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  1. Replies
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    477

    Closed: Re: BJT V(ce) ON in common emitter mode

    thanks , i appreciate that if a NPN in CommEm has <0.3v across its Collec-Emit (what we want), then it is going to be saturated......thing is, we find ourselves having to look at hfe, to see if it...
  2. Closed: Re: Passing radiated EMC with an SMPS involves an element of luck...how much agree?

    Thanks, sorry i mis-worded, i meant that whilst one is doing the design and PCB, there's no fixed way of caluclating what radiated emissions combating components are needed


    Thanks, I have worked...
  3. Closed: Passing radiated EMC with an SMPS involves an element of luck...how much agree?

    I once worked with one of the UK’s finest SMPS design engineers. They were working for the same company as myself at the time. They had already designed many of the SMPS PSU’s as used by the...
  4. Closed: Re: 1 minute vs 1 second isolation voltage test for isolated offline SMPS transform

    Thanks, is their any way for us to know how they did the hi-pot test on the mains transformer in the power supply?
    Ie what voltage time and current setting for the hi-pot test?

    We wish to remove...
  5. Closed: Small high voltage rated mains common mode chokes not available offTheShelf

    Hello,
    A contractor has provided us with a prototype product which is very good quality. It is an offline, non-isolated , SMPS LED driver of 10W. It has no metal shielding and is in a plastic...
  6. Replies
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    477

    Closed: Re: BJT V(ce) ON in common emitter mode

    thanks, we have BJTs with very very little base current in them (to save energy)....and we wonder if there Hfe will always be big enough to get them to turn on fully and have a vce(on) of <0.3v.
  7. Replies
    15
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    477

    Closed: Re: BJT V(ce) ON in common emitter mode

    Is there any situation , where literally any SOT23 or SOT323 NPN with VCE voltage rating of <65V may suffer a drop in Hfe down to less than 15?...surely such a situation simply does not...
  8. Replies
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    Closed: Package Marking for ST25DV04K-IER6S3

    Hi,
    Do you know what is the package marking for the SO8N version of this chip?
    The datasheet doesnt say...
    https://www.st.com/resource/en/datasheet/st25dv04k.pdf

    We have some with package...
  9. Closed: Re: 1 minute vs 1 second isolation voltage test for isolated offline SMPS transform

    thanks, all we want to do is repeat the same hi-pot test that Philips did for their approvals testing, to be sure that the power supply has sufficient isolation. But from the datasheet, there is no...
  10. Closed: Re: 1 minute vs 1 second isolation voltage test for isolated offline SMPS transform

    Thanks, but we notice that IEC61558 isnt mentioned in the datasheet
  11. Closed: Re: 1 minute vs 1 second isolation voltage test for isolated offline SMPS transform

    Thanks very much..

    We are wondering what kind of isolation test the following power supply is spec’d to?…..
    It’s the Philips Xitanium Xtreme 75W LED driver…..AKA…
    “Xitanium 75W 0.35-0.70A GL...
  12. Replies
    15
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    477

    Closed: BJT V(ce) ON in common emitter mode

    Hello,

    For an FMMT491A BJT with 2.7mA flowing into its base and set up in common emitter mode….is there any set of circumstances (temperature, i(ce) etc etc) which might ever result in its...
  13. Closed: Re: 1 minute vs 1 second isolation voltage test for isolated offline SMPS transform

    Thanks.
    It is strange to me that power integrations, on their design software, only ever design the isolated flyback transformers to 3000vac for 1 second (thats for 200-265vac input).
    (screenshot...
  14. Replies
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    309

    Closed: Whats the best way to ESD damage a PCB

    Hi,
    We have an SMD PCB for lighting...and we wish to ESD damage it....how may we best do this....i rubbed one over carpets and ran up and down stairs with it in my hand, and held it while i madly...
  15. Closed: Using TL431/OPTO feedback with LNK304 based HV Buck

    Hi,
    For HV Buck using LNK304 as on page 6 of datasheet (2nd schem down)...

    LNK304 datasheet
    http://www.mouser.com/ds/2/328/lnk302_304-306-179954.pdf

    ...Is their any reason that we cant use a...
  16. Closed: Re: 1 minute vs 1 second isolation voltage test for isolated offline SMPS transform

    The 3mA is the limit value for the leakage current that may flow when under the 3750vac stress for the given time....any more than 3mA flows and its a fail.
  17. Closed: 1 minute vs 1 second isolation voltage test for isolated offline SMPS transformer

    Some offline transformers are spec'd for 3750vac for 1second (3mA).
    Some are spec'd for 3750vac for 1 minute (3mA).

    Generally, which applications require 1 minute?

    ..is it mostly industrial...
  18. Closed: Re: Is FET operating withinin SOA?...Pulsed linear regulator

    Thanks woops sorry i realise the current scale doesnt show on the top post's waveform, here it is re-attached.
  19. Closed: Is FET operating withinin SOA?...Pulsed linear regulator

    Hello,
    We have the following waveform in the STD1NK80Z FET (DPAK). It recurs every 10ms as shown.
    We need to know if this violates the SOA.
    To me, these pulses equate to repetitive pulses of [45V...
  20. Replies
    3
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    631

    Closed: Conducted EMC equipment for 60W offline PSU

    Hi
    Do you know of any cheap place in UK or Europe where we can take our offline PSU for conducted EMC testing?....it doesnt need to be a properly accredited lab.....we just want to use the kit to...
  21. Closed: XC8 C delays for PIC micros not right timing

    Hi,
    When i program a PIC16FXXXX with XC8 , it doesnt give the right delay time
    __delay_(20m) gives 80ms or sometimes 160ms delay.
    Do you know why?
    Also, the program goes wrong if i put in too big...
  22. Closed: Small transformer not useful for offline Flyback useage due to creepage problem

    Hi,
    The E13/7/4 Horizontal Bobbin by Epcos is not suitable for isolated offline Flybacks. This is because the secondary pins are less than 5mm away from the coils of wire as they will lie on the...
  23. Closed: Re: Modifiying an offline LED driver PCB with EMC components on "flying wires"

    Thanks, being able to wire in a proto AC filter board to the main pcb, in order to try and trial out different filter components is of immense value.......so i think we will do a trial where we...
  24. Closed: Re: Modifiying an offline LED driver PCB with EMC components on "flying wires"

    Another point is that many isolated offline SMPS’s have Y Capacitors across the isolation barrier on both sides of the transformer. Do you agree that this acts to further reduce common mode...
  25. Closed: Re: Modifiying an offline LED driver PCB with EMC components on "flying wires"

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Another point is that we would like to experiment with different values of diff mode inductors. As such, how good (or bad) a practice would it be to have these diff...
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