Application Note
USCi_AN0008 – July 2016
Utilizing Silicon Carbide in 80 Plus Current Average Power Factor Correction
John Bendel Abstract In an attempt to improve the efficiency and power factor of computing power supplies, the computer industry has created a voluntary certification program called “80 Plus”. In this application note, a silicon carbide cascode switch and boost diode will be evaluated in a 1 kW hard switch Power Factor Correction (PFC) board with respect to its suitability in 80 Plus applications. 1
80 Plus Table 1 gives the basic efficiency levels required for the various 80 Plus ratings. It is important to remember that these efficiencies are for the entire supply and not just for the PFC stage; therefore the PFC must significantly exceed the efficiencies in this chart. With respect to power factor, 0.90 or better is required for 20%, 50% and 100% of rated load with the exception of Platinum, which requires at least 0.95 power factor for servers. 80 Plus Test Type 115V internal non‐redundant 230V internal redundant 230V EU internal non‐redundant Percent of rated load 10% 20% 50% 100% 10% 20% 50% 100% 10% 20% 50% 100% 80 Plus 80% 80% 80% 82% 85% 82% 80 Plus Bronze 82% 85% 82% 81% 85% 81% 85% 88% 85% 80 Plus Silver 85% 88% 85% 85% 89% 85% 87% 90% 87% 80 Plus Gold 87% 90% 87% 88% 92% 88% 90% 92% 89% 80 Plus Platinum 90% 92% 89% 90% 94% 91% 92% 94% 90% 80 Plus Titanium 90% 92% 94% 90% 90% 94% 96% 91% 90% 94% 96% 94% Table 1 80 Plus efficiency level certification requirements 2
Power Factor Correction Topology This note will use a hard switch current average PFC, as shown in Figure 1. These designs are simple low cost solutions and suitable up to the 80 Plus, Gold level, and, depending on the switching frequency and power level, it is plausible to meet the Platinum level, or higher. The main drawback of this topology is that it will always carry the losses from the bridge. Ideal efficiency solutions reside in the more complex bridgeless topology. The Figure 1: Basic power factor correction topology “bridgeless” discussion is beyond the scope of this note, but if the highest efficiency is required; the reader is encouraged to look through USCi and other web material on bridgeless PFC implementations. USCi_AN0008 – July 2016 Utilizing Silicon Carbide in 80 Plus Current Average Power Factor Correction
United Silicon Carbide 1
Power facttor correction 3
www.unitedsiic.com
The
e Test Boarrd Figure 2 is a ppicture of the ttest board that produced the data presented in this note. Th
he Power Switch is a UJC0
06505K V, 45 mOhm m
maximum). Th
he advantage of the Cascode (650V
UJC06505K is not only its faast switching ccapability, but it can mance also be driven with standaard gate drivee. Its perform
mpete econom
mically against silicon capability allo ws SiC to com
ms are solutions. Ann RG_ON of 15 Ohms and RG__OFF of 51 Ohm
used to minim
mize EMI issuess, and all gate drive levels arre 0 to 14 V. An USCi Siliconn Carbide Diod
de, UJD06510TTS (650 V, 10 A
A) with a QC of 16 nC will be used ass the boost dio
ode. The inductor is ~ 350 µH at raated current. The Inductor iis implemented with Figure 2: U
UCC3818‐based PFC test board a a Magnetics Innc. 55438 coree, and 53 turn
ns of four‐straand 18 AWG wire. A complete list of compon
nents and alte
ernative comm
mercial inducto
ors can be foun
nd on USCi’s 9
90‐260 w
foun
nd in the application section. An interacctive Mathcad file based on
n Texas Instruments VAC PFC webpage, calculation
n is also availab
ble from the USSCi website. 4
Efficciency Currves The Figurre 3 efficiency ccurves versus in
nput voltage were run for lo
oads detailed in the 80 Plus specifications (10%, % and 100% off rated 20%, 50%
load) for a 1 kW PFC stage. Figure 3: Efficiency versus AC
C input voltage curve for a 91 kkHz hard switcheed PFC
These efficiency results will be u
used in the co
ontext of the 8
80 Plus certificates of Gold
d, Platinum and Titanium
m. The 80 Plus specificaation calls out two efficienccies at 230VA
AC, so in this ccomparison, when the efficciencies differ, the higher eefficiency will be used. 2 erage Power Faactor Correctio
on
Utilizing Silicon Caarbide in 80 Plus Current Ave
United Silicon Carbidee USCi__AN0008 – Julyy 2016
www.unite
edsic.com 5
Pow
wer factor corrrection
80 P
Plus Gold Figure 4 superimposes the efficien
ncy measurements from the previouss graph onto the 80 Pluss Gold specification. All powe
er factor meaasurements are greater thaan 0.95, and at the higherr power ratinggs are in the 0.99 range. Figure 4 Effficiency versus AC input voltage curves for 1 kW PFC dem
monstration bo
oard compared to the 80 Plus Gold requiremen
nts The efficiencies achievved well exce
eed the 80 Plus Gold speccification, bu
ut as mention
ned before, the 90 Plus spec is for the com
mplete powerr supply, not just the PFC sstage. The naarrowest deltta is 5.7% points at low line for f the 50% load l
line. Th
his equates to
o the final poower conversion stage neeeding to meeet or exceed 94
4% efficiency at this load line. As the secondary sta ge is operatin
ng from a reggulated outpu
ut and therefore allows for sttraightforwarrd optimizatio
on, this shoulld be well witthin a designer’s reach wiithout extraordin
nary efforts. 6
80 P
Plus Platinum Figure 5 superimpose
es the Platinum rating on the initial efficiency m
measurementts. As menttioned previouslyy, all power faactors are witthin the 80 Pllus specificatiion. Figure 5: Effficiency versus AC input voltaage curves for 1 1 kW PFC demoonstration board
d compared to the 80 Plus Plaatinum requiremen
nts The lowesst efficiency d
delta between the specificcation and booard is 3.7% p
points, once aagain at low line at the 50% load point. TThis correspon
nds to a finall power convversion stage requirementt of 96.1% to meet num rating. Obviously this is more diifficult than G
Gold, but ach
hievable. The average deelta is the Platin
5.7%, so it is even posssible to adjusst Rg, switchin
ng frequencyy, or inductor design to improve the traadeoff at this operating point if the system
m does not qu
uite meet the Platinum rating. 008 – July 2016
6 USCi_AN00
Utilizing Silicon Carb
bide in 80 Plus Current Averaage Power Facttor Correction
United Silicon Carbidee 3
Power facttor correction 7
www.unitedsiic.com
80 P
Plus Titanium The Titanium specificaation is the m
most difficult tto meet and typically reseerved for servvers. Figure 6 lays out the efficiencies e
in the same pattern as beffore, althouggh the additio
onal 10% loaad of Titanium
m has been added to the 20%
% load graph. Figure 6: Effficiency versus AC input voltaage curves for 1 1 kW PFC demoonstration board compared to the 80 Plus Tittanium requiremen
nts The narro
owest delta, o
once again att the low line
e 50% load pooint is 1.7% p
percentage points betweeen the PFC efficiency and the
e 80 Plus Tittanium specification. Thiis leaves thee final converrsion power stage efficiencyy requirementt to be 98.2%
%; not an imp
possible task,, and achievaable with thee latest Phasee Shift Bridge and LLC topologgies. 8
Sum
mmary It is hope
ed that this application a
note has show
wn that the hard switcheed current avverage PFC iss very viable in Gold rated 80 8 Plus supp
plies, and a plausible p
opt ion for the h
higher efficieency Platinum
m and e low Rds, an
nd switching speeds of USSCi’s 650V sillicon carbide cascodes an
nd JBS Titanium ratings. The
diodes givve designers component o
options when
n looking to m
meet the lateest efficiencyy and power ffactor requireme
ents in today’s high volum
me computer ssystems. 4 erage Power Faactor Correctio
on
Utilizing Silicon Caarbide in 80 Plus Current Ave
United Silicon Carbidee USCi__AN0008 – Julyy 2016