What is an interleaved PFC?
An interleaved PFC is a boost power-factor-correction stage split into two (or more) parallel legs whose switches are driven 180° out of phase (for N phases, 360°/N apart). It keeps all the benefits of the ordinary boost PFC — unity power factor, regulated DC bus — while adding ripple cancellation and current sharing.
Ripple cancellation — topic-specific
Because the two legs switch half a period apart, the peaks of one leg's triangular ripple line up with the valleys of the other. When the currents add at the input, much of the ripple cancels: for two phases the input-current ripple can fall to a quarter of a single leg's, and it goes to zero at 50% duty. The effective ripple frequency doubles, so the EMI filter is smaller and lighter.
Current sharing and phase shedding
Each leg carries half the total current, so the inductors, switches and diodes run cooler and can be smaller. At light load the controller can turn one leg off — phase shedding — to keep efficiency high. This makes interleaved PFCs the standard choice for high-power supplies (kW-class servers, chargers).
Note on the diagram
This page uses a clean schematic of the two-phase interleaved boost PFC; the simulator's waveforms are the exact numerical result. Compare the boost PFC and the bridgeless / totem-pole PFC.
Frequently asked questions
What is an interleaved PFC?
A boost PFC split into two or more parallel legs driven 180° (or 360°/N) out of phase. It gives unity power factor and a regulated DC bus like a boost PFC, plus input-current ripple cancellation and current sharing between the legs.
How does interleaving cancel ripple?
The legs switch half a period apart, so one leg's ripple rises while the other's falls. Adding the currents at the input cancels much of the ripple — for two phases it can drop to a quarter, and to zero at 50% duty — and the effective ripple frequency doubles.
What is phase shedding?
At light load the controller turns off one leg so the remaining leg runs at a more efficient operating point. As load rises the second leg is switched back on. This keeps efficiency high across the whole load range.
Does interleaving change the output ripple?
No. The low-frequency 100/120 Hz DC-bus ripple still follows ΔVo = Po/(2·ωline·C·Vo). Interleaving reduces the high-frequency input-current ripple, not the line-frequency output ripple.