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Propeller protoboard 12v? — Parallax Forums

Propeller protoboard 12v?

CrosswindsCrosswinds Posts: 182
edited 2011-08-15 16:46 in Propeller 1
Hello guys!


Is it possible to feed the proto-board with 12v? It says only 6-9. But according to the data-sheets for the regulators, they can take much more. Or am i missing out on something here?

Comments

  • Graham StablerGraham Stabler Posts: 2,510
    edited 2011-08-15 06:52
    I do.

    Graham
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2011-08-15 07:12
    Yes, you are missing something. Linear regulators dissipate heat based upon the input to output differential voltage times the current. If you were to read the datasheet and just go by only two figures, the maximum voltage and the maximum current you would be missing 99% of the datasheet. If you run the regulator at this maximum of 25V in and 1.5A output for instance then the regulator if it could survive (it won't) would be dissipating 30W of energy while burning a hold in your pcb and melting even the solder. I wouldn't be far wrong maybe but it would not work.

    With 12V in and 5V out that's 7V difference times the current when it's just running a little demo will be maybe 10 to 20ma but can climb to over 100ma. That's still okay though even though those regulators are getting a bit warm at just under 1W. Now you want to do something more with it then running a demo and you hook-up a few more things that load up the +5V supply. That's where we wave bye bye to the valiant linear regulator which gave it's all for Prop and Spin.

    It's okay as Graham said but know the limits based upon those other variables that only you know. Parallax specified these voltages because they took into account how the protoboards are used and that all kinds of stuff gets hooked-up to them.
  • CrosswindsCrosswinds Posts: 182
    edited 2011-08-15 09:33
    Yes, you are missing something. Linear regulators dissipate heat based upon the input to output differential voltage times the current. If you were to read the datasheet and just go by only two figures, the maximum voltage and the maximum current you would be missing 99% of the datasheet. If you run the regulator at this maximum of 25V in and 1.5A output for instance then the regulator if it could survive (it won't) would be dissipating 30W of energy while burning a hold in your pcb and melting even the solder. I wouldn't be far wrong maybe but it would not work.

    With 12V in and 5V out that's 7V difference times the current when it's just running a little demo will be maybe 10 to 20ma but can climb to over 100ma. That's still okay though even though those regulators are getting a bit warm at just under 1W. Now you want to do something more with it then running a demo and you hook-up a few more things that load up the +5V supply. That's where we wave bye bye to the valiant linear regulator which gave it's all for Prop and Spin.

    It's okay as Graham said but know the limits based upon those other variables that only you know. Parallax specified these voltages because they took into account how the protoboards are used and that all kinds of stuff gets hooked-up to them.

    Again! Thank you very much for that explanation!

    I think i will be safe then. Because, i will not pull anything more through them than the prop itself and a RTC-clock.

    The need for 12volt is for my ULN circiuts, and those will not feed through the regulators anyway!
  • StefanL38StefanL38 Posts: 2,292
    edited 2011-08-15 10:23
    The voltage-drop across a linear regulator can be reduced if you insert another voltage-regulator with 9V output.

    So the voltage-drop is only 12V-9V=3V and then 9V-5V = 4V. So this might be a good alternative for using two different powersupplies.

    Now a days voltage-regulators use to have a thermal protection.
    This means the voltage (and current) is going down if a limit-temperature is reached. The circuit will get not enough voltage and will not function as long as the temperature is at the limit but the regulator will be protected from burning through.

    Does the datasheet mention anything about thermal protection?

    keep the questions coming
    best regards

    Stefan
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2011-08-15 16:46
    StefanL38 wrote: »
    <snip>

    Now a days voltage-regulators use to have a thermal protection.
    This means the voltage (and current) is going down if a limit-temperature is reached. The circuit will get not enough voltage and will not function as long as the temperature is at the limit but the regulator will be protected from burning through.

    Does the datasheet mention anything about thermal protection?

    keep the questions coming
    best regards

    Stefan
    Thermal protection is standard on regulators but it is not meant for continuous operation as the silicon's characteristics itself etc is affected and the device life is shortened. Of course too it's not much use having the regulator go in thermal protection mode at a certain time of day then kicking in again after it's cooled off, unless it's simply running demo software on the test-bench.
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