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Re: NSLU2 using 7805s and a 12V battery

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  • Phil Reed
    Take a look at the products from Dimension Engineering. They have a number of small, easily integrated switching power supplies you could use.
    Message 1 of 15 , May 6 8:12 AM
      Take a look at the products from Dimension Engineering. They have a
      number of small, easily integrated switching power supplies you could use.

      http://www.dimensionengineering.com/

      (just a happy customer...)

      ...phil

      --- In nslu2-general@yahoogroups.com, efil vasers <efilvasers@...> wrote:
      >
      >
      > I'm trying to run my NSLU2 (with a 1GB flash drive, connected to an
      old wifi
      > router) from a 12 volt SLA rechargeable battery (5Ah) using 7805 voltage
      > regulators.
      > So far, I've tried a few different regulators (rated 1 or 1.5 amps), and
      > when I turn the NSLU2 on, after about 30 seconds, the regulators are
      too hot
      > to touch and soon shut themselves down.
      > I'm not sure what the problem is.
      > Just to try, I connected it with a single 7805 (1 amp), which
      immediately
      > shut itself off.
      >
      > I connected the regulators in parallel with each other to provide up
      to 3
      > amps (more than the NSLU2 power supply), so I figured that I
      wouldn't need
      > heatsinks for them. Am I wrong, or is my NSLU2 just behaving strangely?
      > How many people out there have tried this?
      >
      > (For those wondering, this is for a robotics project for school, and the
      > NSLU2 is running Debian)
      > --
      > View this message in context:
      http://www.nabble.com/NSLU2-using-7805s-and-a-12V-battery-tp17030363p17030363.html
      > Sent from the Nslu2 - General mailing list archive at Nabble.com.
      >
    • oabroad
      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
      Message 2 of 15 , May 6 9:58 PM
        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).
        >
      • tbering2002
        In nslu2-general@yahoogroups.com, efilvasers ... You might want to take a look at www.national.com and use one of their simple switching
        Message 3 of 15 , May 8 7:32 AM
          In nslu2-general@yahoogroups.com, "efilvasers" <efilvasers@
          ...>
          wrote:
          > 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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