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minimum power requirements — Parallax Forums

minimum power requirements

qazxsw21000qazxsw21000 Posts: 13
edited 2011-11-20 13:54 in BASIC Stamp
I found this answer a few times, but can't seem to find it now. At least how much voltage is required to power the BS2 module, and what is the maximum?

Comments

  • PublisonPublison Posts: 12,366
    edited 2011-11-20 10:14
    qazxsw21000 wrote: »
    I found this answer a few times, but can't seem to find it now. At least how much voltage is required to power the BS2 module, and what is the maximum?

    It's in the Basic Stamp Manual around page 8

    http://www.parallax.com/Portals/0/Downloads/docs/prod/stamps/web-BSM-v2.2.pdf
  • Mike GreenMike Green Posts: 23,101
    edited 2011-11-20 10:38
    The maximum voltage that can be used for Vin depends partly on the ambient temperature and partly on how much current is needed. There's a built-in 5V regulator on the Stamp module and it has no heatsink other than the module itself (not a very good heatsink). The amount of power that has to be dissipated as heat depends partly on Vin (actually Vin - 5V) and on the total current drawn from the regulator. The amount of current drawn by the Stamp itself is on the order of 3mA for the BS2 to 60mA for the BS2sx. Any current sourced by the Stamp (a HIGH output) or current drawn from Vdd comes from this regulator and adds to the total current drawn. The heat dissipated is (Vin - 5V) * TotalCurrentDrawn. For example, a single red LED attached between an I/O pin and ground with a 330 Ohm series resistor will draw an additional 15mA when on.

    Anyway, when the regulator gets hot enough, it will shut itself down until the temperature drops and this will turn off the Stamp.

    The minimum voltage for Vin is about 6V. You could run the Stamp with a Vin of 5V, maybe even as low as 4.7V, but the regulator isn't regulating at that point, and eventually the Stamp will reset.
  • PublisonPublison Posts: 12,366
    edited 2011-11-20 11:27
    Looking at the table on page 8 and 9, it would seem that 5 volt input would be the minimum, to the casual observer.

    But...looking at the minimum requirements for each chip, they all indicate a minimum of 5.5 volts. Mike indicates 6.0 volts minimum.

    I think the table should be updated to reflect the correct values.

    (Mike has done more real world applications than me, so I would take his word for the 6.0 volt minimum).
  • Mike GreenMike Green Posts: 23,101
    edited 2011-11-20 12:34
    Since you brought it up, look at the datasheet for the LM2936-5.0 regulator which is what is used in the Stamp modules. There are several graphs showing the dropout voltage vs. temperature and output current. It's roughly 0.2V. That means that any input voltage over 5.2V should result in regulation of the output voltage at 5.0V with the dropout voltage getting a bit higher as the output current increases over 40mA and the temperature rises significantly. You could certainly run the Stamp with Vdd regulated with a Vin over 5.5V. On the other hand, if you're using batteries or an unregulated supply rather than an accurate regulated 5.5V supply, the output voltage will sag pretty rapidly, so you should think in terms of a 6V power supply as a minimum.
  • qazxsw21000qazxsw21000 Posts: 13
    edited 2011-11-20 13:54
    The reason for asking the voltage was because I'd be running it from a 6V supply, and didn't know if the minimum was higher than that. OK guys, thanks.
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