Shop OBEX P1 Docs P2 Docs Learn Events
interfacing uP with optoisolators — Parallax Forums

interfacing uP with optoisolators

homosapienhomosapien Posts: 147
edited 2011-04-09 11:57 in General Discussion
I am using a prop to drive some 12v relays that will in turn control an electric winch. Because I have in the past had mind-boggling issues with noise in circuits introduced by bigger electric motors, I am planning on isolating the 12v motor circuit from the prop power supply (ie no common ground between the two).

I have some optoisolators on hand (Vishay CNY65), but the output of the CNY65 is limited to ~50mA and my relays require ~160 mA. I also happen to have some ULN2803's (Darlington array) on hand, so I will probably end up driving the 2803's with the CNY65's.

This method of driving the larger loads seems a little kludgy, so I took a look on the internet to see if I could find some optoisolators that would drive bigger loads, but almost all seem limited to very small output currents/powers. Is there a reason for this? Does anyone have a source of optoisolators that can drive a decent load (~2W)? Is there a better way to go from a prop pin of 3.3v @ low mA to 12v @ 100's of mA?

Thanks for any suggestions.

Comments

  • PJAllenPJAllen Banned Posts: 5,065
    edited 2011-04-09 07:26
    Then you should get Solid-state relays, the type for DC outputs.
    The AC-output variety abound, but the DC sort can be found.
    They are not interchangeable.

    PE - Looking forward to all of the "opto-isolation theists" chiming in!

    PPE - Looky, looky -- http://www.mouser.com/ProductDetail/Crydom/MP240D4/?qs=KoN42VEC627BeID3bJUbLA%3d%3d
    Bear in mind their caveat: "Images are for reference only
    See Product Specifications "
  • homosapienhomosapien Posts: 147
    edited 2011-04-09 07:48
    PPE - Looky, looky -- http://www.mouser.com/ProductDetail/...D3bJUbLA%3d%3d

    Yikes! At $20 a pop, maybe my kludge is not so bad after all....

    I guess I was thinking that this sort of voltage/current translation with isolation must be needed all the time and I was surprised that there were not some single chip IC's (ie cheap) to fill the need...Even the optoisolators that have a built-in Darlington do not have a very high power rating....
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2011-04-09 07:55
    As Kris Kristofferson sang it, "Nothing ain't nothing, but it's free."
    Switching a power transistor with a photo-transistor isn't "kludgy",
    making a wheelbarrow into a lamp is.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-04-09 08:05
    This looks like something that could handle your load:

    -Phil
  • homosapienhomosapien Posts: 147
    edited 2011-04-09 10:43
    Thanks for your replies guys. I was just making sure that I was not overlooking some common knowledge solution unbeknownst to me.

    Was hoping for some dirt cheap solution in a 4 or 8 device package, but I guess I will keep dreaming...
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-04-09 11:04
    Heres'a a quad device for $3.08 with a 160 mA capacity:

    BTW, DigiKey's search function is your friend for stuff like this.

    -Phil
  • kwinnkwinn Posts: 8,697
    edited 2011-04-09 11:57
    homosapien wrote: »
    Thanks for your replies guys. I was just making sure that I was not overlooking some common knowledge solution unbeknownst to me.

    Was hoping for some dirt cheap solution in a 4 or 8 device package, but I guess I will keep dreaming...

    There are opto isolators with 2 and 4 to a package. I have not come across one with 8 in a package but they may exist. Two quad opto isolators and a ULN2803 could drive 8 relays and would not take up much board space.
Sign In or Register to comment.