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Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Another thing to consider with the Flyback or Buck-Boost topology is that it will perform automatic PFC inherently in DCM without an active PFC controller.
At 100W you could easily get both the PFC functionality and step down functionality from one supply and one transformer/magnetic part.
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
What sort of output voltage do you need?
Push-pull is a bad topology for high power and high input voltage, due to the significant losses associated with the energy stored in the leakage inductance being dissipated in the MOSFETs on each switching cycle. Half- and fullbridge and two-switch forward (as shown in your initial post) are preferred for higher power and higher input voltage, as they return this energy to the DC bus capacitor.
Goodchild wrote ...
Another thing to consider with the Flyback or Buck-Boost topology is that it will perform automatic PFC inherently in DCM without an active PFC controller.
At 100W you could easily get both the PFC functionality and step down functionality from one supply and one transformer/magnetic part.
Most topologies can do this, if you can live with output current ripple or if you move the bulk storage capacitance to the secondary side.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Wolfram wrote ...
Goodchild wrote ...
Another thing to consider with the Flyback or Buck-Boost topology is that it will perform automatic PFC inherently in DCM without an active PFC controller.
At 100W you could easily get both the PFC functionality and step down functionality from one supply and one transformer/magnetic part.
Most topologies can do this, if you can live with output current ripple or if you move the bulk storage capacitance to the secondary side.
Most typologies can, poorly...
Buck-Boost and Flyback are about the only typologies that can do it effectively with a decently high PF (>0.99) and low THD (<4%).
The bulk storage would have to be on the secondary side anyway or else your PF wouldn't be any better than a bridge rectifier and capacitor solution.
The trade-off is complexity/cost vs efficiency. Half-Bridge/Full-Bridge will provide a more efficient operation at higher cost and parts count with the need for a PFC front end.
Flyback, although less efficient has much lower parts count and no need for a PFC front end. This trade-off will make or break a product. This is why without a doubt the vast majority of PFC consumer SMPSs favor a Flyback like topology.
EDIT: Almost forgot, CUK and SEPIC, can also have decent PFC quality without active PFC.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
- High component count is not a problem. (I want 2 transistors if possible.) - I will use IGBT's for the 120 rectified side. - I'm planning to step down to about-ish 12~18 volts at high current. - I want about 800 to 1,000 total watts at the output.
Ross Allan wrote ...
If you can acquire some GaN HEMTs (eg: TPH3205WS), a totem pole (bridgeless) topology will be more efficient as you don't have any diode drops. Switching losses will be too high with MOSFETs, may also work with IGBTs ( ).
I will look at these.
Flow Chart.
EDIT: (here are the ferrites and powder cores I have to choose from.)
I'm thinking of using the blue powder toroid for the PFC inductor, and the ferrite E cores for the step-down transformer. My inventory is running abit low at the moment.
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Need Help With a PFC and PWM Circuit.
