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Dynamic behavior of selected SiC and
QspeedTM diodes and their comparisons in
various practical applications
P.Spanik IEEE Member, M. Frivaldsky IEEE Member, Roman Radvan, Marek Valco
University of Zilina, Faculty of electrical engineering, Department of mechatronics and electronics
Univerzitna 1, SK010 26 Zilina, Slovakia
michal.frivaldsky@fel.uniza.sk
Abstract - This paper deals with investigation of dynamic
behavior of perspective power diode structures. Main scope
is research of impact of diode's dynamics on the efficiency of
switched mode power supply suited for dedicated
application. In principle, the investigation of dynamic
behavior was made in order to find out dependence of diode
losses on the switching frequency and supply voltage.
Quantification of received data was based on experimental
measurements and consequently was converted into
continuous form for graphic interpretation. We have focused
on diode structures which today present most innovative
solution for high frequency applications. It deals about
comparisons of standard Si schottky diode MBR20200CT,
SiC diodes SDT10S30, SDT12S60, C4D15120 and highest
performance Si diodes - QSpeed products QH12TZ600,
LQA12P300. As a merit of performance, each diode has been
utilized in proposed converters - LLC converter and PFC
converter, whereby efficiency of each converter has been
investigated and plotted in the dependency of utilized
rectifier.
Keywords-diode, reverse recovery, efficiency, switching
losses
I. INTRODUCTION
In most of practical applications of power electronics
losses caused by diode’s turn – off process forms
significant part of total losses of power semiconductor
system. The goal of every power semiconductor system
design is approach to the highest efficiency with respect to
maximum output power. However, different practical
applications are requiring utilization of different circuit
topology, in which projection and selection of proper
components are performing the most important challenge
at gaining of optimal power. Almost all Switched – Mode
Power Supplies (SMPS) are nowadays being developed in
cooperation with a power factor correction (PFC) input
stage in order to meet the international regulatory
standards for harmonic content[1].
Together with the development in the field of switched
model power supplies, the practical use of resonant
topologies is being more and more significant. Current
tendencies are characterized by continuous increase of
efficiency (reducing switching losses) and increase of
power density (decreasing volume). The LLC resonant
converter is nowadays a very popular solution for most of
consumer and/or industrial applications.
Altogether with previous description the performance in
dependency on cost is almost very important and mostly
limiting factor for innovative practical designs. Due to that,
we have provided research of dynamic properties of most
perspective diode structures which are nowadays available
for practical use in PFC and LLC converter circuits [2] [3].
In the first part of this paper, the description of SiC and
Qspeed structures is made. After that, the investigation of
dynamic properties of selected diode in dependency on
various circuit parameter in hard switching mode is being
shown. Finally utilization of selected diodes in proposed
PFC and LLC converter is made, whereby influence of
diode on the efficiency of converter was discovered [4] [5].
II. PROPERTIES OF DIODES
Like any other semiconductors diode is not an ideal
device. If the diode selection is incorrect for given
application, then the diode parameters can increase the turn
– on losses of power transistor (MOSFET, IGBT) and even
for the diode itself. Singularity of application areas leads to
the development of various diode technologies of which
every have its specific abilities:
- Low VF with high Qrr and trr
- Moderate VF and moderate trr
- High VF and low trr
The mentioned development brings some types of
special diodes; those behaviors could eliminate
unacceptable effects during active or passive mode of
device.
SBD - Schottky Barier Diode – this type of diode
utilizes metal – semiconductor rectifying junction. The
differences from PN junction are better dynamics – caused
Fig. 1. Interleaved PFC circuit and LLC circuit
by the existence of s.c. hot electrons, those life time is
from 10-11 to 10-13, that is 106 times less than with
classic PN diodes. This warrants almost zero – recovery
time [9]. According to present development in the field of
power electronics, standard Schottky barrier rectifiers
based on silicon substrate had reached their threshold
limits (reverse recovery time, reverse voltage, reverse
recovery charge). Present development in the field of
material engineering expects elimination of mentioned
limitations by implementation of new progressive
materials (silicon carbide - SiC diodes), or by combination
of both Schottky and PN junction in the same device. In
the next subchapter, both structures will be shortly
introduced.
A. SiC diodes
It is possible to avoid switching losses given with Qrr by
using 600V SiC Schottky diode witch haven’t reverse
recovery effect but their losses are related to capacitance
reverse current peak in simplicity. A Solution combine
good properties of PN and Schottky diode was developed
recently and is called Merged-Structure. Both devices are
connected together with low impedance p regions to the
anode of the device (Fig. x1). This concept used
advantages of the wide bandgap potential of SiC, witch
under normal conditions have relatively high junction
voltage (3-4V). This fact prevents conduction of PN
structure. In overload conditions the forward drop of
Schottky diode will rise to value of junction voltage so PN
structure provides hole-carrier injection for conductivity
modulation in the drift region. Task of p bodies is
concentrating the maximum electric field away from
Schottky barrier surface. This allows working with higher
blocking voltage and another advantage is higher
ruggedness of device. Due to the material characteristics of
the SiC and other facts is reverse recovery charge is
essentially unmeasurable. In basics, connecting these two
diodes together should result in the lower forward
dissipation of the Schottky at current levels up to a few
times the rated forward current of the diode, with the large
overload capability and higher peak current of the PN
structure.
Fig. 2. The structures of SiC diodes, top (convetntional), bottom
(merged)
B. QspeedTM diodes
Qspeed diode is a patented device design and processes
to create the highest performance Si based rectifier. They
are developed in order to give best performance to cost
ratio. The basic structure of the diode is called "merged PN
Schottky (MPS)". From that it is clear that it combines
both schottky and PN junction in the same device. Such
structure combines best of each structure, low VF / High
speed Schottky and low leakage / High blocking P-N
junction. Finally due to deep trench technology, through
which implementation of P-wells is made, provide
conductivity modulation efficiently in bulk material what
results in less hole injection = low Qrr.
III. PARAMETRICAL EXPERIMENTAL INVESTIGATION
OF DYNAMIC PROPERTIES OF SELECTED DIODES
The experimental measurements required construction
of testing circuit, which enabled to change the power
circuit parameters just to reach the conditions in practical
application (supply voltage, switching frequency, and load
current). This led us to construct a testing device, whose
construction is realized as circuit with variable topology
whereby primary requirement was to gain exact emulation
of different soft – switching techniques and consecutive
interpretation of generated switching loss [5] [6].
For the purposes of experimental verification we have
focused namely on these devices:
Note: parameters are valid for 25 ºC.
TABLE I
TYPES OF INVESTIGATED DIODES
IF(AV)
[A]
VRRM
[V]
I RM(t yp)
[mA]
V F(max)
[V]
TRR(max)
[ns]
MBR20200CT 20 200 1 1 n.a
LQA12T300C 6 300 1,6 1,9 11,5
QH12TZ600 12 600 1,8 3,1 11,6
SDT10S30 10 300 n.a. 1,7 n.a.
SDT12S60 12 600 n.a. 1,7 n.a
It can be seen that we have focused on the structures,
whose current and voltage ratings are according to the
possibilities as closest as possible. Investigation of
dynamic behavior was done with the use of well-known
circuit, which is shown on fig. 3. This circuit is generally
known as testing configuration for investigation of
dynamics of the power diodes as well as of the power
transistors. Due to fact, that our aim is comparison of
today's top class devices, we have utilized IPW60R070C6
as power transistor.
Fig. 3. Waveform of diode's current during turn-off process
Several measurements were realized under change of
parameters, by which the diode turn - off losses are
dependent on (switching frequency, supply voltage, load
current).
In order to evaluate measured results we have used
discrete forms of equation (3). The measured data were
processed in the table editor and consequently evaluated.
The turn-off losses are generated during reverse recovery
time of the diode, whereby this interval is :
t
R
R = tA + t
B
(1)
Fig. 4. Waveform of diode's current during turn-off process
, whereby for the power loss calculation the next
equation is valid:
onon W
T
P1
= (2)
() ()
∫⋅⋅= dttutiW PPon (3)
T – time - period of computed action
iP – time function of device’s current
uP – time function of device’s voltage
Most of data that are available from oscilloscope for
calculation are in discrete form, so then it is necessary to
use equations in discrete version (4), instead of (3).
[] []
TnUnIW
Z
Z
T
Tn
PPon Δ⋅⋅= ∑
=
2
1
(4)
, where
TZ1 – is sequence of sample at the begin of process
(turn – on/off, stabilized conductivity/non-conductivity of
device)
TZ2 – is sequence of sample at the end of process
(turn – on/off, stabilize conductivity/non-conductivity of
device)
IP[n] – i-sample of current through device
UP[n] – i-sample of device’s voltage
ΔT – sampling time
Thereby it is possible to calculate the element of energy
which is being absorbed by diode during time - interval trr.
Consequently there is need to use an equation to determine
the value of total losses:
onon W
T
P1
=
Based on such analysis it is possible to select most
suitable diode for the application with given circuit
parameters (load current, switching frequency, etc...).
IV. EVALUATION OF THE DYNAMIC BEHAVIOUR
As was mentioned, the experimental investigation was
done during change of parameters which are influencing
diode´s dynamic properties in the highest amount.These
were:
- diode current IF(AV) - 5 A
- diode reverse voltage UR - from 50 V up to 300 V
- switching frequency fSW - from 50 kHz up to 300 kHz
The evaluation of switching losses is done through 3-D
graphical interpretation.
C. MBR20200CT
50 100 150 200
50
150
250
0
0.5
1
1.5
2
2.5
3
Ploss (W)
voltage (V)
fsw (kHz)
2.5-3
2-2.5
1.5-2
1-1.5
0.5-1
0-0.5
Fig. 5. 3D graphical interpretation of turn-off losses for MBR20200CT
D. LQA12T300
50 100 150 200 250 300
50
200
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
Ploss (W)
voltag e (V )
fsw
(kHz)
0.45-0.5
0.4-0.45
0.35-0.4
0.3-0.35
0.25-0.3
0.2-0.25
0.15-0.2
0.1-0.15
0.05-0.1
0-0.05
Fig. 6. 3D graphical interpretation of turn-off losses for LQA12T300
E. QH12TZ600
50 100 150 200 250 300
50
150
250
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Ploss (W)
voltage (V)
fsw
(kHz)
0.8-0.9
0.7-0.8
0.6-0.7
0.5-0.6
0.4-0.5
0.3-0.4
0.2-0.3
0.1-0.2
0-0.1
Fig. 7. 3D graphical interpretation of turn-off losses for QH12TZ600
F. SDT10S30
50 100 150 200 250 300
50
150
250
0
0.5
1
1.5
2
2.5
3
Ploss (W)
voltag e (V)
fsw (kHz)
2.5-3
2-2.5
1.5-2
1-1.5
0.5-1
0-0.5
Fig. 8. 3D graphical interpretation of turn-off losses for SDT10S30
G. SDT12S60
50 100 150 200 250 300
50
150
250
0
0.5
1
1.5
2
2.5
Ploss (W)
voltage (V)
fsw
(kHz)
2-2.5
1.5-2
1-1.5
0.5-1
0-0.5
Fig. 9. 3D graphical interpretation of turn-off losses for SDT12S60
Parametrical investigation of turn-off loss generation
shows exponential dependency on the applied voltage and
almost linear dependency on the switching frequency. The
lowest losses had occurred during investigation of Qspeed
structure LQA12T300. It has very low losses in whole
range of investigated parameters, whereby its dependency
on switching frequency can be almost neglected. Second
diode which has showed best performance is second type
of Qspeed diode QH12TZ600. Standard Schottky diode
MBR20200CT together with both SiC structures
SDT10S30 and SDT12S60 are showing similar
performace. The only disadvantage of MBR20200CT is
that its reverse voltage can be only up to 200 V. On the
other side, SDT12S60 shows higher dependency on
switching frequency against other structures, what can be
caused due to higher value of internal capacitances, which
are influencing turn-off process of diode. Diode
LQA12T300C are the highest performance 300 V diodes
available. Manufacturer declares soft switching of this
diode with dramatically reduced overshoot and EMI. With
such structure, the elimination of snubber circuit can be
easily done. All these facts are confirmed by best
performance from all of the investigated structures. Also
QH12TZ600 is diode, which is suited for applications
with switching frequencies above 80 kHz what is
perfectly confirmed also by these experiments.
In next chapter we are evaluating behavior of each
diode in dedicated applications, i.e. in selected topologies
of switched mode power supplies.
V. UTILIZATION IN DEDICATED APPLICATIONS
TARGETING HIGHEST EFFICIENCY
As was mentioned in the introduction of this paper,
different practical applications are requiring utilization of
different circuit topology, in which projection and
selection of proper components are performing the most
important challenge at gaining of optimal ratio between
performance and cost [6] [7] [8] [9] [10]. The utilization
of selected diodes was done in proposed PFC and LLC
converters, whereby influence of diode behavior on the
efficiency of converter has been discovering.
H. Investigation of performance in the case of LLC
converter
The LLC converter became very popular solution of
SMPS almost in every industrial and consumer area. The
main parameters of proposed LLC converter are:
- input voltage: 320 Vdc - 400 Vdc
- output voltage: 24 Vdc
- output power: 450 W
- switching frequency (resonant): 100 kHz
Diodes which hava been selected for investigation were:
- LAQ12T300C, MBR20200CT, SDT10S30
That means, that each of the structure (standard Schottky,
Qspeed, and SiC) have undergone experiments, which
have been provided in the way of evaluation of efficiency
in the whole range of power loading of proposed
converter, at nominal value of input voltage (400 Vdc).
Next figure (fig.10) is showing waveforms of efficiency
in dependency on output power. The measurements were
provided for each diode at 25 ºC.
Fig. 10. Efficiency of LLC converter for various types of diode in
dependency on output power (W)
Evaluation of results shows that highest efficiency has
been achieved during utilization of the MBR20200CT.
SiC diode is in comparisson with other types the worsest
solution for such applications. The best performance of
MBR20200CT is caused due to the lowest value of
forward voltage VF, which in connection with high peak
value of diode current and due to its sinusoidal waveform
reduces condution losses of diode. Lower efficiency in the
case of LQA12T300C and SDT10S30 is caused almost
due to higher value of VF and thus due to higher condution
losses.
40%
50%
60%
70%
80%
90%
100%
0 50 100 150 200 250 300 350 400 450 500
MBR20200CT LQA12P300 SDT10S30
I. Investigation of performance in the case of PFC
converter
Second proposed converter is PFC converter in boost
configuration (fig.11). The main parameters of proposed
PFC converter are:
- input voltage: 85 Vac - 230 Vac
- output voltage: 400 Vdc ± 2%
- output power: 1 kW
- switching frequency: 100 kHz
Diodes which hava been selected for investigation were:
- QH12TZ600, D12S600, C4D15120
It can be seen that during this experiment we had to
focus on diodes with higher blocking voltage, and thus
standard Schottky diode MBR20200CT was not able to be
utilized. In first case it deals about Qspeed structure, and
two other diodes are SiC, whereby the last C4D15120
presents last family from Infineon SiC diodes.
Fig. 11. PFC converter in BOOST configuration
As in previous case, investigated parameter was
efficiency of proposed PFC converter in wider power
range. Next figure (fig.11) is showing waveforms of
efficiency in dependency on output power. The
measurements were provided for each diode at 25 ºC and
at 230 Vac. Fig. 12 shows evaluation of measurement
results at 25 ºC and 85 Vac
Both experiments on PFC circuit are showing that
performance of utilized diodes is very similar. Very small
deviations occured during low power loading in the case
of C4D15120. It has to be said that this diode presents
device, which is suited for high-performance applications.
But main result of this experiment was investigation of
dynamic properties of Qspeed diodes and consequent
comparisson against SiC structure. As can be see, the
performance of Qspeed is similar to SiC even its cost is
much lower (fig.14).
Fig. 12. Efficiency of PFC converter for various types of diode in
dependency on output power (W) at 230 Vac of input voltage
Fig. 13. Efficiency of PFC converter for various types of diode on output
power (W) at 85 Vac of input voltage
Fig. 14. Interpretation of "VALUE" of diodes based on various
technology principle
VI. CONCLUSION
The parametrical measurements have demonstrated
massive influence of circuit parameters on diode's turn-off
losses. These experiments have discovered dynamic
properties of selected diode structure and with the use of
results in graphical interpretation it is possible to check
turn-of losses as well as other part of losses and thus to
realize proper dimensioning of final power electronic
system. Aim of this work was to investigate in which
manner is this dynamic behavior influencing performance
of proposed electrical circuits. As was discovered, the
price and performance of dedicated device can not be
always suitable for each application as well as diodes with
lower cost can achieve performance of that which are
acting as top level class devices. Designers versed in the
subtle performance of trade-offs and parasitic of the new
diodes can optimize circuit efficiency and/or achieving
meaningful reductions in overall system cost, size, weight
and complexity [14] [15] [16]..
ACKNOWLEDGEMENT
The authors wish to thank to Slovak grant agency
APVV for project no. LPP-0366-09, and to Slovak grant
agency VEGA for project no. 1/0943/11. Next to to R&D
operational program Centre of excellence of power
electronics systems and materials for their components
No. ITMS 2622012003.
89.00%
89.50%
90.00%
90.50%
91.00%
91.50%
92.00%
92.50%
93.00%
0 50 100 150 200 250 300 350 400 450 50
0
QH12T Z600 D12S600 C4D15120
EMI filter
Rectif ier
LD
C
+
T
+
-
AC Input
DC Output
PFC controller
87.00%
87.50%
88.00%
88.50%
89.00%
89.50%
90.00%
90.50%
91
.
00%
0 50 100 150 200 25 0 300 350 400 450
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