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Controlling source voltage with a BS1 — Parallax Forums

Controlling source voltage with a BS1

GarthGarth Posts: 18
edited 2008-04-22 12:36 in BASIC Stamp
Ok, I'm still new at this. I need to send source voltage to my load. I've got it working (see schematic) but I can't help thinking there is a more efficient way to accomplish this.

Any ideas and comments are welcome.

Thanks

Comments

  • ercoerco Posts: 20,261
    edited 2008-04-20 21:00
    The very simplest thing would be a 5-volt reed relay like Radio Shack 275-232. It will draw 20 mA (the permissible max from one pin) and switch isolated SPST contacts. Just wire it from any pin to ground and put a reverse diode across it, and you're in business.

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    ·"If you build it, they will come."
  • GarthGarth Posts: 18
    edited 2008-04-20 21:29
    Thanks for the response Erco. I had considered a relay however, i should have mentioned that I need to repeat the circuit 5 time and I also need to keep the foot print as small as possible.

    Thanks again
  • ercoerco Posts: 20,261
    edited 2008-04-21 00:26
    If you're sold on transistor switching, you can probably use a single transistor. Try eliminating your 3904 transistor and reduce your 100K bias transistor down to 330-1000 ohms to switch your 3906 on. TIP31 is a good power transistor with heat sink if you're pulling molto current.

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    ·"If you build it, they will come."
  • Beau SchwabeBeau Schwabe Posts: 6,572
    edited 2008-04-21 03:05
    Garth,
    ·
    Since your voltage supplies are different, using a single PNP transistor won’t work.· You need the NPN in this case as a high-side driver.
    ·
    If you can move your load so that it is happy with one side connected to your 24V supply, then a single NPN transistor solution will work.


    BTW) In your schematic, it looks as though the Collector and Emitter of the PNP are swapped.
    ·
    ·
    ·
    What are the current requirements of your load?·
    That will help determine the correct transistor and resistor values at the transistor base that·you should use.
    ·

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • BartyBarty Posts: 2
    edited 2008-04-21 03:20
    Take a look at ULN2803A - Its a great chip for doing this type of thing. 8 independent channels that hardly no power from the BS to drive it...

    The chip itself doesn't even a power pin on it (Only a single ground)...

    Wire your load directly to the 24Vdc supply and use this device to control the connection to ground...

    As mentioned mentioned, if the load is inductive (like a motor or relay), place a diode across the coil to reduce the "fly back" energy...

    Happy Stamping....
  • David H.David H. Posts: 78
    edited 2008-04-21 13:33
    Garth,
    Also make sure your positive power is connected to VDD and your ground connected to VSS.
    Good luck with the project.

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    David


    There are 10 types of people in this world,...
    Those that understand binary numbers, and those that don't!!!
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2008-04-21 23:16
    Barty said...
    Take a look at ULN2803A ... As mentioned, if the load is inductive (like a motor or relay), place a diode across the coil to reduce the "fly back" energy...
    Actually, the ULN2803 has the protective diodes built in and·pin 10 should go to +V.· [noparse][[/noparse]Though often mistake for one, Pin 10 is not·a power pin.]

    Note -- These "gates" (having "open collector" outputs) are for sinking current, not sourcing voltage.

    attachment.php?attachmentid=51824

    Post Edited (PJ Allen) : 4/21/2008 11:21:58 PM GMT
  • kingspudkingspud Posts: 128
    edited 2008-04-22 00:09
    Just a heads up!

    There is a great chip out there by the name:

    UDN2981

    http://www.datasheetcatalog.com/datasheets_pdf/U/D/N/2/UDN2981.shtml

    It is an 8-channel source driver chip.

    You have 8 input points that can you put 5 volts into and then you can put 15 volts into the 2981, which in turn drive 15 volts out of each 8 outputs.

    Check it out, it might work for you,

    Joe

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    Albert Einstein
  • BartyBarty Posts: 2
    edited 2008-04-22 00:36
    WHERE HAS THIS CHIP BEEN ALL OF MY LIFE - I could have used this years ago!

    Thanks kingspud!

    Great matching/pairing device to the 2803...
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2008-04-22 12:36
    http://forums.parallax.com/showthread.php?p=722464
    ·
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