Power Integrations website not recomending a sync rect controller for HiperTFS? - Page 1
Forum section: electronics / general

author: opampsmoker
author_rank: Regular Contributor
timestamp: December 29, 2020, 06:12:18 pm
content: Hi,We wish to use HiperTFS controller from Power integrations, but need sync rects with it.I messaged their forum, to ask for recomendations for a secondary side sync rect controller togo with the HiperTFS controller, but my post doesnt get presented there. Is there a limit to how many postsyou can have on the power integrations website?They wont publish my posts any more. Do you know why?HiperTFS controllerhttps://ac-dc.power.com/products/hiper-family/hipertfs-2/******************** EDIT ************************* EDIT *****************************************************EDIT:....OK , PI have now responded in a post about this, and have said that they use SRK2000 synch rect driver....but only in one of their application designs. One!The best situation for a synch rect driver is to actually be able to switch off before the pri fet switches, instead of simply reacting to it switching, which is the modus operandi of the SRK2000 sec side sync. rect. driver.... (so SRK2000 is a "reactive" type sync rect driver, instead of being "predictive"...the Inno switch is superb and is a "predictive" synch rect driver)SRK2000https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwizhc3qqvbtAhXKh1wKHXqKAckQFjAAegQIBhAC&url=https%3A%2F%2Fwww.st.com%...Page 15 of the SRK2000 (synch rect driver used in DER385) datasheet warns that some mosfets will have too much bond wire inductance and will instigate faulty behaviour of the synchronous rectification....and the mosfet may need swapping out......such sensitivity seems very poor, and in fact, indicates that these kind of "reactive" type sec side sync rect drivers are dangerous.Power integrations employ a Superb group of SMPS engineers to make demo boards and eval boards, but it says it all that they have only used a “reactive” type sec side sync rect driver chip on one occasion (DER385). That was the SRK2000 discussed above. (whose datasheet tells of the perils of using it)And in DER428, power integrations use “natural drive” (no chip) sync rectification for a 2TFC with 14A output….but even then only do sync rect for the power diode…not across the freewheel diode.This says it all to me about “reactive” type sync rect drivers. They are plain dangerous. They promise vast reductions in sec side rectification losses, but are too risky. Do you agree?Power Integrations has never tried to make a synch rect driver IC like the SRK2000, and would you agree, that this is because they are very poor and not worth making?The innoswitch of course, coordinates the pri and sec side fets superbly, and so is a brilliant synch rect driver.

author: MK14
author_rank: Super Contributor
timestamp: December 29, 2020, 07:41:34 pm
content: Quote from: opampsmoker on December 29, 2020, 06:12:18 pmI have absolutely, 100% no idea, whatsoever.***Cough Cough cough cough cough ....................................***But, they may not be entirely 100% happy, with your political post(s), possibly knocking China, or whatever, on their professional product Forum website.https://ac-dc.power.com/forum/green-energy-forum/2020/power-integrations-shoudl-instigate-worldwide-take-domestic-power/You didn't say your user name there, but I/we can guess:QuoteHighlights/extracts:It rambles, on and on and on and on ...Like this:Quote

author: Gyro
author_rank: Super Contributor
timestamp: December 30, 2020, 10:46:34 am
content: I just laughed out loud for the first time in days!

author: MK14
author_rank: Super Contributor
timestamp: December 30, 2020, 02:25:02 pm
content: They seem to have deleted (or hidden) the post, now. So, here is a text extract of it:(Bold/font-size added by me, most of menu text removed by me).Title:QuoteQuote

author: opampsmoker
author_rank: Regular Contributor
timestamp: December 31, 2020, 03:59:35 pm
content: Thanks,For a realistic offline 2 Transistor forward converter with synch rects, the attached is the only realistic "modus operandi" to do it.Would you agree?The synch rects get switched off before the primary fets turn ON. There is no chance of reversing output inductor current in light load, as there is a load current monitor which disables the synch rects in cases of light load current.This is backed up by a comparator which looks at the COMP pin of the primary side controller. Whenever this goes low in voltage, indicating light load, then again the synch rects are turned OFF. Thus there is no chance that the synch rect logic could end up keeping the "freewheel" synch rect ON permanently during light load.Do you know why there are no offtheshelf chipsets which incorporate this circuitry?LTspice sim and pdf schem attached