What do you use for a 2kW Step down (Vin = 390V) - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: October 15, 2022, 10:43:56 pm
content: Hi,As we all know well, the time-served and legendary , super well known method to get PFC’d high vout (15kv+) from a mains input, (at lets say 2Kw) is to use a Boost PFC…then have a variable vout “Buck converter” fed from the 390V Boost PFC output….this provides the input to an open loop LLC converter. The Buck Vout is regulated such that the LLC vout is effectively regulated.Knowing this….what would you use for the “Buck converter”…(its vout will be 390V to 100V)........which one of these do you use?...1…Several DCM bucks in parallel2….One Big CCM Buck.3…One Phase shift full bridge converter.4…One standard Full Bridge converter5...Two Cascaded dual bucks in parallelAs we all know, such high vout (15Kv) virtually ensures that LLC is the only candidate here…since the transformer leakage will be high…and this can be integrated into the LLC transformer naturally.

author: Wolfram
author_rank: Frequent Contributor
timestamp: October 26, 2022, 11:43:35 pm
content: It all depends on the expected output control range and demands for load regulation and minimum output power. A buck gives control down to zero which is very nice. PSFB does the same, and for cases where you have a regulated input voltage and a narrow load range then frequency control can work well, since your topology is resonant anyways on account of transformer parastics. Sizing of the buck depends on the output voltage range over which you need to provide 2 kW, without a full set of specifications it's a waste of time to try to give exact advice, but I would heavily lean towards a single section CCM buck using a 650 V SiC JFET cascode for reasons of efficiency and simplicity. You can even flip the buck upside down and have your load tied to the common positive to avoid the need for a high-side driver in this stage.With HF HV transformers, the reflected secondary capacitance is often as big of an issue, or a bigger one than your leakage L. For this reason, topologies which incorporate both the leakage L and secondary C are the most common, like parallel-loaded series resonant and LCC.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 27, 2022, 01:31:37 pm
content: Have you considered a buck or buck/boost PFC design?

author: jonpaul
author_rank: Super Contributor
timestamp: October 28, 2022, 09:08:43 pm
content: Bravo to Farrington / treeze for yet another time sink thought experiment.Hummm, 2kw/15kv= 150 ma,load ? application? fault protection ? your liability insurance for a lethal device?Farrington, please inform us exactly who shall design, prototype and manufacture the 390v to 15 kV transformers?I suspect no-one.Just another Farrington rabbit hole.Please find another way to waste your time, without wasting ours.j

author: Bud
author_rank: Super Contributor
timestamp: October 28, 2022, 09:17:30 pm
content: Nikola Tesla would have hard time posting on this forum

author: Simon
author_rank: Unknown
timestamp: October 29, 2022, 09:19:50 am
content: I'm totally confused, I thought the input was 390V. I'm sure you can get off the shelf 100V (96V with a trimming to take it to 100V) power supplies that are active power factor corrected. 2 of these:https://uk.rs-online.com/web/p/switching-power-supplies/1970435in parallel? note I have not checked if they can work in parallel.