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Over heating regulator — Parallax Forums

Over heating regulator

InteractivesInteractives Posts: 83
edited 2005-07-28 18:34 in BASIC Stamp
Hello all, Ive got a wee bit of a problem here- I've got my BS2 hooked up to a 9vdc power supply, and am driving a Parallax brand RFID reader off of VDD, wich then triggers one of two relays hooked up to a ULN2803 ( the relays have their own power supply, with common cathode to STAMP). Every thing works ok, but my· on board 5 volt regulator keeps getting really hot to the touch! Any ideas why? I havent been able to find the specifications of the RFID reader, but I dont think it pulls too many amps for the STAMP. Perhaps in combination with the ULN2803?? confused.gif

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-07-21 19:17
    Hello,

    ·· Please list your connections so that we know how everything's connected.· IOW, what is connected where?· =)


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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • ForrestForrest Posts: 1,341
    edited 2005-07-21 19:35
    The RFID reader draws 199 mA when active - way too much for the voltage regulator on the BS2 module. Or are you getting 5V from your carrier board's power supply? A lot of Parallax's carrier board's can supply 1A at 5V DC.
  • InteractivesInteractives Posts: 83
    edited 2005-07-21 19:38
    Forrest, that explains it! I was using the carrier board before, then I soldered everything onto a PCB and it mysteriously started overheating! I suppose I was using the boards power, when I though I was using VDD. Thanks! Do you think I could use a voltage divider circuit tapped off of the 12V VIN to produce my 5vdc?
  • InteractivesInteractives Posts: 83
    edited 2005-07-21 19:39
    Chris tommorow I will be able to attach a bitmapped schematic, but Im borrowing my coworkers computer today...
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-07-21 19:44
    ·· Actually I think you already explained it.· If you're getting power from the Stamp's Vdd line, and powering the Stamp from Vin, then you're definately overloading the Stamp's on-board regulator.· On the BOE or some other boards there is a hefty 5V regulator which can supply up to 1 amp.· But not from the module itself.

    ·· Just out of curiosity, are you powering the RFID, AND the ULN·from the Stamp's Vdd pin?

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • InteractivesInteractives Posts: 83
    edited 2005-07-21 19:52
    actually Im running the ULN off of the same 12v supply that Ive got my relays hooked up to. There gonna be a lot of wall warts stuffed into this one.
  • ForrestForrest Posts: 1,341
    edited 2005-07-21 20:41
    It would be simple to make a 12V to 5V DC power supply. You'll just need a +5V 7805 regulator, a 100uF 35V electrolytic capacitor and a 10uF 35V electrolytic capacitor as shown here www.epanorama.net/circuits/psu_5v.html Note the 100nF capacitor isn't needed if you minimize the distance between the +5V output and the RFID. You can buy all these parts at Radio Shack for a total of $5
  • InteractivesInteractives Posts: 83
    edited 2005-07-21 20:53
    thanks!
  • InteractivesInteractives Posts: 83
    edited 2005-07-27 20:42
    O.K., so I havent got a chance to go out to get the 7805, but I had a LM317T on hand, and it sells its self as a adjustable voltage regulator.I hooked it all up, and stepped down the 12 volts to around 4.87 volts- and voila!! The RFID reader doesnt work. It's on board LED lights up, but it doesnt function. Boo. You mentioned that it needs 199mA- am I wrong in assuming that the RFID reader pulls the amps it needs, and leaves the rest? Seems like I could be wrong about that. I ask because I also tried just using a seperate 5v 500mA max wall wart to rull the thing, and it also didnt work. Do I need a current limiting resistor?I feel like smashing this thing. Boo.
  • ForrestForrest Posts: 1,341
    edited 2005-07-27 21:36
    Did you connect the grounds for the 5V and 12V power supplies and the Basic Stamp together? You'll need to do this to keep everything at the same ground level.
  • InteractivesInteractives Posts: 83
    edited 2005-07-28 13:28
    Ill try that, and report back.
  • InteractivesInteractives Posts: 83
    edited 2005-07-28 13:42
    When I hook the grounds togather the voltage regulator immediatly overheats. I even checked the polarity wih a meter before hand .I baffled.
  • InteractivesInteractives Posts: 83
    edited 2005-07-28 18:05
    O.k., so I broke down and got the 7805- works like a dream! Sometimes ya just gotta go to the shack. Thanks to all for your help.
  • ForrestForrest Posts: 1,341
    edited 2005-07-28 18:34
    Glad you got it working. Concerning your problems with the LM317T - the pinout is different from the 7805. On the LM317T - the ground (reference) is NOT the middle pin like it is on the 7805. I wonder if you had the LM317T connected incorrectly.
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