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7357Re: NSLU2 using 7805s and a 12V battery

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  • tbering2002
    May 8, 2008
      In nslu2-general@yahoogroups.com, "efilvasers" <efilvasers@
      > Next time around, I'm definitely going with a switching regulator.

      You might want to take a look at www.national.com and use one of their
      simple switching regulator circuits. Your battery would last longer,
      and digikey can supply almost all the parts you need to build the design.

      National Semiconductor even has a nice tool
      http://www.national.com/appinfo/power/webench.html to automatically
      design your application.

      Additionally, digikey has some pre-made switching regulator modules.
      If you use those, you only need to add capacitors, and thus they are
      more prototype friendly. Some of the DC-DC modules will be even
      easier to connect than your power boosted 7805. Look at the 78HCT205
      or the 78ST305.

      --- In nslu2-general@yahoogroups.com, "oabroad" <oliverb@...> wrote:
      > I just remembered a design trick for boosting a regulator: one
      > circuit I've seen used a PNP power transistor with the base
      > connected to the INPUT of the regulator (with a bypass resistor,
      > probably 22ohms). By putting the junction on the input side the
      > output regulation isn't compromised by Vbe drop.
      > --- In nslu2-general@yahoogroups.com, "efilvasers" <efilvasers@>
      > wrote:
      > >
      > > First off, I'd like to thank you all again for your help.
      > > I should have done a bit more research before jumping head first
      > into
      > > this project.
      > > Next time around, I'm definitely going with a switching regulator.
      > > My quick solution is this:
      > > A 2N3055, bolted to an old CPU heatsink (which still had some
      > thermal
      > > compound on it), with the base connected to a 7805 (with a small
      > heat
      > > sink), collector to the battery, and emitter to the NSLU2 (and
      > other
      > > electronics).
      > > Also, the ground pin of the 7805 is connected to the real ground
      > > through a 1A diode; when I measured the emitter voltage without
      > this,
      > > it read about 4.4 volts, went up to about 5.2 after adding it (runs
      > > about 4.9 with the NSLU2 on).
      > > The 7805 heatsink doesn't even warm up, while the 2N3055 heatsink
      > > warms up after a couple of minutes, but went back down to near room
      > > temperature when I placed an extra 80mm fan next to it.
      > > I'm using the same solution for the 9 volt regulator (both sharing
      > the
      > > same fan).
      > >
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