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ULN2803 on a propeller — Parallax Forums

ULN2803 on a propeller

AnubisbotAnubisbot Posts: 112
edited 2007-11-02 17:37 in Propeller 1
Hi, i want to switch and dimm some led cluster.
The led cluster will use 450 mA and will run on 12V.
I want to use the Propeller and a ULN2803 Eight Darlington Array ic .
Now my question can the ULN2803 be driven in PWM by the 3.3V of the Propeller ?
And do i need a resistor from the prop to the ULN2803 inputs ?

Thanks
AnubisBot

Comments

  • PJAllenPJAllen Banned Posts: 5,065
    edited 2007-05-13 18:46
    The ULN2803 ICs have built-in limiting resistors, so no additional resistors are necessary.· However, the 3.3V Propeller may be on the ragged edge.· It wouldn't hurt to try.· I suspect that it will work just fine.· The PWM is OK, too.
  • AnubisbotAnubisbot Posts: 112
    edited 2007-05-13 18:51
    Thank you for the quick answer..
    i will give it a try and will post here the results.

    Anubisbot
  • tekochiptekochip Posts: 56
    edited 2007-05-14 14:29
    I'm using the `2803·for an LED driver and a switch driver.· The saturation voltage depends upon how much current you need to pull through the driver.· The spec. sheet says you can pull 300mA with a 3V input.···

    The `2803·drops a fair amount of voltage, but they're really bullet proof for interface to the outside world where ESD will destroy your best efforts.··You can·also use hefty traces at the pins to help as a heat sink.
  • AnubisbotAnubisbot Posts: 112
    edited 2007-05-17 16:16
    Hi, so here is my information update.

    I got my parts and had to find out that it dosent work out, 3.3V is not working.
    So i will have to loock for some other parts.

    Anubisbot smhair.gif
  • tekochiptekochip Posts: 56
    edited 2007-05-17 16:43
    Did you try it with a small load first?
  • whickerwhicker Posts: 749
    edited 2007-05-17 23:19
    The key is using the correct component for what you want to accomplish.
    Are you attempting to switch a single 12V output off and on, or does this cluster have multiple parallel circuits?
    The ULN2803 is for when you have multiple outputs and want to save space/part count.

    If it is a single series circuit, would it kill you to use a normal transistor or mosfet?
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2007-05-17 23:31
    A common mistake/misunderstanding is to use the '2803 as a voltage source like CMOS/TTL gate.· The outputs are·"open collector", current sinks.

    Update: Each '2803 output is protected with its own "free-wheeling" (counter-EMF, et al.)·diode -- ideal for inductive loads.

    Post Edited (PJ Allen) : 5/18/2007 12:12:10 AM GMT
    2803.jpg
    374 x 318 - 22K
  • NewzedNewzed Posts: 2,503
    edited 2007-05-17 23:32
    If your load is inductive in any way, you can use a TIP120 Darlington transistor.·

    Sid

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  • AnubisbotAnubisbot Posts: 112
    edited 2007-05-18 00:53
    No space is not a pronlem, and i just tried a mosfet 30V 1.7A and it works well. with no extra circut.

    Anubis BOT
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2007-05-18 01:59
    I'd sure like to see a schematic of the circuit that you tried using the '2803 as well as the FET.
  • AnubisbotAnubisbot Posts: 112
    edited 2007-05-18 02:58
    with the 2803 i had the schematic that you have in the previous post, but with out the resistor tied to 5V.
    Now i get it, the 2803 would work, but i have to tie the pin to 5V and then it lights up.

    With the mosfet i just have it from the propeller pin to the Mosfet, i know i shoud tie the line to ground.

    Anubisbot
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2007-05-18 11:28
    I used that drawing because of the common misunderstanding in the use of the 2803.· Where it's shown connected ("pulled up") to +5, in your case it should be to +3V (+3.3), VDD.
  • SteelSteel Posts: 313
    edited 2007-11-01 23:28
    How did this problem get resolved?

    I am doing a similar thing and came across this thread in a search.

    I was also going to do just what PJ Allen suggested *not* to do.· Thank you PJ.

    I have a Matrix of 8x16.· I have Shift registers(74595) to control them (1 controlling row, 2 controlling column). The 8 Row connections are Anode and the 16 column connections are cathode.

    I *was* going to have a ULN2803 Darlington Array on the outputs of the 74595 connected to the 8 Anodes of the LEDs.· Apparently this won't work.

    What transistor set should I have on the output of the 74595's to supply enough current for 16 LEDs? (1.5A)

    Thanks
    Shaun
  • GameHackerGameHacker Posts: 15
    edited 2007-11-02 12:42
    I once did an LED matrix product.· I used a ULN2803A to supply 'Ground', and an L293D to supply +V to the led's.· Both of these can be driven from a '595.

    The L293D·only has 4 channels, but can supply enough current.
  • SteelSteel Posts: 313
    edited 2007-11-02 17:37
    Cool. That looks like the ticket! Thanks Gamehacker!
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