Cree Application Note: SiC Power Schottky Diodes

APPLICATION NOTE
SiC Power Schottky Diodes in Power-Factor
SiC Power Schottky Diodes in Power Factor
Correction CircuitsCorrection Circuits
by Ranbir
Richmond
BySingh
Ranbir and
SinghJames
and James
Richmond
Introduction
conditions; and complex EMI filtering
Electronic systems operating in the
systems. On the other hand, CCM circuits
600-1200 V range currently utilize silicon
offersilicon
low RMS
are stable
Electronic systems operating in the 600- to 1200-V range currently utilize
(Si) PiNcurrents,
diodes, which
tend to during
store
PiN diodes,
store large state. The
operation
underhas
light
load
condition,
and
large amounts(Si)
of minority
carrier which
charge tend
in theto
forward-biased
stored charge
to be
removed
by carrier
minority
the long storage
recombinationamounts
before theofdiode
can becarrier
turned charge
off. This in
causes
and turn-off
times. Power
devices
offer good
synchronization
with
SMPSmade
PWM
forward-biased
state.performance
The stored
chargeas compared
with silicon carbide
(SiC) show great
advantages
to those
with other
circuits,
butmade
require
an semiconductors.
ultrafast diode.
The prime benefits
theremoved
SiC Schottky
barrier recombination
diode (SBD) lie in its ability
to switch
fast fast
(<50recovery
ns), with diodes
almost zero
has toofbe
by carrier
Silicon
(Si) ultra
have
reverse-recovery
charge,
even
at
high
junction
temperature
operation.
The
comparable
silicon
PiN
diodes
(Si SBDs
before the diode can be turned off. This
highdrops)
Qrr (~
nC), which charge
increases
are not viable in the 600 V range because of their large on-state voltage
have100
a reverse-recovery
of
causes long storage and turn-off times.
significantly
di/dt,switching
forward elements
current and
100-500 nC and take at least 100 ns to turn-off. This places a tremendous
burdenwith
on other
in
madeforward
with Silicon
Carbide
temperature.
On the
contrary, the Qrr of SiC
the system inPower
terms ofdevices
the required
safe operating
area and the
switching losses
incurred.
(SiC) show great performance advantages
SBDs is relatively independent of these
compared
to those
made
other and telecom
In traditional as
off-line
AC-DC power
supplies
used with
in computer
applications,
the
ACbiggest
input sees
a large
parameters.
One of
the
applications
inductive (transformer)
load, which
power of
factor
lower than 1. A PFC circuit allows
semiconductors.
Thecauses
prime the
benefits
the to be substantially
for SiC
SBDs in the near future is in the
the AC input line
see near-unity
power
factor,
as required
requirements. The power-factor correction
SiCtoSchottky
Barrier
Diode
(SBD)
lie in itsby new legal
CCM
power
correction (PFC) circuit.
(PFC) circuits can be divided in two broad categories: Boost-converter driven in (1)factor
discontinuous-conduction
mode
ability to switch fast (<50 ns), with almost
(DCM) and (2) continuous-conduction mode (CCM). DCM circuits do not require high-speed rectifiers but suffer
zero
recovery charge,
even
at high
from: de-rating
of reverse
circuit components;
instability
under
light load conditions;
and complexDiodes
EMI filtering systems.
SiCoperation
Schottky
junction
temperature
operation.
Thestable during
On the other hand, CCM circuits offer low RMS currents, are
under light load condition, and
comparable Silicon
PiN PWM
diodes
(Si SBDs
offer good synchronization
with SMPS
circuits,
but are
require an ultrafast diode. Silicon (Si) ultrafast-recovery
Characteristics of SiC SBDS
diodes have high
Q
(~
100
nC),
which
increases
significantly
not viable
in the 600 V range because of with di/dt, forward current and temperature. On the
rr
600 V One
SiC of
SBDs
are presently
available
contrary, the Q
of SiC
SBDs
is relatively
independent
of these
the biggest
applications
for SiCin
their
large
on-state
voltage
drops) have
a parameters.
rr
SBDs in the near future is in the CCM power-factor correction (PFC) circuit.
the
1
A,
4
A,
6
A,
10
A
and
20
A
ratings
reverse recovery charge of 100-500 nC and
from
Cree
(www.cree.com).
Figure
1
shows
take at least 100 ns to turn-off. This places
a
typical
temperature
dependent
forward
a tremendous
burden on other switching
SiC Schottky
Diodes
characteristic of a 4 A / 600 V SiC SBD
elements in the system in terms of the
(CSD04060).
required forward safe operating area and
Characteristics of SiC SBDS
theare
switching
losses
incurred.
600-V SiC SBDs
presently
available
in the 1-A, 4-A, 6-A, 10-A
Introduction
applications, the AC input sees a large
inductive
(transformer)
load which due
causes
The on-resistance
increases
with temperature
to the
reduction in the
elevated
temperatures.
theelectron
power mobility
factor toat be
substantially
lower The
diode carries than
4 A at1.a VA
of 1.52 V at 25°C. The current reduces
F PFC circuit allows the AC input
to approximately
at thenear-unity
same VF atpower
200°C.factor,
This negative
line 2toA see
as
temperature coefficient of forward current allows us to parallel
required
by
new
legal
requirements.
The
more than one die in a package, or many in a circuit, without
Power Factor Correction
circuits
canhighany unequal current-sharing
issues. This (PFC)
behavior
is unlike
divided
in two
broad
Boost
voltage Si PiNbe
diodes.
Figure
2 shows
the categories:
reverse characteristics
of the 4-A / 600-V
SBD. The
typical leakage
is less than 20
converter
driven
in (1) current
Discontinuous
μA at 600 V atConduction
25°C which increases
50 μA at 200°C
a very
Mode to (DCM)
and —(2)
nominal increase
for
such
a
wide
temperature
range.
Continuous Conduction Mode (CCM). DCM
circuits do not require high-speed rectifiers,
but suffer from: de-rating of circuit
components; instability under light load
CPWR-AN01 Rev -
8
Forward Current (Amperes)
, Rev. A
e: CPWR-AN01
Application Not
and 20-A ratings from
Cree (www.cree.com).
Figure power
1 shows a
In traditional
off-line AC-DC
typical temperature dependent forward characteristic of a 4-A /
supplies used in computer and telecom
600-V SiC SBD (CSD04060).
o
25 C
o
50 C
6
o
100 C
o
75 C
o
125 C
o
150 C
4
o
175 C
o
200 C
2
0
0.0
SiC Schottky Diode
600 V, 4 Amp
CSD04060
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
Forward Voltage Drop (Volts)
Figure 1: The forward characteristics of a 4
Figure 1: The forward characteristics of a
A/600 V SiC SBD.
4-A/600-V SiC SBD.
Subject to change without notice.
www.cree.com/power
Page 1/9
200 C
o
100 C
40
20
o
25 C
0
0
100
200
300
400
500
600
700
Reverse Bias (Volts)
Figure 2: The reverse characteristics of a 4
A/600 V
Figure
2:SiC
TheSBD.
reverse characteristics of a
4-A / 600-V SiC SBD.
The devices were packaged in plastic TO220 packages. These parts are rated for a
The devices were packaged in plastic TO-220 packages.
maximum
junction
temperature
of temperature
175°C.
These parts
are rated
for a maximum
junction
For aForcase
temperature
of up
the the
of 175°C.
a case
temperature
of to
up150°C,
to 150°C,
junction
temperature
remains
below
175°C
at
full
junction temperature remains below 175°Crated
current.
at full rated current.
The turn-offThe
characteristics
of the 10-A / 600-V
turn-off characteristics
of theSiC
10SBD
are compared
with
a
Si
FRED
at
different
temperatures
A/600 V SiC SBD are compared with a Si
(Figure 3). The SiC diode,
being a majority carrier
device,
APPLICATION
NOTE
FRED at different
temperatures (Figure
3).
does not have any stored minority carriers.
The SiC diode, being a majority carrier
device, does not have any stored minority
10
carriers.
Therefore, there is no reverse
8
recovery current associated with the turn-off
transient
of the SBD. However, there is a
6
4
2
0
SiC 10 A/600 V SBD
TJ = 25, 50, 100, 150C
-2 600V, 10A Si FRED Rev CPWR-AN01
-4
TJ = 25C
TJ = 50C
TJ = 100C
TJ = 150C
Therefore, there is no reverse-recovery current associated
with
the amount
turn-off transient
of the SBD.current
However, there
small
of displacement
is a small amount of displacement current required to
required to charge the Schottky junction
charge the Schottky junction capacitance (< 2 A), which
(< the
2 A),
which is current
independent
iscapacitance
independent of
temperature,
level and di/dt.
of
the
temperature,
current
level
and exhibits
di/dt. a large
In contrast to the SiC SBD, the Si FRED
amount
of
the
reverse-recovery
charge,
which
In contrast to the SiC SBD, the Si FRED increases
dramatically
temperature,
and reverse di/
exhibits a with
large
amount on
of current
the reverse
dt.
For
example,
the
Qrr
of
the
Si
FRED
is
approximately
recovery
charge,
which
increases
160 nC at room temperature and increases to about 450
dramatically
withexcessive
temperature,
current
nC
at 150°C. This
amounton
of Q
increases the
rr
and
reverse
di/dt.
For
example,
the
rr of
switching losses and places a tremendousQburden
on the
the Siand
FRED
160 nC at
switch
diode is
in approximately
typical PFC applications.
room temperature and increases to about
450 nC at 150°C. This excessive amount of
PFC
Qrr Circuits
increases the switching losses and
places a tremendous burden on the switch
Aand
simple
CCM
circuit
is shown
in Figure 4. This circuit
diode
inPFC
typical
PFC
applications.
achieves near-unity power factor by chopping the full
wave-rectified input with a fast switch (MOSFET) and then
PFC Circuits
stabilizing
the resulting DC waveform using a capacitor.
When Athe
MOSFET
is ON,
is necessary
to prevent
the
simple
CCM
PFCit circuit
is shown
in
current
the achieves
output capacitor
or the load
Figure to4. flow
Thisfrom
circuit
near-unity
through the MOSFET. Hence, when the Diode is ON, the
power factor by chopping the full wave
FET is OFF, and vice versa.
rectified input with a fast switch (MOSFET),
and then stabilizing the resulting DC
waveform using a capacitor.
When the
L
Diode
MOSFET is ON, it is necessary to prevent
the current to flow from the output capacitor
or the load through the MOSFET. Hence,
when the Diode is ON, the FET is OFF, and
vice versa.
FET
Cout
DC Output
Leakage Current (µA)
o
60
Time (s)
Figure 3: Turn-off switching waveform of the
10 A / 600 V SiC SBD in comparison to Si
FRED (IXYS DSEI 12-06A).
Bridge Rectifier
SiC Schottky Diode
600 V, 4 Amp
CSD04060
80
-10
-1.0E-07 -5.0E-08 0.0E+00 5.0E-08 1.0E-07 1.5E-07 2.0E-07
AC Input
100
Current (A)
with
in the
atures.
2 V at
mately
egative
current
ie in a
ut any
This
i PiN
everse
D. The
µA at
µA at
such a
diodes.
Figure 2 shows the reverse
characteristics of the 4 A / 600 V SBD. The
typical leakage current is less than 20 µA at
600 V at 25°C which increases to 50 µA at
200°C – a very nominal increase for such a
wide temperature range.
Figure 4: A simple CCM PFC boost circuit for
Figure
4:applications.
A simple CCM PFC boost circuit
off-line
Page 2/9
for off-line applications.
During the switching transient when the
Diode
is turning
OFF when
and the
is
During the switching
transient
the MOSFET
Diode is turning
-8
OFF and
the
MOSFET
is
turning
ON,
the
reverse-recovery
turning ON, the reverse recovery current
currentfrom
from the
the diode
thethe
MOSFET,
in addition
Diodeflows
flowsinto
into
MOSFET,
in
-10
to
the
rectified
input
current.
This
results
in
a
large
inrush
-1.0E-07 -5.0E-08 0.0E+00 5.0E-08 1.0E-07 1.5E-07 2.0E-07
addition to the rectified input current. This
current into the MOSFET, necessitating its substantial deTime (s)
results
in a tolarge
inrush
current
into had
the no
rating as
compared
the case
where
the diode
Figure 3: Turn-off switching waveform of the
MOSFET,
necessitating
its
substantial
dereverse-recovery current. This large MOSFET represents a
10 A /3:600
V SiC switching
SBD in comparison
Figure
Turn-off
waveformto
of Si
rating
asincompared
the switching
case where
thealso
substantial
cost
this circuit.to
These
losses
FRED
(IXYS
DSEI SiC
12-06A).
the
10-A
/ 600-V
SBD in comparison
limit the
frequency
of reverse
operation,
and thecurrent.
efficiency
of the
Diode
had no
recovery
This
to Si FRED (IXYS DSEI 12-06A).
circuit, and
hence
its
cost,
size,
weight
and
volume.
A
higher
large MOSFET represents a substantial
small amount of displacement current
frequency would allow the size of the passive components
cost in this circuit. These switching losses
required to charge the Schottky junction
to be correspondingly smaller. Many fast silicon rectifiers
also limit the frequency of operation, and
capacitance (< 2 A), which is independent
the efficiency of the circuit, and hence its
of the temperature, current level and di/dt.
cost, size, weight and volume. A higher
In contrast to the SiC SBD, the Si FRED
frequency would allow the size of the
exhibits a large amount of the reverse
passive components to be correspondingly
Cree, Inc.
recovery
charge,
which
increases
4600 Silicon
Drive
smaller.
Many
fast
silicon
rectifiers
also
Copyrightdramatically
© 2002-2006 Cree, Inc.
All rights
reserved. The information
in this document is subject to change without notice. Cree
Durham, NC 27703
with
temperature,
on
current
and the Cree logo are registered trademarks of Cree, Inc.
USA Tel: +1.919.313.5300
show “snappy” reverse recovery,
which
and reverse di/dt. For example, the Qrr of
Fax: +1.919.313.5778
results
in
a
large
EMI
signature,
which
are
www.cree.com/power
CPWR-AN01,
A
the
Si FRED Rev.
is approximately
160 nC at
also
unacceptable
to
the
new
European
room temperature and increases to about
-6
req
reve
effic
with
nea
rect
sho
of c
ma
rect
curr
flow
Hig
and
(>2
req
circ
p-ireco
elim
circ
dehigh
snu
600
pow
sec
–2
Figure 4: A simple CCM PFC boost circuit for
off-line applications.
also show During
“snappy”
which
results
thereverse-recovery,
switching transient
when
the in a
large EMI signature, which is also unacceptable to the new
Diode is turning OFF and the MOSFET is
European requirements. A fast rectifier with near-zero
turning ON,
recovery PFC
current
reverse-recovery
willthe
allowreverse
for high-efficiency
circuits,
the Diode
flowslegal
intorequirements.
the MOSFET, in
which from
also comply
with new
addition to the rectified input current. This
A SiC results
diode isinsuch
a rectifier.
near-zero
a large
inrushThis
current
into reversethe
recovery
SiC
Schottky
rectifier
offers
low
switching
losses
MOSFET, necessitating its substantial dewhile still showing comparable on-state performance of
rating as compared to the case where the
conventional silicon rectifiers. Due to the majority carrier
Diode
had no of
reverse
This
transport
properties
these recovery
rectifiers, current.
they show
only a
largecurrent
MOSFET
a transient,
substantialwhich
capacitive
duringrepresents
their turn-off
flows through
MOSFET.
cost in the
thispower
circuit.
These switching losses
also limit the frequency of operation, and
the efficiency of the circuit, and hence its
High-Power
Circuits
cost, size,PFC
weight
and volume. A higher
frequency would allow the size of the
SiC SBDs
offer substantial
cost,
efficiency benefits
passive
components
tosize
be and
correspondingly
in higher
power
(>250
watts)
PFC
circuits.
Suchalso
circuits
smaller. Many fast silicon rectifiers
require the use of passive or active snubber circuits when
show “snappy” reverse recovery, which
operated even with ultrafast Si PiN rectifiers in order to
in a large EMI
signature,
which
are
negateresults
its reverse-recovery
charge.
SiC SBDs
are expected
also
unacceptable
to
the
new
European
to eliminate the requirement for these snubber-circuit
showing comparable on-state performance
of conventional silicon rectifiers. Due to the
majority carrier transport properties of these
rectifiers, they show only a capacitive
current during their turn-off transient, which
flows through the power MOSFET.
The schematic diagram of the PFC stage of this power
HighisPower
supply
shown in PFC
Figure Circuits
5. This PFC stage uses two 500V / 14-A, MOSFETs (IRFP450) in parallel (not shown) and
SiC SBDs offer substantial cost, size
a dual 600-V / 4-A MURH860CT as PFC diode, and snubber
and efficiency
benefits
in higher
power
diode.
The snubber
components
re-direct
the reverse(>250 Watts)
PFC the
circuits.
Such
circuits
recovery
charge from
PFC diode
to an
alternative bias
require the
use of passive
snubber
network.
A snubber
inductoror
(Lactive
) in series
with the PFC
S
diode
a snubber
capacitor
)
in
series
with
circuitand
when
operated
even(C
with
ultrafast
Sia snubber
S
diode
provide the
necessary
lag foritsthe
re-direction of
p-i-n rectifiers
in order
to negate
reverse
this reverse-recovery current away from the two power
recovery charge. SiC SBDs are expected to
MOSFETs during its turn-on transient. Switching waveforms
eliminate
requirement
for these i.e.
snubber
were
takenthe
under
full-load condition,
a 2 Ω load for
components,
as a severely
acircuit
28-V output
voltage.as
Thewell
operating
frequency was 95
de-rated
whilewere
stillconducted
offering under
a
kHz,
and allMOSFET,
measurements
room
temperature
ambient.
higher efficiency.
A 390
Watt power
with passive
Switching
waveforms
usingsupply
Si diodes
The
measured
currentand voltage-switching
snubber
circuits
was used
for evaluation ofwaveform
on
diodeSBDs
are shown
in Figure The
6 (a). These
600theV Si
/ 4PFC
A SiC
(CSD04060).
measurements
takencomposed
under full-load
and
power supplywerewas
of condition
two
an input voltage of 85 V AC. This condition represents the
sections: a PFC stage, which takes in 85 V
highest duty cycle for the diode, with the snubber. A peak
– 265 V as AC input
voltage
it towhen this
reverse-recovery
current
of 1.8and
A isboosts
observed
CS
Snubber Diode
PFC Diode
LS
FET
Cout
Snubber
Bias Network
SMPS 390-28 V
Bridge Rectifier
AC Input
85 V – 265 V
LBoost
DC Output
390 V
Brid
FET
Figure 5: High Power PFC circuit with snubber components.
Figure 4: High Power PFC circuit with snubber components.
CPWR-AN01 Rev components, as well as a severely de-rated MOSFET, while
still offering a higher efficiency.
A 390-watt power supply with passive snubber circuits was
used for evaluation of 600-V / 4-A SiC SBDs (CSD04060).
The power supply was composed of two sections: a PFC
stage, which takes in 85 V – 265 V as AC input voltage
and boosts it to 390 V DC output; a step-down SMPS,
which steps down the DC voltage from 390-V to 28V
output.
Copyright © 2002-2006 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree
and the Cree logo are registered trademarks of Cree, Inc.
CPWR-AN01, Rev. A
Page 3/9
diode turned off at a reverse di/dt of 200 A/µsec. A turn-on
dv/dt of 3.5 kV/µsec was used when the diode transitions
from OFF-state to ON-state. The switching waveforms on
the Si snubber diode used in conjunction with the main PFC
diode are shown in Figure 6 (b). It can be seen that this
snubber diode does not contribute any reverse-recovery
current that needs to flow through the MOSFET because it
is not carrying any forward current during the PFC diodeswitching transient. This diode provides a small voltage
transient to the PFC diode, which prevents it from turning
off too fast.
Cree, Inc.
4600 Silicon Drive
Durham, NC 27703
USA Tel: +1.919.313.5300
Fax: +1.919.313.5778
www.cree.com/power
APPLICATION
APPLICATION NOTE
NOTE
-300
-300
-9
-9
-400
-400
-12
-12
-500
-750n
-500
-750n
-700n
-700n
-650n
-600n
-650n
-600n
Time (s)
-550n
-550n
0
0
10
10
-100
-100
5
5
-200
-200
0
0
-300
-300
-5
-5
-400
-400
-10
-10
-500
-500-5µ
-5µ
Excess Reverse Recovery Current
0
0
0
0
-100
-100
-8µ
-8µ
Figure 7: MOSFET Current and Voltage turn-
In order toInascertain
the
of the the
snubber
network
order
to effect
ascertain
effect
of on
snubber
network
on
the
MOSFET
and
PFC
the MOSFET
and
PFC
diode
switching,
the
snubber
network
snubber
network on
thesnubber
MOSFET
and PFC
diode from
switching,
network
was
was removed
the PFCthe
circuit.
The measured
MOSFET
diode
switching,
the
snubber
network
was
from the
PFC
circuit.
The 8.
current removed
without a snubber
network
is shown
in Figure
removed
the reverse
PFC
circuit.
The a
The peak
current from
dueMOSFET
to diode
recovery
increases
measured
current
without
measured
MOSFET
current
without
a the
from 1.8
A with the
snubber
6.5
A without
snubber
network
is network
shown
into Figure
8. The
snubber
network.
This is
obviously
stresses
the
MOSFET
snubber
network
shown
in
Figure
8.
The
peak current due to diode reverse recovery
excessively
and maydue
lead todiode
an excessive
thermal load to
peak
current
reverse
increases
from to1.8
A with
therecovery
Snubber
the entire
circuit
assembly.
increases from 1.8 A with the Snubber
network to 6.5 A without the
network to 6.5 A without the
-15
0 -15
0
400
400
condition at an 85 V AC input is shown in
condition at an 85 V AC input is shown in
Figure 7. This circuit uses a Si PFC diode in
Figure
This
uses circuit.
a Si PFC
in
addition7. to
thecircuit
snubber
A diode
turn-on
addition to the snubber circuit. A turn-on
di/dt of 81 A/ µsec was measured and the
di/dt of 81 A/ µsec was measured and the
MOSFET turns on with a total current of
MOSFET turns on with a total current of
5.96 A, which decays to 3.44 A within a
5.96 A, which decays to 3.44 A within a
microsecond. This represents an excess
microsecond. This represents an excess
current of 2.52 A during turn on of the
current of 2.52 A during turn on of the
MOSFET.
MOSFET.
Page 4/9
Page 4/9
MOSFET Voltage (V)
200
200
6
6
100
100
3
3
0
0
0
-100
10.2µ
-100
10.2µ
MOSFET Current (A)
voltage transient to the PFC diode, which
Measurements
were also to
performed
on diode,
both MOSFETs
voltage transient
the PFC
which (in
prevents
it from
turning
off too
fast.
parallel)
in the PFC
circuit.
It was
found
that the current
prevents
it from
turning
off too
fast.
sharing was
fairly uniform between
theperformed
two MOSFETs.
Measurements
were also
on The
Measurements
were also performed
MOSFET voltageand current-switching
waveformson
under
both
MOSFETs
(inV AC
parallel)
in theinPFC
full-load
condition
at an 85(in
input is shown
Figure 7.
both
MOSFETs
parallel)
in the PFC
circuit.
It was
thatinthe
current
This circuit
uses
a Si found
PFC diode
addition
to sharing
the snubber
circuit.
It was
found
that the
current
sharing
fairly di/dt
uniform
between
the two and
circuit.was
A turn-on
of 81 A/µsec
was measured
was turns
fairly uniform
between of the
two
the MOSFET
with a
total current
5.96 and
A, which
MOSFETs. onThe
MOSFET
voltage
Thea microsecond.
MOSFET voltage
and
decaysMOSFETs.
to 3.44switching
A within
This represents
current
waveforms under
full load an
waveforms
under
full
load
excesscurrent
currentswitching
of 2.52 A during
turn-on
of the
MOSFET.
-2
-3
-4
12
0
10.3µ
10.4µ
10.3µ
10.4µ
Time (s)
MOSFET Current (A)
voltage switching waveforms.
-1
-5
MOSFET Switching 12
Si Diode;
No Snubber
MOSFET
Switching
9
Full Load;
85 V Input
Si Diode;
No Snubber
9
Full Load; 85 V Input
300
300
Figure 6(b):
6 (b) Snubber
Snubber diode
diodecurrentcurrent and
Figure
Figure
6 (b) Snubber
diode current and
and
voltage switching
waveforms.
voltage-switching
waveforms.
-3
10.5µ
-3
10.5µ
Time (s)
Figure 8: MOSFET Switching waveform
Figure
8:Snubber
MOSFET
Switching waveform
waveform
without
network.
Figure
8:
MOSFET
switching
without
Snubber
network.
without snubber network.
snubber network. This obviously stresses
snubber
network.
This obviously
stresses
thewaveforms
MOSFET
excessively,
and may
lead to
Switching
using
SiC Diodes
the
MOSFET
excessively,
and
may
leadentire
to
an
excessive
thermal
load
to
the
After these measurements were completed using Si diodes,
an
excessive
thermal
load
to
the
entire
the PFCcircuit
diode assembly.
was replaced with a SiC SBD (CSD04060),
circuit
assembly.
and all
components
of the snubber network, including
snubber inductor, capacitor and the bias network, were
removed and measurements were repeated. The measured
current- and voltage-switching waveforms on the Si PFC
CPWR-AN01 Rev CPWR-AN01 Rev -
Copyright © 2002-2006 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree
and the Cree logo are registered trademarks of Cree, Inc.
CPWR-AN01, Rev. A
-3
-6µ
-3
-6µ
-7µ
Time-7µ
(s)
Figure
7:
current and
turnFigure
7: MOSFET
MOSFET
andvoltage
Voltage
on waveforms
forCurrent
the case
with
Si turndiodes
on
waveforms
for
the
case
with
Si
diodes
onand
waveforms
for the case with Si diodes
Snubber
network.
and
network.
and snubber
Snubber network.
Time (s)
3
In order to ascertain the effect of
Snubber
Snubber
Diode
Diode
Current
Current
(A)(A)
Snubber
Snubber
Diode
Diode
Voltage
Voltage
(V)(V)
characteristics w/snubber.
15
15
3
Excess Reverse Recovery Current
Time (s)
Figure 6(a):
6: (a) SiSi PFC
PFC Diode turn-off
turn-off
Figure
Figure
6: (a)w/snubber.
Si PFC diode
Diode turn-off
characteristics
characteristics
w/snubber.
100
100
6
6
100
100
-15
-500n
-15
-500n
Time (s)
Snubber Diode Switching
Snubber
Full Load;Diode
85 V Switching
Input
Full Load; 85 V Input
-4µ
-3µ
-2µ
-1µ
-4µ
-3µTime (s)-2µ
-1µ
200
200
com
comp
wa
was
and
and
inca
includ
the
the
me
meas
me
meas
wa
wave
Fig
Figur
rev
rever
of
oftran
2.
trans
PFC Diode Voltage (V)
PFC
PFC
Diode
Diode
Voltage
Voltage
(V)(V)
-6
-6
9
9
MOSFET Current (A)
PFC Diode Switching
PFC
Diode85
Switching
Full Load;
V Input
Full
Load;
I PRR =
1.8 A85 V Input
I PRR = 1.8 A
-200
-200
-3
-3
PFC
PFC
Diode
Diode
Current
Current
(A)(A)
-100
-100
12
MOSFET Switching
Si Diode
+ Snubber
MOSFET
Switching
Full Load;
85 V Input
Si Diode
+ Snubber
Full Load; 85 V Input
300
300
0
0
Sw
Switc
12
MOSFET Current (A)
0
0
PFC
PFC
wn in
wn
00 Vin/
00 V /
el (not
el (not
4 A
4 A
ubber
ubber
-direct
-direct
e PFC
e PFC
ork. A
ork.
A
e PFC
e PFC
series
series
essary
essary
everse
everse
power
power
nsient.
nsient.
er full
er full
28 V
28 V
uency
uency
were
were
rature
rature
oltage
oltage
diode
diode
These
These
l load
l load
V AC.
V AC.
t duty
t duty
er. A
er. A
8 A is
8 A is
f at a
f at a
dv/dt
dv/dt
diode
diode
e. The
e. The
ubber
ubber
main
main
It can
It can
es not
es not
nt that
nt that
SFET
SFET
orward
orward
tching
tching
3
3
MOSFET Voltage (V)
MOSFET Voltage (V)
100
100
MOSFET Voltage (V)
which
which
to 28
to 28
400
400
Cree, Inc.
4600 Silicon Drive
Durham, NC 27703
USA Tel: +1.919.313.5300
Fax: +1.919.313.5778
www.cree.com/power
Fig
Figur
wav
wave
inp
input
swi
switc
con
cond
Fig
Figur
with
with
A tu
A and
tur
and
cur
curre
Sw
Switc
SIN
SING
recS
recov
size
size
the
there
diodes to ON-state.
100
SiC PFC Diode Switching
No Snubber
-200
-3
-300
-6
-400
0
-100
Diode Voltage (V)
0
-9
-500
10.3µ
10.4µ
10.5µ
-12
10.6µ
Time (s)
400
MOSFET Voltage (V)
-100
-100n
SiC Diode
Full Load;
85 V Input
0
50n
0
-300
-2
-400
-4
Time (s)
MOSFET
MOSFET removed
removed from
from previous
previous circuit)
circuit)
under
full
load
and
input
This diode
off at a reverse
of
under
full turned
load condition
condition
and an
andi/dt
input
voltage
of85
85A
AC.
voltage
of
VVAC.
510 A/µsec.
turn-on
dv/dt of 1.9 kV/ µsec
APPLICATION NOTE
was usedcurrentwhen and
the voltage-switching
diode transitions waveforms
from
The measured
OFF-state
to
ON-state.
The
MOSFET
on the Si PFC diode are shown in Figure 10 (a). This diode
turned
off
at a reverse
di/dt ofswitching
510
A/µsec.
A turn-on dv/dt
and current
waveforms
The voltage
measured
current
and
voltage
of
1.9
kV/µsec
was
used
when
the
diode
transitions
underwaveform
full load condition
85 Vdiode
AC input from
switching
on -the at
Sian
PFC
CPWR-AN01
Rev
OFF-state to ON-state. The MOSFET voltage- and currentis shown
in Figure
10 (b).
are shown
in Figure
10 (a).
switching waveforms under full-load condition at an 85-V
-3
9
-6
APPLICATION NOTE
The measured current and voltage
Figure
10(a):
diode
switching
Figure
10:
(a) SiC
SiC PFC
PFC
diode
switching
switching
waveform
on
the
Si PFC
diode
waveforms
with aa single
single MOSFET
(one
waveforms
with
MOSFET
(one
are shown in Figure 10 (a).
12
A turn-on di/dt of 362 A/µsec was measured
and the MOSFET
turns on at near-nominal
0
0
400
12
current level.
MOSFET Switching
2
-600
-8
10.20µ 10.25µ 10.30µ 10.35µ 10.40µ 10.45µ 10.50µ
Figure 9(a):
9: (a)SiCSiCPFC
PFCdiode
diodeturn-off
turn-off
Figure
waveforms under
under full
waveforms
full load
load condition
conditionand
andan
input
voltage
of
85
V
AC.
an input voltage of 85 V AC.
Switching waveforms using SiC Diodes100n
with
AC
input
are shown
(b).
This
diode
turned inoffFigure
at a 10
reverse
di/dt of
Time (s)
SINGLE
FET
200
6
510 A/µsec. A turn-on dv/dt of 1.9 kV/ µsec
Since 9SiC
no and
reverse
Figure
(b) diodes
MOSFEToffer
current
voltage was used400when the diode transitions from
12
100
3 condition
turn-on
under full
load
recovery,
it waveforms
may be possible
to reduce
the
OFF-state to ON-state. The MOSFET
SiCMOSFETs
PFC diode.used in the circuit,
300
9
sizeusing
of the
voltage and
current switching waveforms
0
thereby
saving cost, weight and size 0of the
under full load MOSFET
condition
at an 85 V AC input
Switching
circuit even further. This is because
200
6
1 FET, 10
SiC Diode
is
shown
in
Figure
(b).
-100
-3 severely
MOSFETs
used
in
PFC
circuits
are
Full Load; 85 V Input
-100n
-50n
0
50n
100n
de-rated due to
the additional switching
100
3
Time (s)
losses created by the reverse recovery
Figure
9 (b) that
MOSFET
current them
and voltage
voltage turn400
12
0
0
current
flow through
during
Figure
9(b):
MOSFET
current
and
Page 5/9
turn-on
waveforms
under
full load
loadcondition
condition
on waveforms
transients. under
As mentioned
earlier,
in this
turn-on
full
usingcircuit,
SiC PFC
PFC
diode.
300
9
-100
-3
using
SiC
diode.
two
MOSFETs were used in parallel
10.1µ
10.2µ
10.3µ
10.4µ
10.5µ
in order to achieve this de-rating. After the
Time (s)
MOSFET Switching
circuit
even using
further.
This with
is above
becauseFET
Switching
waveforms
SiC Diodes
SINGLE
200
6
1 FET, SiC Diode
measurements
presented
were
Since MOSFETs
SiC diodes used
offer in
noPFC
reverse
recovery,
it may be
circuits
are
severely
Full Load; 85 V Input
a MOSFET
was removed,
Figure 10(b): Single MOSFET current- and
possible
tocompleted,
reduce
the MOSFETs
used in and
the
(b)
Single MOSFET current and
voltage
de-rated
duethetosize
theof operated
additional
switching
100
3
voltage-switching
waveforms under
full
the
circuit
was
with
the
SiC
circuit, thereby saving cost, weight and size of the circuit
switching waveforms under full load
losses
created
by
the
reverse
recovery
load condition using SiC PFC diode.
Schottky
diode without
anyused
snubber
even further.
This is because
MOSFETs
in PFCcircuit.
circuits
condition
using SiC PFC diode. 0
0
currentde-rated
that flow
them during
turn-losses
are severely
duethrough
to the additional
switching
on transients. As mentioned earlier, in this
-100
-3
circuit, two MOSFETs were used in parallel
10.1µ
10.2µ
10.3µ
10.4µ
10.5µ
100
6
in order to achieve this de-rating. After the
Time (s)
Diode
Switching were
measurements
presented
above
Efficiency
and
Temperature
0
4
SiC Diode; 1 FET
Cree, Inc.
completed, a MOSFET was Full
removed,
and
Load; 85 V Input
4600 Silicon Drive
Measurements
(b)
Single
MOSFET
current
and
voltage
Copyright © 2002-2006-100
Inc. All rights reserved. The information in this document
is subject to change without notice. Cree
Durham, NC 27703
the circuitCree,was
operated with the SiC2
and the Cree logo are registered trademarks of Cree, Inc.
Tel:
+1.919.313.5300
switchingIn waveforms
under
fullUSA
load
the
test
circuit,
it
was
difficult
to
Fax: +1.919.313.5778
Schottky diode
without any snubber circuit. 0
-200
condition
using
SiC
PFC
diode.
www.cree.com/power
CPWR-AN01, Rev. A
separate the efficiency of the PFC circuit
-300
-2
and the next stage, which was the voltage
MOSFET Voltage (V)
-50n
MOSFET Voltage (V)
MOSFET Voltage (V)
MOSFET Current (A)
MOSFET Current (A)
Diode Current
e Voltage (V)
(b) S
switc
cond
Effic
Mea
4
-200
-500
MOSFET Switching
The MOSFET voltageand current-switching
waveforms
The MOSFET
voltage
and current
SiC Diode
300 waveforms
9
under full-load
condition
at an 85-V
AC
input
is shown
in
Full
Load;
85full
V Input
switching
under
load
Figure condition
9 (b). Thisatmeasurement
was
taken
with
SiC
PFC
an 85 V AC input is shown in
diode and no snubber
circuit. A turn-on di/dt of 362 A/µsec
200
6
Figure
9
(b).
This
measurement
taken
was measured, and the
MOSFET
turns on atwas
near-nominal
SiC PFC diode, and no snubber circuit.
currentwith
level.
100
3
6
Diode Switching
SiC Diode; 1 FET
Full Load; 85 V Input
Diode Current (A)
PFC Diode Voltage (V)
-100
300
-
3
MOSFET Current (A)
resses
ead to
entire
0
MOSFET Current (A)
veform
circuit was operated with the SiC Schottky diode without
any snubber circuit.
PFC Diode Current (A)
ect of
d PFC
rk was
. The
out a
8. The
covery
nubber
de-rated due to the additional switching
losses created by the reverse recovery
current that flow through them during turnon transients. As mentioned earlier, in this
circuit, two MOSFETs were used in parallel
in by
order
achieve this de-rating.
After
created
the to
reverse-recovery
current that
flow the
through
measurements
presented
above
them during turn-on transients. As mentioned were
earlier, in
completed,
a MOSFET
was inremoved,
this circuit,
two MOSFETs
were used
parallel inand
order to
achieve
this
de-rating.
After
the
measurements
the circuit was operated with the presented
SiC
aboveSchottky
were completed,
a MOSFET
was removed,
diode without
any snubber
circuit.and the
MOSFET V
T Current (A)
including snubber inductor, capacitor and
the bias network; were removed, and
measurements
were
repeated.
The
0
measured current and voltage switching
waveform on the Si PFC diode are shown in
-3
Figure 9 (a). This diode turned off at a
µ
reverse
of 5679 A/µsec.
turn-on
dv/dt
diode are
showndi/dt
in Figure
(a). ThisAdiode
turned
off at
a reverse
di/dtkV/µsec
of 567 A/µsec.
A turn-on
2.7 kV/
of 2.7
was used
whendv/dt
the of
diode
used when
theOFF-state
diode transitions
from OFF-state
transitions
from
to ON-state.
e turn- µsec was
3
I
sepa
and t
stephere
as w
stage
impa
efficie
these
comp
the e
diode
The l
to 10
Si diode, the entire snubber network was
included in the measurement, while in the
case of SiC diode, it was removed. The
case where only a single MOSFET was
used is also plotted in this figure. As in most
PFC circuits, the efficiency of the circuit
increases
as the load is Measurements
increased from 10
Efficiency and
Temperature
% to 100 %.
the case of single FET. At 100% load
condition, the total efficiency improves from
78.9 % for the Si diode case to 81.77 % for
the case of SiC diode with 2 FET; which
decreases to 80.7 % for the case with a
single FET. The slightly higher on-state
losses in SiC Schottky diode results in the
relatively smaller gain in the overall circuit
efficiency under full load operating
In the test circuit, itThe
was measurements
difficult to separate
at 85theVefficiency
input of the PFC circuit and the next stage, which was the voltage
condition. of
In the
general,
the efficiency
of the
step-down. Thevoltage
efficiency
numbers reported
include the efficiency
PFC stage
as well as
the SMPS voltage
are presented,
which here
represents
maintains
a more
uniform
profileiswith
step-down stage of the power supply. Hence, the impact of SiCcircuit
on the
PFC stage
circuit
efficiency
somewhat underthe highest stress for the active components
estimated in these measurements. Figure 11 shows the comparison
of thediode
measured
efficiencytoof the
the entire power
a SiC PFC
as compared
At 10 % load, the circuit
supply betweeninSithe
andcircuit.
SiC diode.
traditional design using Si diodes.
efficiency increases from 51.4 % for the Si
diode between
case to 57.5
% for SiC
The load was varied
10 percent
(20diode
Ω) towith
100 2percent (2 Ω) for its 28-V output, in 10 percent increments. As
mentioned earlier, in the case of the Si diode, the entire snubber network was included in the measurement, while in the
case of the SiC diode, it was removed. The case where only a single MOSFET was used is also plotted in this figure. As
in most PFC circuits, the efficiency of the circuit increases as the load is increased from 10 percent to 100 percent.
90
Power Efficiency (%)
80
SiC
70
60
Si
50
85 V Si Diode with Snubber
85 V SiC Diode with 2 FETs
85 V SiC Diode with 1 FET
40
30
0
20
40
60
80
100
Load (%)
Figure 11: Efficiency comparison of PFC circuit with Si and SiC diodes.
The efficiency of the circuit with single FET remains better than that
with two
FETs.
Figure
11: Efficiency
comparison of PFC circuit with Si and SiC diodes. The
efficiency of the circuit with single FET remains better than that with two
FETs.
The measurements at
85-V input voltage are presented, which represents the highest stress for the active components
in the circuit. At 10-percent load, the circuit efficiency increases from 51.4 percent for the Si diode case to 57.5 percent
for SiC diode with two FETs and increases further to 58.5 percent for the case of a single FET. At 100-percent load
condition, the total efficiency improves from 78.9 percent for the Si diode case to 81.77 percent for the case of SiC
diode with two FETs, which decreases to 80.7 percent for the case with a single FET. The slightly higher on-state losses
in a SiC Schottky diode results in the relatively smaller gain in the overall circuit efficiency under full-load operating
condition. In general,
the efficiency
diode
CPWR-AN01
Rev - of the circuit maintains a more uniform profile with a SiC PFC
Page
7/9as compared to
the traditional design using Si diodes.
Figure 12 shows the measured MOSFET case temperature as a function of time after initial power up. Initially, the devices
were in thermal equilibrium at room temperature. This measurement was done when full-load operating condition was
Copyright © 2002-2006 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree
and the Cree logo are registered trademarks of Cree, Inc.
CPWR-AN01, Rev. A
Cree, Inc.
4600 Silicon Drive
Durham, NC 27703
USA Tel: +1.919.313.5300
Fax: +1.919.313.5778
www.cree.com/power
impressed
on
this
circuit.
These
the case with Si diode, For the 85 V input
measurements were taken under two
voltage, the MOSFET case temperature
extreme input voltages – 85 V and 250 V.
decreases from a steady state temperature
Since a higher duty cycle is used in the
of 45.5 oC to 42.5 oC when the SiC PFC
case of 85 V input voltage, the MOSFET
diode is introduced for the case of 2 FETs.
sees
a
higher
reverse
recovery
current
Whentwo one
FET
removed,
its V. Since a
impressed on this circuit. These measurements were taken under
extreme
input was
voltages
–o 85 V and 250
causing
it
to
have
a
higher
case
temperature
stabilizes
at
47.6
C,
a
small
higher duty cycle is used in the case of 85-V input voltage, the MOSFET sees a higher reverse-recovery current, causing
it to temperature.
have a higher case
250-V input
the MOSFET
case temperature
decreases
from a steadyFor temperature.
250 V inputFor
voltage,
the voltage,
increase
as compared
to the original
case
stateMOSFET
temperature
of 35.7°C
when adecreases
Si PFC diode
is used to 30.2°C
for the case with
case
temperature
from
with when a SiC PFCSidiode is introduceddiode.
two FETs. When a FET was removed, the case temperature on the single FET was only 32.5°C, which is an improvement
over the case with Si diode. For the 85-V input voltage, the MOSFET case temperature decreases from a steady-state
temperature of 45.5°C to 42.5°C when the SiC PFC diode is introduced for the case of two FETs. When one FET was
removed, its temperature stabilizes at 47.6°C, a small increase as compared to the original case with a Si diode.
50
o
MOSFET Case Temperature ( C)
55
Si Diode 2 FETs Snubber
SiC Diode 2 FETs
SiC Diode 1 FET
85 V Input
45
40
35
30
250 V Input
25
10
100
1000
Time (secs)
Figure 12: MOSFET case temperature comparison for the following cases at 85-V
and 250-V input: Si diode with two FETs, SiC diode with two FETs and SiC diode
with single FET.
Figure 12: MOSFET case temperature comparison for the following cases at 85 V and
250 V input: Si diode with 2 FETs, SiC diode with 2 FETs and SiC diode with single
Conclusions
FET.
The realization of the impact of SiC SBDs on the circuit efficiency and MOSFET case temperature is of great importance
to a PFC circuit designer. Based on measurements presented above, the most significant advantages offered by SiC
Schottky diodes vis-à-vis Si PiN diodes in a PFC circuit are: higher circuit efficiency; lower FET case temperature; and a
significant reduction in the number of circuit components due to the elimination of the snubber inductors, capacitors and
networks. These advantages can be very effectively harnessed for lowering the cost of the circuit. For a given efficiency,
a higher
frequency ofRev
operation
of the circuit can result in smaller (and hence cheaper) inductorsPage
and MOSFETs,
which
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are typically the most expensive components in the PFC circuit. For an identical case temperature, a smaller and cheaper
MOSFET and heat sinks can be used in the circuit. Another simple circuit modification to lower the total circuit losses
involves reducing the gate resistance of the MOSFET. A higher gate resistor is used in typical PFC circuits in order to
limit the di/dt in the Si PiN diode, which might result in excessive reverse-recovery current and EMI emissions. Since SiC
Schottky diodes can operate under very high di/dt, a smaller MOSFET gate resistance can be utilized, further reducing
MOSFET turn-on losses. Such a modification will also result in lowering the MOSFET turn-OFF losses, which showed little
change with direct replacement of SiC Schottky diodes with Si PiN diodes in the PFC circuit described above.
The resulting circuit is much more simplified and reduces manufacturing costs, design errors, and the number of
components that emit and absorb harmful EMI. Overall, this can also result in improved circuit reliability.
Copyright © 2002-2006 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree
and the Cree logo are registered trademarks of Cree, Inc.
CPWR-AN01, Rev. A
Cree, Inc.
4600 Silicon Drive
Durham, NC 27703
USA Tel: +1.919.313.5300
Fax: +1.919.313.5778
www.cree.com/power