JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.14, NO.6, DECEMBER, 2014
http://dx.doi.org/10.5573/JSTS.2014.14.6.697
SiC Based Single Chip Programmable AC to DC
Power Converter
Rajendra Pratap, Vineeta Agarwal, and Ravindra K. S
Abstract—A single chip Programmable AC to DC
Power Converter, consisting of wide band gap SiC
MOSFET and SiC diodes, has been proposed which
converts high frequency ac voltage to a conditioned dc
output voltage at user defined given power level. The
converter has high conversion efficiency because of
negligible reverse recovery current in SiC diode and
SiC MOSFET. High frequency operation reduces the
need of bigger size inductor. Lead inductors are
enough to maintain current continuity. A complete
electrical analysis, die area estimation and thermal
analysis of the converter has been presented. It has
been found that settling time and peak overshoot
voltage across the device has reduced significantly
when SiC devices are used with respect to Si devices.
Reduction in peak overshoot also increases the
converter efficiency. The total package substrate
dimension of the converter circuit is only 5 mm × 5
mm. Thermal analysis performed in the paper shows
that these devices would be very useful for use as
miniaturized power converters for load currents of up
to 5-7 amp, keeping the package thermal conductivity
limitation in mind. The converter is ideal for voltage
requirements for sub-5 V level power supplies for
high temperatures and space electronics systems.
Index Terms— Silicon carbide MOSFET, modelling,
system miniaturization, system package, silicon
carbide diode
Manuscript received Oct. 18, 2013; accepted Nov. 4, 2014
MNNIT Allahabad, India
E-mail : rajendra_pratap@ymail.com
I. INTRODUCTION
Increasing demand for continued miniaturization of
electronic device components in today’s analog/digital
circuits has raised the power supply voltage requirements
to programmable sub-5 V levels with minimized reverse
recovery and forward recovery current. Some of the
specific applications could be as power supply to
industrial electronic circuits used under high temperature
conditions and space applications [1]. Mass production
can trigger SiC manufacturing cost reduction which will
enable its use as common direct plug-n-play power
supply for domestic electronic devices which operate at
5V-10A range. The supply voltage to integrated circuit
devices are provided by alternating current to direct
current AC-DC converters, which convert high frequency
ac voltage to a conditioned dc output voltage at a given
power level [2]. Conventional Low-voltage AC-DC
converters generally consist of a big transformer and
diode bridge rectifier, which is often composed of several
diodes, an inductor and capacitor with a voltage regulator
U1 as shown in Fig. 1 [3-5].
The critical feature of the AC-DC diode converter is its
transformer followed by rectification, which allows large
current to flow only in one direction or for positive phase
of the ac input [6]. The bill of material (BOM) list is high
due to which the complete board size is not less than 2 ×
4 cm. Out of the list of material, transformer consumes
more than 40% of the area and hence is the biggest road
block in miniaturizing the complete supply circuit.
SiC devices have very high material band gap (7eV) as
compared to Si devices (1.1eV). Wide band gap material
such as Silicon Carbide can operate at higher temperature
up to 400°C and has a lower thermal resistance than
698
RAJENDRA PRATAP et al : SIC BASED SINGLE CHIP PROGRAMMABLE AC TO DC
POWER CONVERTER
U1
External
Supply
Load
IN
D1
D2
V1
GND
C3
470mF
D3
OUT
D4
C4
0.1m F
R1
C1
470 pF
C2
100 k
0.1pF
Fig. 1. Conventional rectifier based on AC-to-DC power converter.
Silicon, allowing better cooling [7]. SiC device
technology has entered a new era with the
commercialization and acceptance with 1700V/26A
diodes and 1200V/20A MOSFET available in the
marketplace [8, 9]. These MOSFETs have found
applications in high voltage and high temperature power
circuits. Use of SiC allows miniaturizing complete
solution into a single package [10]. Because of the
requirements of high voltage and current withstanding
devices and high frequency response, single package acto-dc programmable power supply was being built using
transformers earlier. In this paper, the authors have tried
to miniaturize the sub-5V DC supply circuits by
resolving some of the conventional circuit issues like
requirement of transformer, heat dissipation and overall
operational efficiency of the circuit elements. SiC based
device selection is helping by allowing to directly
connect high voltage AC sources to the circuit with much
better peak performance of the elements as compared to
their Si counterparts. For the first time, theoretical
analysis and feasibility of single integrated circuit
package arrangement of SiC diode based on high voltage
ac supply full bridge rectifiers followed by SiC MOSFET
based on buck converter, to achieve single package ac-todc power supply is demonstrated. The key benefits are :
system miniaturization which means much smaller board
size (has become possible due to the availability of
miniaturized bare die SiC devices), high efficiency
operation due to zero reverse recovery and zero forward
recovery currents of SiC devices, no requirement of
bulky inductors due to high frequency switching possible
with SiC devices and highly programmable system
because of the MOSFET gate triggering control it
provides to its users.
II. PROPOSED CONVERTER SYSTEM
Fig. 2 shows the proposed AC to DC converter circuit
in its simplest form. The circuit consists of four SiC
diodes D1 to D4 connected in full wave rectifier
configuration. Because of their capability to withstand
high voltage, they are directly being used to rectify the
AC power supply into high voltage DC which is then
being filtered using two on-board electrolytic capacitors.
The SiC MOSFET, MOS1 and diode D5 are being used
in buck-converter configuration to reduce the voltage to
sub-5V externally programmable DC ranges [11].
Inductor L1 is included which is due to component
bonding and package leads. The parasitic extraction of
the device package shows it to be in the range of 5nH to
15nH which is sufficient to sustain the continuity of the
DC current required at the output because SiC MOSFETs
are capable of switching at very high frequencies. The
total gate charge of SiC MOSFET is 47.1 nC which helps
in achieving almost zero forward recovery and reverse
recovery current when SiC MOSFET is switching from
ON to OFF and again ON state. As per datasheet the SiC
MOSFET is capable of switching at approximately
maximum of 4MHz range with rise time of 14 ns and fall
time of 37 ns, turn on delay of 7ns, turn off delay of 46ns
and reverse recovery time of 138ns. The die dimensions
of SiC MOSFET are 3.1mm x 3.1mm. The SiC diodes on
the other hand have zero reverse recovery and zero
forward recovery current with total capacitive charge of
17nC and total capacitance of 340pF. The die dimensions
of SiC diode (bare die) are 1.5mm × 1.5mm. With
commercialization and demand for further reduction,
even smaller bare-dies can be manufactured to cater to
this application.
JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.14, NO.6, DECEMBER, 2014
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699
5 mm
Filter Cap
1
AC IN
DC Out
L1
D1
D4
6
MOS1
MOS 1
5 mm
D3
D1
Gate
D5
D2
AC IN
Source
Source
D2
DC GND
2
4
5
MOS Trig
4
DC GND
Fig. 2. Package Circuit Details.
III. PACKAGE DIE AREA ESTIMATION
Die packaging plays an important role in connecting
die to the external circuit of the board, creating a path to
remove the heat generated by the devices during its
electrical operation, and protecting the die from the
external environment such as moisture, dust, etc [12].
Many of the reliability issues of power devices are either
related to excessive temperature or thermal fatigue due to
electrical cycling. Study has been currently done to
improve the cooling performance, reduce the thermal
resistance and reduce thermal expansion difference by
closely matching the coefficient of thermal expansion of
the package to that of the electrical die material which in
our case is SiC, increase the maximum operating
temperature of the packaging material by reducing the
thermal resistance and providing enough ways to cool the
package in shortest time [13]. Some of the most common
types of power semiconductor packages are TO-220, TO247, TO-262, TO-3, D2Pak, etc. The total package
substrate dimension of the converter circuit is 5 mm × 5
mm as shown in Fig. 3. Normal bond-wired packages
D3
D4
Fig. 3. Package substrate floor plan.
impose several limitations on power device applications
in electrical, thermal, volumetric and reliability
performance. In order to alleviate these issues, innovative
interconnect approaches of packaging technique which
has higher current carrying capability and handling high
thermal loads are required.
All the components together are housed in ceramic
package. This package offers a variety of benefits
including a small sized "near chip scale" footprint, thin
profile and low weight. It also uses perimeter I/O pads to
ease PCB trace routing, and the exposed copper die-pad
technology offers good thermal and electrical
performance. These features make the ceramic package
an ideal choice for many new applications where size,
weight, thermal and electrical performance are important.
Bottom side connections to die happen through bumps
and top side are bonded with thick metal strips as shown
in Fig. 4. Ceramic base is cut from top side to allow
housing of individual die components. Thin copper film,
on top of ceramic base, acts as die-to-die interconnect.
upper side thick
copper
Thicker Polymide
Copper Shim
Thin Film copper
Device
Epoxy
Lower side thick
copper
Fig. 4. Die package assembly details.
D5
Ceramic Base
700
RAJENDRA PRATAP et al : SIC BASED SINGLE CHIP PROGRAMMABLE AC TO DC
POWER CONVERTER
Ptotal = PMOS + 5 ´ Pdiode
Ptotal = 35 + 5 ´ 40 @ 235
(5)
(6)
The heat dissipation capacity of the package would
determine the current rating of the AC-to-DC converter
[16]. The temperature based operating parameter
variation of SiC diodes [17] is given by Eqs. (7)-(9)
Fig. 5. IDS vs VGS characteristic curve for SiC MOSFET.
V fwdT = VT + I fwd ´ RT
(7)
VT = 0.99 + ( T j ´ ( -1.5 ´ 10-3 ))
(8)
RT = 0.03 + (T j ´ ( 0.5 ´ 10-3 ))
(9)
Thicker copper film is used for die to outside package
connections. The large solder balls with 300 μm solder
width and 250 μm solder height can be used for bottom
side copper film to package and board connections.
These have high current carrying capability. The solder
pads are distributed over the package substrate surface.
So, the solder balls become the electrical, thermal and
mechanical connections for the power device.
Here TJ is diode junction temperature in Degree
Celsius
In conventional transformer based circuits, thermal
calculations for voltage regulator are done using virtual
junction temperature as given in Eq. (10)
IV. THERMAL ANALYSIS
where Tjn is operating virtual junction temperature and is
generally 1500C and θjA is rated at 230C/W.
If the transformer efficiency is assumed to be 87%
operating at 230 V AC input supply voltage and 1500C
temperature and similarly diode rated for 5A range
having power consumption of 0.1 W/0C range, then total
power for the transformer based power supply assembly
for 230V input AC, 5A load, 1500C operating virtual
junction temperature, would come in the range of
Thermal analysis has been performed for the proposed
converter and compared with the conventional converter
consisting of a transformer and Si based devices. Total
power is calculated for the proposed converter which will
get dissipated at 10A steady state forward current ratings
for MOSFET and diodes. The RON of the MOSFET used
in the circuit CPMF-1200-S080B is 80 mΩ and the
MOSFET has negative temperature coefficient as shown
in Fig. 5, which means as the temperature rises, faster
response and higher IDS current can be obtained at lower
gate voltage.
MOSFET is rated for steady state 30A forward current
at 1000C. The total power dissipation rated at 250C is
313W. For 10A load current, the power dissipation in the
MOSFET [14] would be ≈ 35W. The diodes used in the
circuit are rated for 26A forward current [15]. Total
Power dissipation per device is 377W at 250C and 163W
at 1100C at full load current. For a load current of 10A,
the power dissipation at 250C would be ≈40W per diode.
So the total power which is getting dissipated in the
form of I2R heat for 10A load current can be calculated
from Eqs. (5) and (6)
PD =
T jn(max) - TA
q jA
(10)
PD = PTransformer + 4 ´ Pdiode + Pregulator
(11)
150
= 216 W
23
(12)
PD = 150 + 4 ´ 0.1´ 150 +
Thus for worst case rated operating temperature of
1500C and 5A load, a conventional transformer based
AC-DC converter, power consumption (~216W) would
almost fall in the same range (~235W) as for SiC based
miniaturized converter. But SiC based converters can be
designed to operate for much higher power flow and
temperature ratings with much better reliability
parameters. The notable difference is that transformer
based converter would be operating at its peak stressed
operating conditions whereas SiC based converter would
JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.14, NO.6, DECEMBER, 2014
701
470 mF
FUSE 5 A
AC in
Filter
Cap
DC out
FUSE 5 A
L
O
A
D
230 V, AC
Mains
470 mF
0.01 mF
DC
GND
AC in
MOS
Trig
Pulse Width
Modulator (VCO)
+
-
Ramp Generator
Vref
Ramp
Comparator
Driver
Fig. 6. Typical Use Case Circuit.
be operating under least stress conditions. Thus operating
life of SiC based system would be longer as compared to
its silicon based counterpart.
V. ELECTRICAL ANALYSIS
Fig. 7. VDCOUT plotted against time.
IDiode (A)
For electrical analysis, the performance is obtained by
simulating the proposed converter as well as the
conventional converter. Fig. 6 shows the circuit where
proposed package is used to supply a load. Fuse breakers
connected at the input and the output pins are used as
protection elements to avoid any damage in case of any
failure in the circuit operation. The fuse rating can be
adjusted to the load requirements as against 5A shown in
the diagram. Four diodes used in the package are
CSD04060 and SiC MOSFET CMF20120D. By tuning
the MOSFET driver circuit pulse width, voltages as low
as 0.70 V can be obtained at the DC Out+ pin as shown
in Fig. 7, when an AC supply of 230V is used at the input
side. Simulation waveform in Fig. 7 shows power supply
net transients with pure resistive load and stable output
voltage of 5.4V which can be used as DC input for any
electronic digital circuit. The minimum stable DC
voltage which can be obtained using MOSFET gate
control is 0.07 V. Conventional DC power supply circuits
cannot generate stable supply below approximately 0.7V.
A typical usage may use the circuit at voltages viz., 5, 4.2,
3.6, 3.3, etc.
Fig. 8. Reverse recovery current through Si Diode.
Fig. 8 illustrates the reverse recovery current through
SiC based diode which is used in the proposed converter.
The reverse recovery current through Si diodes used in
conventional converter circuit is displayed in Fig. 9.
Large spikes appear in Si diodes which degrade the turnon time as well as power efficiency of the converter. Fig.
RAJENDRA PRATAP et al : SIC BASED SINGLE CHIP PROGRAMMABLE AC TO DC
POWER CONVERTER
IDiode (A)
702
Fig. 11. Converter Circuit used for spice and hardware
measurement.
IDrain (A)
Fig. 9. Reverse recovery current through SiC DIODE.
Fig. 10. MOSFET drain current during turn-on period.
10 illustrates the forward current through SiC based
MOSFET. It can be seen that the transient spikes are
almost zero which is again a merit of the proposed
converter.
For experimental measurement and validation of the
proposed single package ac-to-dc converter, complete
packaged part of SiC MOSFET CMF20120D and Diode
CSD04060 is taken from CREE Company and assembled
together to show the converter operation and
performance efficiency measurements done on the
experimental setup as shown in Fig. 11. In this circuit Vi
is a AC source and V2 is a high frequency pulse train
used to trigger MOSFET gate through a driver circuit.
Resistance R2 (10 Ω) in Fig. 11 is used to record the
current waveform through SiC MOSFET on DSO. The
experimental setup contains two test fixtures, one done
using Si diodes (MUR860) and Si MOSFET (IRF510)
and the other using SiC diodes (CDS04060) and SiC
MOSFET (CMF20120D). Fig. 12(a) shows the input AC
voltage Vi and rectified output voltage, Vr, with SiC
devices while output load voltage, VO, and regulated
voltage across capacitor VC along with gate pulses with
duty cycle of 66% are shown in Fig. 12(b).
Fig. 13 shows the ripple peak when Si devices were
used and Fig. 14 shows ripple peak with SiC devices
being used in the circuit. From the figures it is clear that
(a) Input voltage (upper trace: 200 V/div, 10 ms/div), Rectified
Output voltage (lower trace: 200 V/div, 10 ms/div)
(b) Voltage across C (upper trace: 50 V/div, 10 ms/div) and
Output voltage across R1 (lower blue trace: 10 V/div, 10 ms/div),
Gate pulses to MOSFET (red trace: 5 V/div, 10 ms/div) of AC to
DC Converter
Fig. 12. Experimental Results.
settling time and peak overshoot significantly are
reduced when SiC diode CSD04060 is used with respect
to Si diode MUR860. Reduction in peak overshoot
increases the converter efficiency.
Table 1 shows the settling time and peak overshoot
comparison of Si (MUR860) with SiC (CSD04060) diode
while Table 2 shows the improvement in ripple factor in
SiC diode in comparison to Si diode when used in buck
converter mode shown in Fig. 11. These data show how
SiC devices have better performance as compared to Si
devices [18]. SiC devices have negligible turn ON time
JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.14, NO.6, DECEMBER, 2014
703
VI. CONCLUSIONS
An attempt has been made to put forward a single chip
AC-to-DC converter using SiC diodes and SiC MOSFET
to achieve miniaturized single chip solution with higher
power efficiency. This reduces the number of discrete
components needed on the board thus reducing the bill of
material (BOM). The AC-DC modules already available
in the market are much bigger in size as compared to the
proposed 5 mm x 5 mm package die floor plan presented
in this paper. The advantages of the proposed circuit are
ability to connect high voltage AC supply directly to the
system board, single integrated circuit package having
very small footprint, much longer life cycle of the circuit
due to its operation under reduced stress conditions and
very high power efficiency of the converter circuit.
Volume production of SiC based devices would bring
down its overall manufacturing cost and would make it
comparable to available Si based discrete components.
Thermal analysis performed in the paper shows that these
devices would be very useful for use as miniaturized
power converters for load currents of up to 5-7A keeping
the package thermal conductivity limitation in mind.
Fig. 13. voltage waveform across Si diode.
Fig. 14. voltage waveform across SiC diode.
Table 1. Comparison of settling time and peak overshoot for Si
and SiC diodes
Turn-ON time
(Setting Time)
Peak Overshoot
Si Diode
06 m s
250 Mv
SiC Diode
01 m s
10 mV
REFERENCES
[1]
Table 2. Comparison of Ripple Factor for Si and SiC diodes
SiC Diode
V(rms)
V(Avg)
V(ref)
2.31
4.01
5.06
2.05
3.48
4.92
2.10
3.49
4.98
Si Diode
Ripple
Ripple
V(rms) V(Avg) V(ref)
Factor
Factor
0.519
0.572
0.519
2.33
4.05
5.69
2.00
3.48
4.83
[2]
2.10 0.578
3.48 0.618
4.98 0.627
and settling time as compared to Si devices. The large turn
ON ripples and large settling time of devices account for
most of the power losses incurred during device operation.
The board level assembly and simulations show promising
results for the proposed single packaged converter device.
The SiC MOSFET based AC-to-DC converter has a
settling time of 8s to 10s depending on the DC output
voltage expected to be achieved as shown in the transient
response curve in Fig. 7.
[3]
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Rajendra Pratap graduated from
University of Roorkee, India, in 1998,
in Electrical Engineering and
received the Master’s degree from
IIT Delhi, India, in Microelectronics
in 2005. He is Research student at
MNNIT Allahabad, working in the
field of Silicon Carbide MOSFETs.
Vineeta Agrawal graduated from
Allahabad, University, India, in 1980,
and received Master’s degree in
Electrical Engineering in 1984, from
the same University. She joined as
lecturer in 1982 in Electrical
Engineering Department in M. N. R.
Engineering College. During teaching, she did her Ph.D.
course in Power Electronics. At present she is Professor
in the Department of Electrical Engineering at Motilal
Nehru National Institute of Technology, Allahabad. Her
research interests are in single phase to three phase
conversion and AC drives. She has more than 100 papers
in Journals and conferences.
JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.14, NO.6, DECEMBER, 2014
Ravindra Kumar Singh is a
Professor of Electrical Engineering
at Motilal Nehru National Institute of
Technology Allahabad at Allahabad,
India. He is member IEEE, Fellow,
Institution of Engineers (India). His
areas of interest are DC- DC
converter, Electrical Drive & its applications. He has
published more than 70 papers in Journals and
conferences and supervised number of Doctoral thesis
work in different areas.
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