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Old 10th February 2009, 08:37 PM   #1
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Join Date: Aug 2006
Default DC-DC Cuk converter (advice please)

I'm working on a Cuk converter to convert 12v from a computer PSU to 1-14v DC for a peltier thermo-electric cooler. The peltier is about 1.5ohms so the output current will be about 8A and lower. The converter I simulated runs at 50KHz.

Click the image to open in full size.

I'm using the IRF3710 FET, and STPS30100ST Schottky diode (in place of D1).

I plan on using a micro-controller (PIC24) to control the switching frequency but I'm having some trouble converting 3.3v digital logic to the switching mosfet without massive rise/fall times. Is there a chip converter or some design trick to switch the mosfet faster?

Also, the energy coupling capacitor needs a low ESR so I looked at ceramic capacitors but they are very expensive (digikey.ca). I was thinking of using a crossover capacitor such as HERE, but will it be able to handle 50KHz and the massive charge/discharge?

The peltier is going to be used to cool and regulate the temperature in an insulated chamber.

Any other suggestions about the design are also welcome , Thanks.
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Old 11th February 2009, 01:41 PM   #2
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Join Date: Jan 2007
I had a basic circuit that I had designed for driving an LED, so I got back on the LTspice simulator to change it to make it do what you were asking.

I leave the interface to digital up to people with such experience. But one guess would be a digital potentiometer in place of the manual pot.
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Old 11th February 2009, 05:26 PM   #3
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I noticed, just a few posts down, a topic about the IR2110. Looks like it'll do the gate driving in 1 package.
I might step the switching freq up to 100KHz to use smaller inductors.
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Old 11th February 2009, 07:36 PM   #4
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Join Date: Jan 2007
I like the IR2110 a lot. You might consider a high voltage polypropylene or even mylar capacitor in answer to that one question, since the former has one of the lowest ESR values while the latter often works just as well.

But, for what you want to do, I think you might do well with a simpler circuit. That was how I accommodated the request for suggestions. If you like, I can explain how the one I posted works. Or, alternately, if you like, I will redo it on a new thread and we will help you with the cuk way.
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