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Help with DC 12v-48v step-up converter

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badpacket94501

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Hi All,

Apparently my memory several semesters at Devry 19 years ago hasn't survived the trip...
I am trying to make a small battery pack to support a consumer device which requires 48vdc, with a max draw of 125ma.
I am planning on running 10 2000mah AA NiMh in series to get me 12v. From there I'd like to use the TI783 http://focus.ti.com/docs/prod/productfolder.jhtml?genericPartNumber=TL783 to step up to 48v.

Since I know my Vin, and max current, would anyone be willing to give me some suggestions on the best way to approach this?

Uh oh, don't tell me I screwed up and ordered something that isn't a step-up controller? If thats the case, is there any easy way to get to where I want to go, or should I look at the max668, or another part?

Thanks for your time
 

crust

Member
Well, the ideal DC-DC converter would consume about 500mA at 12V to generate 125mA at 48VDC, since Pin=Pout. However, it is safe to bet that the efficiency of a DC-DC converter (particulary in the boost case) is not going to be better than 90%. I would guess the best you could do with a single part is maybe 80% or so. In any case, the TI part you mentioned is a regulator rather than a converter -- It would not do what you want. The MAX668 is a boost converter designed specifically for going from 12V to 48V at 1A. Its efficiency won't be as good at 125mA, but it would work for your purpose.
 

badpacket94501

New Member
Hmm

Hmm, interesting but it looks a little light on the current availability. How about this one: http://www.linear.com/prod/datasheet.html?datasheet=52 ?

Checked my device, and found it actually draws 380ma @48v max. Since this device can handle 1.25A, I am thinking it should be more than appropriately sized, especially at only $5/piece. With only 3 resistors, 3 caps and 1 choke, I'm thinking I can build this without much problem. But, would this do the job for me? Do I have to worry about things like ripple on the DC out?
 

pebe

Member
Yes, it looks good. You won't have to worry about ripple because you have a large electrolytic on the output and the switching frequency is high.

Good luck.
 
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