Shop OBEX P1 Docs P2 Docs Learn Events
Driving a darlington array — Parallax Forums

Driving a darlington array

w4fejw4fej Posts: 264
edited 2010-10-13 09:45 in Propeller 1
Looking at the data sheet for the ULN2803A it appears (to me) that I can drive this device directly from the Prop. Am I right??

Mike B.

Comments

  • LeonLeon Posts: 7,620
    edited 2010-10-12 14:39
    It should be OK with a 3.3V CMOS input, according to the data sheet. I've got some I was intending to use for a similar application.
  • PavelPavel Posts: 43
    edited 2010-10-12 14:50
    w4fej wrote: »
    Looking at the data sheet for the ULN2803A it appears (to me) that I can drive this device directly from the Prop. Am I right??

    Mike B.

    It does work. I have a board that uses ULN2803A to drive a 12V stepper and the ULN2803A is driven directly from P8X32A.
  • w4fejw4fej Posts: 264
    edited 2010-10-12 14:53
    Ok thanks guys. I suspected it would be ok as we are driving the base of an NPN.

    Mike B.
  • kwinnkwinn Posts: 8,697
    edited 2010-10-12 15:03
    You should still use a current limiting resistor between the prop pin and the uln. The two diode drops of the darlington pair are only approximately 1.4V leaving 1.9V for the prop output driver to drop if there is no resistor.
  • JonnyMacJonnyMac Posts: 9,208
    edited 2010-10-12 15:07
    Yes, just make sure you do in fact use the "A" variant (ULN2803A) as it has the required series resistor in the base of the Darlington circuit.
  • kwinnkwinn Posts: 8,697
    edited 2010-10-12 15:12
    Oops - time to get an updated data sheet.
  • tonyp12tonyp12 Posts: 1,951
    edited 2010-10-12 16:17
    here is some good reading:
    http://www.parallax.com/dl/docs/cols/nv/vol1/col/nv6.pdf

    http://oomlout.com/8TRA/8TRA-Guide.pdf
  • godzichgodzich Posts: 74
    edited 2010-10-13 05:47
    Hi,

    Using ULN2803 (with or without A) - you should NOT add any series resistance. With 3.3Volts on the input to the Darlington array you should be able to load te output with at least 300mA.

    I would recommend that you use ULN2003 instead. Its so much cheaper, albeit it only has 7 drivers in one package! But usually you can buy 3 pieces of ULN2003 for the price of one ULN2802.

    Christian
  • tonyp12tonyp12 Posts: 1,951
    edited 2010-10-13 06:36
    The extra cost it not that great, so if you need 8 gates and I'm sure there are other differences too.

    Mouser Part #: 595-ULN2803AN
    1: $0.94
    25: $0.76
    100: $0.666

    Mouser Part #: 595-ULN2003AN
    1: $0.57
    25: $0.42
    100: $0.36
  • godzichgodzich Posts: 74
    edited 2010-10-13 07:02
    Hi,

    ULN2003 and ULN2803 differs only in number of darlingtons (7/8) and number of pins. The drivers inside are the same! It seems that the Mouser pricing is such that if you look at the price per driver, you pay the double of getting only the eighth driver.. Not a bargain, but at these prices and small quantities, who cares...

    tonyp12 wrote: »
    The extra cost it not that great, so if you need 8 gates and I'm sure there are other differences too.

    Christian
  • w4fejw4fej Posts: 264
    edited 2010-10-13 09:45
    tonyp12 wrote: »
    here is some good reading:
    http://www.parallax.com/dl/docs/cols/nv/vol1/col/nv6.pdf

    http://oomlout.com/8TRA/8TRA-Guide.pdf

    Love the Johnny Mac article. That's all the info I Need.

    (Jonny Mac. Is your picture meant to intimadte folks?? :smhair: lol)

    Mike B.
Sign In or Register to comment.