looking for a good dc-dc step up solution_no real estate..

Discussion in 'The Projects Forum' started by jaydag77, Jan 14, 2008.

  1. jaydag77

    Thread Starter Member

    May 28, 2007
    Hullo again all- today I am again in need of some experience. I have been trying to find a preferably integrated solution that can step up both voltage and current? I am definatly not familiar with building power supplies but have been doing quite a bit of reading about it and also looking at various manufacturer offerings- I am hoping that someone can guide me better than I have been doing!

    I need to step up a N-cell or those rough specs- 1.2vdc @ ?mA to about 3.6vdc @~300mA or better. I also am looking for a better battery choice- should be rechargable and at least as small as an n-cell. If I could find one at 3.3-3.6vdc 300-500mA then I would be in great shape, but haven't been able to find anything that small...

    Am I being unrealistic here? Any advicewould be appreciated, I can provide additional info if needed, but must say that alot of the parts I am using are salvaged, like ir leds so I don't know much about them, which is also causing some headaches....

    The solution I need has to be as small as they get, the pcb itself is only 21 x 19mm and is already packed, I was thinking about making the pow supply a tiny plug-in in series with the batt leads, like a micro dongle or something? I dunno, I just was farting around with the pcb layout late last night and it is increasingly obvious that there are to many parts and not enough space, so I may need to cut back on a couple of functs still...

    thanks in advance--!me
  2. Papabravo


    Feb 24, 2006
    Are you being unrealistic? Yes I think so. In a DC-DC converter with a boost technology you can raise the voltage but the available current is reduced.

    The input power to a converter is volts times amperes with units of watts. Call it Wi. A typical DC-DC converter might be 80% efficient. So the available output power is 0.8 * Wi, call it Wo. Divide Wo by the desired output voltage and what you have left is the available output current.

    So if you need 3.6 V * 300 mA that is 1.08 Watts.
    Input power is 1.08 / 0.80 is 1.35 Watts
    Input Current is 1.35 / 1.2 = 1.125 Amps

    With that kind of current draw your batteries should collapse in the twinking of an eye.
  3. Audioguru

    New Member

    Dec 20, 2007
    My cell phone has a small lithium battery. It is 3.0V to 4.2V (3.6V nominal) and will supply 300mA for 2 hours. It charges in 2 hours.
  4. scubasteve_911

    Senior Member

    Dec 27, 2007
    Power density is definitely one of the most challenging aspects of creating small projects. You should find a small prismatic lithium polymer in roughly the same dimensions as the PCB itself. I believe that they can happily deliver 3.6V@300mA, but you need to be wary of the heat.

    When I was younger and maybe a bit inspired by a recent Mission Impossible film, I tried to make a RF bug device as small as possible. In the end, I had it down to roughly 1cm x 1cm x 2cm. It operated at 900MHz and ran off of a small and expensive prismatic lithium polymer battery. I never built it though, since I didn't know that LTCC circuits cost as much as they did...