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Low voltage, high current DC/DC converter

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Pax Writer

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Hello experts

I need to either build or buy a compact DC/DC converter which should live up to these criteria:
Input: 8-15V, or if adjustable input is impossible 12V
Output: 8-10V/30A, fast response to current demand from application.
Size: ~20x7x5cm
No fans

Is this utopia?

If you know any retailers who sell something like this, or know of any open source schematics which you have good experiences with don't hesitate to educate me. I'd prefer to pay my way out of this sort of power supply, but if necessary I don't mind piecing it together myself.
Note that high current draws will usually happen in 3-5 second periods with some seconds of interval.

Sorry if this is the wrong place to ask, and thanks for your help in advance.

/Pax
 
I'm a bit confused on your requirements. If the input voltage is 8-10V does that imply the output is also 8-10Volts? When the input goes above 10V then the output is limited to 10V, is that correct?

Back of the Envelope:
Ouput Power : 10V * 30 A = 300 Watts
Efficiency : assume 80%
Input Power : 300 / 0.8 = 375 Watts
Input Voltage : Assume 10 V
Input Current : = 375 / 10 = 37.5 Amps
Peak Inductor Current : 2 * 37.5 A = 75 amps

Inductors that work in this range are large and expensive. First you have to use a large diameter wire to prevent temperature rise in the inductor. Second you have to find a core material that will handle the field produced by that much current without saturating.

The final requirement, fast transient response, can be very challenging for switch mode power supplies. Generally speaking you have to try to run them at higher frequencies which can be difficult with large inductors. In power supplies as in life everything is a compromise.
 
hi pax.

Unless I am missing something, that sounds like it could be solved by using a 12V lead acid battery.:confused:

If you need to drop the 12V to 8/10v two/three 30Amp diodes is series would get the job done.
 
Papa Bravo: I just wanted a DC/DC converter with independently adjustible input and outputs. However, I now have another solution... See below...

Ericgibbs: Lol... I though I found a good answer, but yours is actually better when considering how simple it is.

To clear things up: Sorry for noobing up the forum. I now have two very good solutions for my very simple problem:
1. Eric's go at it - To simply add a few high current diodes in series with the application, which is a good solution because the app doesn't care that the diodes aren't quite linear components.
2. A simple 555-based PWM controlling a MOSFET also in series with the app (yes, its a DC-motor :) ).
I think this thread is officially closed.
Thank you very much for your time and answers :)
 
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