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BoE Supply Voltage? — Parallax Forums

BoE Supply Voltage?

adengleadengle Posts: 2
edited 2007-03-11 21:49 in BASIC Stamp
Hey gang...probably a very stupid question here, but:

I note that the silkscreen on the BoE (serial) shows 6-9VDC.· However, the LM2940C on the board is rated for significantly higher input voltage.· Is there a reason behind the 6-9VDC limitation?

Comments

  • PJAllenPJAllen Banned Posts: 5,065
    edited 2007-03-11 19:16
    Yes, the reason is "heat" (Watts.)··The difference between the input voltage and the output voltage·multiplied by·the current (that is power, watts)·is dissipated across the regulator.· The LM2940 is "rated" for higher input voltage/s, BUT, the current draw (expected) must be de-rated (PD -- total package dissipation) accordingly.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2007-03-11 20:31
    The main reason is that, while the LM2940 can handle more voltage (26V) the VIN also feeds the BASIC Stamp regulator (depending on BOE revision) which cannot handle more than ~12V.·· On the BOE you won't get the full rating for current from the LM2940 without putting a larger heat sink on it.· Take care.

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    Chris Savage
    Parallax Tech Support
  • ForrestForrest Posts: 1,341
    edited 2007-03-11 21:49
    Also note than an unregulated 9V AC/DC power supply will typically output around 13 volts under a light load.
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