Red Echo

April 30, 2008

I want to drive this motor, which expects 18-24V and draws between 100-400 mA, from a set of four AA cells. I think a PT5049 may be the right solution: minimum input is 4.75 volts, output is 20V, and it can supply up to 0.5A. If I am reading the schematic correctly, the only external components required are a couple of capacitors.

3 Comments

  1. I bet Simon would know all about this stuff.

    Comment by Geoff — April 30, 2008 @ 1:51 pm

  2. Should work. The Integrated Switching Regulator will be less than 85% efficient at 100mA so you will be drawing a bit more current than you think.

    The only place I see the PT5040 in stock is Digikey. They also have the 100uF 50V electrolytic cap which is all that is really needed if the batteries and 100uF are close to the Integrated Switching Regulator.

    search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=PT5049A-ND
    search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=P5571-ND

    They charge $5 for orders under $25 so might want to add some more stuff to your order.

    Using a 6 AA pack might be a considerable improvement in runtime. I use bunches of NiMH cells like these http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=247

    Looks like a cool project.

    Comment by Lewis Gardner — April 30, 2008 @ 9:49 pm

  3. The components will be less than an inch away from the battery pack – this is all going into a little backpack about 5″ square. I think weight is more of a concern than battery life – I only need a charge to last about 6-7 hours. Then again it would be fun to throw some high-intensity LEDs in, so pretty soon we’re up to 300-400 mA, and now we’re just barely lasting 6 hours… okay, yeah, more batteries. 9V is a nice convenient level for LED circuits anyway.

    Comment by mars — May 1, 2008 @ 9:58 pm