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Help me with 12V to 48V DC-DC Converter

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laurianus:
Hi

Need help to design a StepUp convertor(or other sollution) with these features:
Vin: LeadAcid batery 12V
Vout: 36 - 48V(unregulated)
IOut: Up to 10A for maxim 400ms

Can i use MC34063 calculator and IC to do this convertor?

Thanks

Bored@Work:

--- Quote from: laurianus on December 05, 2010, 12:50:09 am ---Can i use MC34063 calculator and IC to do this convertor?

--- End quote ---
No, apparently you didn't even care to read the datasheet of the MC34063. And it looks very much that you in general lack the skills to build one.

I recommend to buy one, they are mass products.

Zero999:
Look in  the RS Components, Farnel, Digikey etc. catalogues.

Psi:
Im a bit confused why you only need it for 400ms but...
to get that output you're going to draw around 53A out of your SLA (assuming around 75% efficiency)
So you're gunna need a decent size SLA.

There are many ways to build want you need.
One way you could do it is to build a DC-DC switchmode stepup using a toroid transformer.
You can buy the toroid core and wind it yourself quite easily, and you learn alot from doing so.
Just keep in mind it cant be any type, has to be a core intended for a switchmode powersupply.
(faulty/damaged highpower car amps normally have some toroid cores you can reuse.)

Youll have to play around trying different numbers of turns to work out which is the best.
If using the toroid core from a car amp you can see how many turns they used on the primary.
It will probably be a something like 10 turns with a tap.

Center tap the primary and feed +12V into the tap, then ground each side of the primary through a fet. You can then drive each of the fets through a transistor in a push/pull arrangement from any of the wide range of swtichmode controllers available.  The TL494 controller is one i've used before that maybe suitable.

Centertap the secondary winding and add two high current schottky diodes + a large cap.
(You want to use a center tapped secondary because it means you only need two diodes to create a fullwave rectifier.
Without the centertap you'd need 4 diodes for fullwave and that eats into the efficiency of the design.)

Dont forget to matchup/tune the switching frequency to get the best efficiency from the toroid you're using.
That part is critical if you wind your own transformer, as you dont really know its exact characteristics.
Start at low current and setup multimeters to watch input/output current/voltage and map out the efficiency over a range of switching frequencys. (Dave's video on switchmode design shows this i think)

I've used this method to build a nice voltage stabiliser (10-15V input - 12V 10A output)

I've even managed to drive this kind of circuit from a 555 timer + inverter logic gate to generate the push/pull output.

There are lots of extra features you can add too, like a high side current sensor IC and feed that back into the switching controllers error amplifer so you have a current limit.

If i remember ill post a circuit diagram tomorrow

Zero999:
I agree, the TL494 seems like a better choice because it's push-pull and using a sinlge ended boost topology is not practical for such a high current.

http://datasheetoo.com/search/tl494+push-pull
http://focus.ti.com.cn/cn/lit/an/slva001d/slva001d.pdf
http://www.chipswinner.com/DS/TL494.pdf

There are also other (better ICs you can use:
LM5030
http://www.national.com/ds/LM/LM5030.pdf
http://www.national.com/appinfo/power/files/LM5030_App_Intro.pdf
http://www.national.com/nationaledge/dec03/article.html

LTC3721-1
http://cds.linear.com/docs/Datasheet/37211fs.pdf

If you're still stuck, buy a pre-made unit as mentioned above.

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