Does anyone know why TOPswitch is so popular? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: July 08, 2023, 04:25:21 pm
content: Hi,We are doing a 20W offline flyback. (FSGM0565 has gone obsolete)We chose the thick-bodied TOP256GN alternative because it is the package that our contractor thinks he can heatsink easiest to our setup. Power integrations don’t do ceramic TO220 like the FSGM0565.Anyway, we now find that TOP256GN is not supported by their PI Expert or PI Designer.We also realise that TOP256GN is a voltage mode controller. We are fixed to a certain transformer, of which much stock has been bought.At 90VAC in, the TOP256GN flyback will go into CCM……and it’s a voltage mode controller….the two together mean more issues with feedback loop….because power integrations don’t seem to provide the modulator transfer function of TOP256, so how are we supposed to do the feedback loop calculation?Not only that, but the TOP256GN needs us to supply the 2-8mA of controller bias current via the feedback optocoupler (!)…..this itself creates issues with opto CTR when hot or aged.You can add a NPN in with the opto, Darlington style, to reduce the opto current...but you then have a wide toleranced NPN gain in your feedback loop...which is in voltage mode...Also, the UVLO pin of the TOP256 is highly sensitive with a 4MEG resistor feeding into this sensitive UVLO pin…more issues that we don’t need.Not to mention the fixed peak current limit which you cannot accurately vary.Also, the TOP256GN has a big load of hysteresis on the uVLO pin...so the part runs down to too low an input voltage.Also, our primary peak current at max load , min vin, is just 0.82A...(to give 20W)...but the TOP256G forces us to have its 1.45A peak current........that corresponds to 43W of power output (for a 20W SMPS)...so our flyback is not even going to know its overloaded till its shipping >43W.......its going to well overheat.....and not go into overload protection.......who buys these TOPswitchs?Does anyone know why power integrations TOPswitch chips are so popular?I do like their Innoswitch, but would want it without the sync rect driver, and would just add the “hack” components so that you don’t have to have such a high NP/NS in certain cases. (to protect the sync rect sense pin). But innoswitch eSOP package is wrong for this job.Also, the TOPswitch starts up when its input goes above the UVLO level....but once thats happened, the UVLO level plummets by 44%...that is ridiculous...no-one wants to operate at a voltage 44% below what is the startup voltage...its going to result in overheating of the SMPS.Can anyone give any reason why we shoudlnt just use a standard Flyback PWM chip with external ceramic TO220 FET?

author: fourtytwo42
author_rank: Super Contributor
timestamp: July 08, 2023, 05:52:29 pm
content: Quote from: Faringdon on July 08, 2023, 04:25:21 pmI have heard it is because you are banned from there forums

author: floobydust
author_rank: Super Contributor
timestamp: July 08, 2023, 06:43:29 pm
content: TOPSwitches are pretty good single chip SMPS, economical. Very complicated under the hood- patents, state machine, multi-function pins, 50 page datasheet - they have a lot of IP inside and are targeted for cookbook consumer power levels and functionality.You are doing it wrong- you design to the IC, not plop the IC in your circuit's whims. And you have already bought transformers?Uh, what comes first - functioning prototype or the component orders for the build?Learning the proper design process would make your life a lot easier. When you jump around and do this and that out of sequence, it makes for a train wreck.Or come to the EEVblog and blame the IC, yeah that's the problem no it's the IC manufacturer yeah that's the problem.Many other companies make single IC SMPS so get off your lazy ass and look at them. ST, On-Semi etc. all have offerings. TOPSwitch is not the only player in town.

author: Gyro
author_rank: Super Contributor
timestamp: July 08, 2023, 07:15:20 pm
content: Quote from: Faringdon on July 08, 2023, 04:25:21 pmCeramic TO220 pkg? What is this rubbish that you speak?

author: ebastler
author_rank: Super Contributor
timestamp: July 08, 2023, 07:29:59 pm
content: Quote from: floobydust on July 08, 2023, 06:43:29 pmLet's be fair here. Faringdon described in the original post that this is an obsolescence-driven project. Presumably the client has bought plenty of transformers for use in a FSGM0565-based power supply and has not paid attention to the core IC becoming obsolete. Which is stupid, but not something we can blame the Faringdon for.So this particular project is indeed a bit backwards, in that the task is to find an IC (and a circuit) which works with the given transformers. Whether or not that is a meaningful approach will probably depend on the quantity and price of those transformers in stock...

author: mariush
author_rank: Super Contributor
timestamp: July 08, 2023, 08:35:57 pm
content: Well, customer should probably order as much of that controller as can still be bough and scrap the rest of the transformers, have them crushed down for copper recovery.Rochester has 800 pieces :https://www.digikey.com/en/products/detail/rochester-electronics-llc/FSGM0565RBLDTU/15645417and 795 here :https://www.digikey.com/en/products/detail/rochester-electronics,-llc/FSGM0565RBLDTU/12611203flip electronics also has 800+ :https://www.digikey.com/en/products/detail/flip-electronics/FSGM0565RLDTU/15861539avnet says rochester has 27k in stock :https://www.avnet.com/shop/us/products/onsemi/fsgm0565rldtu-3074457345628512696It's not ceramic it's plastic covered to-220...

author: wraper
author_rank: Unknown
timestamp: July 08, 2023, 08:42:06 pm
content: Doesn't he mean TO-220 with a die on ceramic insulator which is most common for triacs? Although FSGM0565 is just a usual TO-220F with plastic insulation.

author: Faringdon
author_rank: Super Contributor
timestamp: July 08, 2023, 10:43:52 pm
content: [URL unfurl="true"]https://www.onsemi.com/pdf/datasheet/fsgm0565rb-d.pdf....as you see above, it has Rthj-c of 3 degc/w , which isnt far off metal tab to220, so it surely cant be just plastic?

author: floobydust
author_rank: Super Contributor
timestamp: July 09, 2023, 02:06:33 am
content: EOL last shipments July 2019 four years ago? Driven byFairchild (On-Semi) $175M lossof a 15 year long patent lawsuit to Power Integrations.60-80W output TO-220-6 for a 20W switcher? Why? The IC and package/heatsink are overkill for 20W output and thus the current-sense limit is too high. Good luck.

author: wraper
author_rank: Unknown
timestamp: July 09, 2023, 08:29:36 am
content: Quote from: Faringdon on July 08, 2023, 10:43:52 pmIt's about right for usual plastic TO-220F. Here is examplehttps://www.mouser.com/datasheet/2/149/FDPF39N20-348339.pdf0.5oC/W for TO-220 variant and 3.4oC/W for TO-220F.