Thanks, that’s a great video.
Bridgeless Totem pole PFC…
https://www.youtube.com/watch?v=Jv2JVorAeiE&feature=youtu.beThe above youtube video on BTP-PFC certainly mentions a number of problems with the BTP-PFC.
Interestingly, at 10:00 onwards, they state that overall diode losses for a conventional Boost PFC amount to around 1.3% at 240VAC.
So for a 3kW supply , you are saving around 40W with a BTP-PFC…..so that’s certainly welcome to take that dissipation away from inside the enclosure.
if you draw the ckt and work out which nodes are jumping up and down at HF w.r.t. neutral and or the output 0v line - you will see the problem.
….Interestingly, the above video does not mention the particular EMI problem involving those nodes which jump up and down at high frequency with respect to the neutral and/or the 0V line. The video does however, mention the common mode EMC problem involving the neutral flipping from PFC_POS to PFC_NEG instantly forcing the entire PFC bus to make a common mode leap.
….at 34:16 of the video, it mentions this problem, and says that it can be mitigated by implementing a special soft-start in the slow FETs every time the supply crosses through zero.
The video goes on to talk about reducing switching losses in the BTP-PFC by operating it in Boundary conduction mode and using ZVS…..the problem is, this reduces turn-on switching losses, but increases turn-off switching losses…so its not all good.
Also, the video states that the BTP-PFC offers no size reduction compared to conventional Boost PFC.
There are also the more obvious problems with sensing of current and line voltage. Along with the high side drives etc. The high-side slow FET obviously need an isolated high side supply for the driving of its gate.