1. POWER FACTOR CORRECTION
Design considerations for optimizing performance & cost of continuous mode boost PFC circuits by
Supratim Basu,Tore.M.Undeland

2. High circulating currents
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

3. 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.

5. 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

6. Active high frequency power factor correction
Makes load behave like a resistor
Near unity load power factor
Load generating negligible harmonics

7. 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)

8. Block Diagram of an active PFC Circuit of CCM Boost converter

9. Mosfet & Diode switching waveforms showing switching losses

10. 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

11. RCD Snubber Circuits

12. Magnetic Snubber Circuit

13. Comparison of recovery time of various diodes

14. Comparision of RECOVERY TIME and COST of various diodes

15. Experimental Results

16. 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

17. Effect of Diode recovery current on Mosfet drain current with a SiC Diode

18. Effect of Diode recovery current on Mosfet drain current with a PFC specific diode

19. Effect of Diode recovery current on Mosfet drain current with a single package series connected diode

20. 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

21. Low frequency conducted emission
SiC Diode
Single package series connected diode
PFC Specific Diode

22. High frequency conducted emission
SiC Diode
Single package series connected diode
PFC Specific Diode

23. 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