POWER FACTOR CORRECTION
Design considerations for
optimizing performance &
cost of continuous mode
boost PFC circuits
by
Supratim Basu,Tore.M.Undeland
All rectified ac sine wave voltages with capacitive
filtering draw high amplitude discontinuous current
pulses rich in harmonics , causing:
Low input power factor
High circulating currents
There are many approaches to mitigate this
problem :
 Passive and Active power factor correction
 Passive and Active filtering of network
 Accepting non-sinusoidal voltage / current in the
system.
Passive Power Factor Correction
Simple inductive input filter
Inductor stores energy to maintain
conduction throughout half cycle
Hence reduces harmonic distortation and
improves power factor
But size, weight and cost limits it’s
application upto 200W
Active high frequency power factor correction
Makes load behave like a resistor
Near unity load power factor
Load generating negligible harmonics
Types of active PFC circuits with Boost
converter topologies
Hard switched
Soft switched using ZVT
Discontinuous Conduction mode (DCM)
Critical Conduction mode (CRM)
Continuous Conduction mode (CCM)
Block Diagram of an active PFC Circuit of
CCM Boost converter
Mosfet & Diode switching waveforms showing switching losses
Switching loss reduction strategies
RCD Snubber Circuits
Magnetic Snubber Circuits
Power Switch types - IGBT or MOSFET
Boost Diode Options
SiC Schottky Diodes
Single Package Series connected diodes
PFC specific single diodes
RCD Snubber Circuits
Magnetic Snubber Circuit
Comparison of recovery time of various diodes
Comparision of RECOVERY TIME and COST of various diodes
Rating
Typical
Recovery
time
Supplier
Cost in
USD
SDT12S60
12A, 600V
Zero
Infineon
7.69
DSEE 808CC
10A, 600V
30ns
IXYS
2.46
STTH806TTI
8A, 600V
30ns
ST Micro
1.82
PFC Specific
1SL9R1560P2
15A, 600V
25ns
Fairchild
1.42
PFC Specific
15ETX06
15A, 600V
18ns
IR
1.03
Diode Type
Part
Number
Sic Schottky
Single package
series
connected
Single package
series
connected
Experimental Results
PFC Specific Diode
Single Package
Series Connected
Diode
SiC Schottky
Diodes
Input AC Voltage
(RMS)
85 – 264V
85 – 264V
85 – 264V
Switching
Frequency
100kHz
100kHz
100kHz
Input Power (W)
652
1076
653
1078
642
1049
Output Power (W)
600
1006
598
998
597
1001
Efficiency
0.92
0.935
0.915
0.925
0.93
0.954
Effect of Diode Recovery Current on the
Switching Current at turn-on
The switch turn-on peak current was the lowest
for the SiC Schottky Diode and highest for the
Single Package Series Diode
Effect of Diode recovery current on Mosfet
drain current with a SiC Diode
Effect of Diode recovery current on Mosfet
drain current with a PFC specific diode
Effect of Diode recovery current on Mosfet
drain current with a single package series
connected diode
Conducted EMI generated by the PFC board
was measured separately for each of the
three diode types:
 Measurements were made at 90V AC input, 600W output load with
a 3mH common mode EMI filter connected at the input circuit

Low freq part of conducted emission spectrum ( 150kHz - 1
MHz) is almost unaffected by different diode types

High freq part of conducted emission spectrum ( 1 MHz 30MHz) is affected by diode behavior


SDT12S60 SiC Schottky diode generates lower noise
Increased EMI caused by STTH806TTI single package series
connected diodes is only about 4dBV
Low frequency conducted emission
Single package series connected diode
SiC Diode
PFC Specific Diode
High frequency conducted emission
SiC Diode
Single package series connected diode
PFC Specific Diode
OPTIMIZING PERFORMANCE BY DESIGN A SUMMARY
 Power levels < 200W - Critical conduction mode PFC may be considered
 Power levels > 200W - Hard switched CCM PFC is preferred
 Power levels < 1000W & sw. freq of 100kHz - PFC specific is the best choice
 Power levels > 1000W & sw. freq > 100kHz - Higher initial costs of SiC
Schottky diodes are justified
 Higher efficiency or higher sw. freq - ZVT resonant mode boost converter may
be considered
 Power levels < 600W - Older generation Mosfets like IRF460N(IR) could reduce
costs w/o affecting performance significantly