CCM-BOOST Datasheet, PDF (6/18 Pages) Infineon Technologies AG – CCM PFC Boost Converter Design

CCM PFC Boost Converter Design
Design Note DN 2013-01
V1.0 January 2013
The power stage equations and transfer functions for CrCM are the same as CCM. The main differences
relate to the current ripple profile and switching frequency, which affects RMS and switching power losses
and filter design.
Figure 3.2 IRMS Normalized by I_A/I_B ratio in relation to current
waveshape
CCM operation requires a larger filter inductor compared to CrCM. While the main design concerns for a
CrCM inductor are low HF core loss, low HF winding loss, and stable value over the operating range (the
inductor is essentially part of the timing circuit), the CCM mode inductor takes a different approach. For the
CCM mode PFC, the full load inductor current ripple is typically designed to be 20-40% of the average input
current. This has several advantages:
(1) Peak current is lower, and the RMS current factor with a trapezoidal waveform is reduced compared
to a triangular waveform, reducing conduction losses (Fig 3.2).
(2) Turn off losses are lower due to switch off at much lower maximum current.
(3) The HF ripple current to be smoothed by the EMI filter is much lower in amplitude.
On the other side, CCM encounters turn on losses with the MOSFET, which can be exacerbated by the
boost rectifier commutation recovery loss due to Q_rr. For this reason, ultra-fast recovery diodes or silicon
carbide schottky diodes with no charge Q_rr are needed for CCM mode.
In conclusion, we can say that for low power applications, the CrCM boost has an advantage in losses and
power density. This advantage may extend to medium power ranges, however at some medium power level
the low filtering and the high peak current starts to become severe disadvantages. At this point the CCM
boost starts being a better choice for high power applications.
According to the above, and since this document is intended to support high power PFC applications, the
following are detailed design discussions and design examples for a CCM PFC boost converter.
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