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Boost converter question

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Quank

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Have a happy new year!
I'm building a simple step-up converter with a diode, an inductor, an NMOS and a capacitor. The goal is to convert 4,5 V to 12 V. My question is, the rated voltage of the output capacitor is only necessary to be a little higher of 12 V (ex 16V) or it must be much more? I use a 70 uF capacitor.
Thanks
Quank
 
Provided you have some way of regulating the output to 12V then yes, a 16V cap will just about do. Personally, I'd go for a higher voltage cap, e.g. 25V. The cost difference is insignificant.
 
Make sure you use a Schottky diode as a normal diode will be too slow and you will get a large spike on the drain of the FET.

Take a look at my apps notes (not here to promote my website, but it will explain how boost converters work, starting with the basics)

http://www.simonbramble.co.uk/dc_dc_converter_design/dc_dc_converter_design.htm

You can simulate it in LTSpice:
http://www.simonbramble.co.uk/lt_spice/ltspice_lt_spice.htm

and try different waveforms.

Keep the ESR of the output caps low too to maintain minimum overshoot on the output voltage
 
Have a happy new year!
I'm building a simple step-up converter with a diode, an inductor, an NMOS and a capacitor. The goal is to convert 4,5 V to 12 V. My question is, the rated voltage of the output capacitor is only necessary to be a little higher of 12 V (ex 16V) or it must be much more? I use a 70 uF capacitor.
Thanks
Quank

Hi,

A regular PC power supply uses 16v caps for the 12v lines, and 10v caps for the 5v lines. 25v is better for this hobby stuff though where the voltage might change a little more.
You do have to be a little careful with the ESR in a boost converter which is more sensitive than in other converters. ESR too high means more ripple but a careful analysis of very low ESR shows increased instability when there is a feedback regulation loop.

I have a program that simulates boost converters that allows the selection of various components of the system including feedback compensation networks and output cap ESR values. I can upload it if you are interested in trying it out. Runs on the Windows platform.
 
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