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Fast but small optocouplers?

Discussion in 'Electronic Design' started by Joerg, Sep 1, 2012.

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  1. Joerg

    Joerg Guest


    A bit much in quiescent current and very pricey but they sure are fast.
    However, one has to be careful. Several clients have been burned by
    fancy new-tech isolator chips (not from NVE though). In all cases the
    comeuppance happened at the EMC test facility.
     
  2. Joerg

    Joerg Guest

    Thing is, I've only got a (somewhat) regulated 10V on that side and not
    much power. A milliamp or two. So that'll add more parts.
     
  3. Joerg

    Joerg Guest


    That's CM rejection, not an important parameter here.
     
  4. What about spiral turn PCB transformer, the prepreg constitutes approved isolation between the two turns. Needs HF (above 10MHz) though due to low magnetizing inductance if you need it that small

    Cheers

    Klaus
     
  5. Joerg

    Joerg Guest

    That works. But it would make EMC a challenge. I'll try the opto thing,
    looks like the Sanyo couplers might do the job. If not then I guess
    it'll have to be a transformer. Or maybe an ultrasound piezo transfer,
    that would be really high tech :)
     
  6. Joerg

    Joerg Guest

    The Sanyo is fast enough, so most likely I'll use that one.
     
  7. Tim Williams

    Tim Williams Guest

    Cute! It's a miniature SFH6345 (which is, in turn, a 6N136 without the
    base pin...and its pesky capacitance). That'll come in handy for IGBT
    drivers!

    Hmm, offhand, Digikey and Mouser don't stock it.. will have to look
    around.

    Tim
     
  8. spamtrap1888

    spamtrap1888 Guest


    Did you look at this one? They tout it as a pulse transformer
    replacement:

    http://www.avagotech.com/docs/AV02-1302EN
     
  9. Tim Williams

    Tim Williams Guest

    The ones from Analog brag about their active refresh, which makes sure
    that, if they flip, they flip back to the correct state within some period
    of time.

    We've used them (the ADI parts) with MOSFET drivers, where the dV/dt
    pushes the datasheet limits. We haven't seen them chatter at all.

    Tim
     
  10. Tim Williams

    Tim Williams Guest

    I have full right to insult anything that breaks!

    Resistors aren't necessary with these types, and taking it out to a pin is
    far more detrimental in typical applications: big edges really screw them
    up.

    Note carefully, for example, how Fairchild rates the dV/dt of their 6N136.
    http://www.fairchildsemi.com/ds/6N/6N135.pdf
    The dV/dt could be 1 or 100kV/us and it won't matter, the charge injection
    isn't even enough to turn on the transistor at a mere 10Vpp. Terrible
    liars. Other manufacturers rate theirs at only 1kV/us, though still a 10V
    edge. Compare that to the SFH6345, which is rated over 10kV/us (by any
    manufacturer), and tested with a 1kVpp edge (Avago tests theirs at
    1.5kVpp!).

    As for empirical results, a 6N136 will do this in a gate driver:
    http://t3sl4.dnsdynamic.net/Images/Induction902.jpg
    The full waveform is,
    http://t3sl4.dnsdynamic.net/Images/Induction901.jpg
    which as you can see isn't very much delta V or delta T as gate drivers
    go. A little shielding wrapped around the 6N136 got it working up to
    320V, but I still don't trust it. And the shield reduces the peak voltage
    rating in a non-approved manner.

    Tim

    P.S. Mmmm, Sprecher Abbey Triple. Geez, some fruit flies got in through
    the window, they're curious about it. Heck, I would be too. Now where's
    the fly swatter...
     
  11. Tim Williams

    Tim Williams Guest

    I have full right to insult anything that breaks!

    Resistors aren't necessary with these types, and taking it out to a pin is
    far more detrimental in typical applications: big edges really screw them
    up.

    Note carefully, for example, how Fairchild rates the dV/dt of their 6N136.
    http://www.fairchildsemi.com/ds/6N/6N135.pdf
    The dV/dt could be 1 or 100kV/us and it won't matter, the charge injection
    isn't even enough to turn on the transistor at a mere 10Vpp. Terrible
    liars. Other manufacturers rate theirs at only 1kV/us, though still a 10V
    edge. Compare that to the SFH6345, which is rated over 10kV/us (by any
    manufacturer), and tested with a 1kVpp edge (Avago tests theirs at
    1.5kVpp!).

    As for empirical results, a 6N136 will do this in a gate driver:
    http://t3sl4.dnsdynamic.net/Images/Induction902.jpg
    The full waveform is,
    http://t3sl4.dnsdynamic.net/Images/Induction901.jpg
    which as you can see isn't very much delta V or delta T as gate drivers
    go. A little shielding wrapped around the 6N136 got it working up to
    320V, but I still don't trust it. And the shield reduces the peak voltage
    rating in a non-approved manner.

    Tim

    P.S. Mmmm, Sprecher Abbey Triple. Geez, some fruit flies got in through
    the window, they're curious about it. Heck, I would be too. Now where's
    the fly swatter...
     
  12. Guest

    You claim that everything suggested is too big, but I just wonder, how
    you are going to handle the PCB creapage distances with very small
    (narrow) packages, if you intend to keep the _system_ level insulation
    ratings in the kV range.
     
  13. Nico Coesel

    Nico Coesel Guest

    I've used an Avago HCPL-0631 for a similar situation. Its blazingly
    fast. It does require 5V-ish power on the secondary side. In my case I
    solved that with a simple resistor + zener diode.
     
  14. Joerg

    Joerg Guest

    They hold 21,000 of them right now. Is that not enough stock? :)
     
  15. Joerg

    Joerg Guest

    Partially by potting. I have space, but not as much as needed for a big
    fat HCNW137 chip or the like.
     
  16. Joerg

    Joerg Guest


    Yes, I looked at those. They have the usual problem, a whopping 0.500"
    length. It would be like trying to squeeze a Ford F-350 Crew Cab with a
    full length bed into a parking space for a compact car.
     
  17. Joerg

    Joerg Guest

    But you also had the space for these rather fat IC packages :)
     
  18. Nico Coesel

    Nico Coesel Guest

    It also comes in an SO-8 compatible housing. Its a bit high but the
    footprint is small and it is a dual-opto so the footpring for each
    optocoupler is tiny :)
     
  19. Joerg

    Joerg Guest

    But it's still too big and we only need one.
     
  20. Tim Williams

    Tim Williams Guest

    Weird, I had found the PC457L0NIT0F, which has the exact same datasheet,
    which is the -P0F, not -T0F.

    Digikey has 23k and change of the -NIP0F, and 58k and change of
    the -YIP0F, which is VDE marked. Again, same datasheet and link.

    Now I want to know what the hell is the difference! Nothing about part
    numbering in the datasheet. Sharp's website isn't helpful; datasheet
    specifies "corresponding Optoelectronic Application Notes", but there are
    none listed under this product type. And their listing shows the
    45*6*L0NIP0F, but only the 457 -YIP0F.

    Tim
     
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