Electronics > Power/Renewable Energy/EV's
Totem Pole PFC is over-hyped?
Faringdon:
--- Quote ---The synchronous boost rectifier Coss will be dissipated in the boost switch at turn on and the current spike will be a nasty one.
--- End quote ---
Thanks, though a simple delay circuitry would ensure that the boost diode's synch FET only turned on after its diode had been brought into conduction....so thats ZVS pretty much.
--- Quote ----The bridge MOSFET will require measures to protect them from surges. The totem pole PFC has an inductor in series to dissipate some of the surge energy.
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Thanks, the PFC output caps will provide a good deal of surge quenching........as they do with "standard" Boost PFCs.
Standard Boost PFC as you know, most commonly has an inrush diode which shorts out its inducto to the inrush surge, and to any other surges.
Also, there are EMC filter inductors, as well as the MOVs at the front end.
....Yes the Totem does have the inductor upstream to add some more protection, but it will of course saturate when surge current becomes significantly high.
I dont think anyones touting the Totem on the basis of its surge resilience....though yes, i would give you that one to an extent. Though a standard PFC with equivalent inductance added in the way of EMC filter would be the same......and cheaper than Totem which, with all its extra circuitry, is more expensive in general.
I investigated a Totem design for an interview at a big disty near the M25 (you will have heard of them) where they were designing and building totems......the circuitry is way more extensive and expensive than a standard boost PFC........They were of course doing this because their customers were not seeing the benefits of the Totem, so they were attempting to put together totem demo boards so that they could try and show them to the cust....from the questions they were asking me at interview.....it was obvious they were having biggo problems with common mode noise.
--- Quote ---Software: if one is aiming at 100K units or more, software is not an issue.
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So it would be interesting to hear if you believe that the benefit_point for totem is when you can garantee orders of 100,000 per year or more?
There are not that many products that can be sure of sales of 1.5kW SMPS with those volumes....or anywhere near those volumes.
Thanks for the anlysis on FETs for the Mains bridge.....though as discussed, multiple cheap FETs in pllel would be they way round that........with cheap heatsink clips for easy assembly.....or even multiple SMD D2PAK and thermal vias to heatsink......and poss metal bar across the top to give that bit more heat conduction away from the FETs.
temperance:
--- Quote ---Thanks, though a simple delay circuitry would ensure that the boost diode's synch FET only turned on after its diode had been brought into conduction....so thats ZVS pretty much.
--- End quote ---
I'm not talking about MOSFET turn on delays and things. That's pretty obvious. I'm talking about Coss of sync rectifier. This cap is being discharged every cycle and this power is being dissipated in the main switch. That's a substantial loss.
--- Quote ---So it would be interesting to hear if you believe that the benefit_point for totem is when you can garantee orders of 100,000 per year or more?
There are not that many products that can be sure of sales of 1.5kW SMPS with those volumes....or anywhere near those volumes.
--- End quote ---
EV chargers...
--- Quote ---Thanks for the anlysis on FETs for the Mains bridge.....though as discussed, multiple cheap FETs in pllel would be they way round that........with cheap heatsink clips for easy assembly.....or even multiple SMD D2PAK and thermal vias to heatsink......and poss metal bar across the top to give that bit more heat conduction away from the FETs.
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Not really. Two 100mOhm MOSFET's in parallel cost you nearly the same as one 50mOhm MOSFET. Mounting cost increases and stray capacitance too.
Faringdon:
--- Quote ---I'm not talking about MOSFET turn on delays and things. That's pretty obvious. I'm talking about Coss of sync rectifier. This cap is being discharged every cycle and this power is being dissipated in the main switch. That's a substantial loss.
--- End quote ---
Thanks Yes, but the same such happens with the totem pole PFC.
--- Quote ---Not really. Two 100mOhm MOSFET's in parallel cost you nearly the same as one 50mOhm MOSFET. Mounting cost increases and stray capacitance too.
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Thanks, as you know, Stray capacitance of the fets that make the mains bridge synchronous doesnt matter...they switch at 100Hz....and at the zero cross.
--- Quote ---Not really. Two 100mOhm MOSFET's in parallel cost you nearly the same as one 50mOhm MOSFET. Mounting cost increases and stray capacitance too.
--- End quote ---
Thanks, for 3kw PFC with syncd 50hz bridge, i would use four of of these SMD fets on each diode...
IPL60R060CFD7AUMA1......
https://www.infineon.com/dgdl/Infineon-IPL60R060CFD7-DS-v02_00-EN.pdf?fileId=5546d46262b31d2e01633ed634654cdf
each SMD, thermal via'd to the single heatsink, which would be used for all the 16 of them...to make a single sync'd 50hz bridge heatsink assembly.
At 3kw and 90vac, they would worst case dissipate 1.74W each...but thats at 150degc junction.
With volumes in the 100,000's, i'd get them at well under a dollar each.
That would work out no more expensive that a totem pole at 90vac and 3kw.....as you know, totem uses the 4 fets.....two of which have high switching and conduction loss...the other two have high conduction loss. OK , with my 50Hz sync'd thing i have two more fets and a diode (the diode wont conduct much).....but it'll work out cheaper overall than the totem.
I cannot find an example of either Totem or "syncd 50hz pfc" at 3kw, 90vac on the web though.
Its likely that 3kw at 90vac would be served by two 1.5kw pfc's in parallel...whether totem or "50hz sync'd".
I am going to search totem for the fets used in a 90vac, 1.5kw totem.
And of course, they (totem pole pfc's) have far more extensive extra circuitry compared to the "50hz sync'd pfc" type
As seen below, the web examples of 1.5kw totem dont show it at 90vac and 1.5kw...only at 230vac nominal....
1.5kw totem pole pfc:-
--- Quote ---https://gansystems.com/wp-content/uploads/2020/01/Optimal-Design-for-High-Frequency-GaN-Based-Totem-Pole-PFC.pdf
--- End quote ---
So, yes, been looking for some time for a ~3kW (or even ~1.5kW) Totem pole PFC eval board on the web...or an app note on such...but cannot find it.......i believe that the FET situation for totem pole for 3kW PFC for 90VAC input would be very expensive. For 3kW @ 90VAC i believe those two front end HF switching FETs would be well toasted. They usually, ayk, make those GaN type........and they have high switching loss, as well as high conduction loss at 90vac in and 3kW.
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