have advanced control
to ensure their maximum efficiency. Unfortunately,
coupled with extensive control comes greater number
of elements and thus raises the cost of the converter.
In more advanced systems, unfortunately, it is hard
to make a significant simplification without loss of
controllability. However, if we want to limit the number
of elements while maintaining high efficiency,
synchronous rectifiers may be the solution we are looking for.
“A synchronous rectifier is an electronic circuit that
can improve power-conversion efficiency by placing
a low resistance conduction path across the diode rectifier
in a switch-mode rectifier” [2].
In other words, in parallel with the conducting diode
rectifier MOSFET with low Ron resistance is attached.
By using synchronous semiconductor switch the
threshold voltage of the rectifying diode can be eliminated
and the voltage on the conductive diode becomes the
voltage on conductive transistor which is a function of
the RDSon resistance.
The Fig. 1 presents the most simple possible
configuration of the half-wave rectifier, which is the
power source a diode rectifier and resistive load. By using
the isolation transformer and by connecting parallel with
diode MOSFET transistor configurations we obtain the
most simple synchronous rectifier configuration (Fig. 2).
Transistor control pulses are derived from the
secondary winding of the transformer. When diode is
polarized in the direction of conduction in the transistor
gate is given a positive sine-wave.
Electronics and Informational Technologies
Adam Krupa
Applying SiC diode in a synchronous rectifier
topology
In this paragraph we will present the curves of
voltage and current on diodes in both topologies
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Adam Krupa
Fig. 1. Half-wave rectifier circuit.
Fig. 2. Half-wave synchronous rectifier circuit.
mentioned before. We used PSpice computer simulation
software.
The Cree SiC diode CSD01060 will be compared with
Si diode HFA25TB60 and it will be displayed that not
only have we reduced SiC diode voltage drop but we also
reduced the power dissipation in the converter topology.
Figure 3 shows the voltage at the SiC diode rectifier in
its simplest configuration (Fig. 1). We see that during the
conduction state diode voltage is about 1.3 V. In Fig. 4
we see that using synchronous rectifier topology the
voltage drop on diode during conduction is reduced to
about 0,7 V, however the same voltage was received be for
Si diode. The 0,7 V is voltage on conducting MOSFET.
We have overcome the significantly high voltage drop
on SiC device but why using it in synchronous topology
when we could use ordinary rectifier diode and receive
the same result. The answer lies within power dissipation.
Power loss in the Si diode is about 170 W while the
SiC diode is 10 W.
The received scale of losses was small, but it was
associated with pre-defined parameters of the system.
However, if we consider it in the category of percentage
Fig. 3. Voltage on conducting SiC diode in half-wave rectifier.
Fig. 4. Voltage on conducting SiC diode in half-wave synchronous rectifier.
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improvement the 17-fold reduction in losses is not to be
missed.
Of course, the whole circuit would have to be optimized in a real application. Increasing system efficiency,
and the right choice of MOSFET and diode type and
size is crucial to obtain the maximum value of the system
within the requirements of the application. Nevertheless,
it was demonstrated that in synchronous rectifier
topology the one major disadvantage of SiC device,
which is high conduction voltage drop, is marginalized.
Consequently, the power dissipation within conducting
diode can be reduced.
References
[1] Mihaiu, M.I. “Toward the “Ideal Diode” using power
MOSFET in full wave synchronous rectifiers for low
[2]
[3]
[4]
[5]
voltage power supplies”. International Symposium on
Power Electronics, Electrical Drives, Automation and
Motion. Speedam, 2008.
Mihaiu, M.I., and C.A. Valderrama. “The performance
analysis of the synchronous rectifiers”. 6th International
Conference on Electromechanical and Power Systems,
Chisinau, Rep. Moldova. October 4–6, 2007.
Shinohara, S. “Analysis of Power Losses in MOSFET
Synchronous Rectifiers by Using Their Design Parameter”.
Proceedings of International Symposium on Power
Semiconductor Devices & ICs, Kyoto, 1998.
Xiao, L., and R. Oruganti. “Soft Switched PWM DC/
DC converter with synchronous rectifiers”. Centre for
Power Electronics Electrical Engineering Department
National University of Singapore. IEEE, 1996.
Singh, R., and J. Richmond. “SiC Power Schottky Diodes
in Power Factor Correction Circuits”. Cree, Inc.
Application Note.
Electronics and Informational Technologies
Application of modern semiconductor devices from silicon carbide for the construction of the synchronous rectifiers
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