Boost converters

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strud
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Boost converters

Postby strud » Fri Sep 25, 2020 8:53 am

I have some boards that need to run between 5 & 6V at considerable current (1A near continuous with peaks around 2A) and hence need some form of voltage regulation since no battery options are really suitable.

I plan to put together a design for a boost converter to meet this requirement, but in the meantime I have been using the following units from Pololu running of a single 18650 4000mAh LiIon cell:

https://www.pololu.com/category/145/u3v50x-step-up-voltage-regulators

https://www.pololu.com/product/2565#lightbox-picture0J4880;main-pictures

These have been used for some noise sensitive applications eg telemetry systems etc and worked nicely.

These are being replaced by a newer and 'more betterer' design and I've ordered a number of these to try:

https://www.pololu.com/category/243/u3v70x-step-up-voltage-regulators

https://www.pololu.com/product/2891#lightbox-picture0J9097;main-pictures


Keen to hear of anyone else using boost converters running of single LiPo in similar arrangements.

strud
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Re: Boost converters

Postby strud » Sun Sep 27, 2020 7:44 pm

So knowing that a boost converter running from 1 or more Lithium cells is something I'm going to need going forward, I designed on up using a nice little part from Ti.

Image

Image

Board dimensions are 30mm x 15mm, nothing on the backside. Mounting holes are 2.8mm ie for 2.5mm fasteners.

I have some options for adding extra capacitance if required on the output, depending on the ripple and variance of the load etc.

BOM cost should come in under $5 to $6, compared to about A$20+ for something equivalent eg good for > 4A if needed and having a good heat dissipation design (many of the cheapo boards might have a switcher that is rated for decent current but can only support it for a very short period due to poor heat dissipation)

However, main reason I will make these is so I can tune up voltage etc as required and have them on hand when needed. Getting stuff from overseas now is taking for ever!

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SpaceManMat
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Re: Boost converters

Postby SpaceManMat » Mon Sep 28, 2020 3:11 pm

I take it your not using these for circuits powering igniters? Too likely spike higher currents / short,
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strud
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Re: Boost converters

Postby strud » Mon Sep 28, 2020 5:21 pm

Would not use in circuits that can generate a short, however a 4A rating should enable to run devices that do drive squibs or ignitors if they have current limiting.

The 2nd iteration of the RocTrak board has 1.9A current limited smartfets hence would be happy to power that application.

strud
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Re: Boost converters

Postby strud » Fri Oct 09, 2020 7:46 pm

Did find a nice alternative for mid power (say up to 1A cont) applications on the cheap.

These super cheap boost converters have rather HUGE ripple with almost any load on them :

https://www.aliexpress.com/item/32366166138.html?spm=a2g0s.9042311.0.0.11314c4d5nPJ1F

Image

datasheet of switcher: https://www.olimex.com/Products/Breadboarding/BB-PWR-3608/resources/MT3608.pdf

So when running off 4.2 down to say 3.3V boosted to 5V out with a 0.5A+ load the ripple is at least 200mV ie horrible. The reason being is that there is basically NO capacitance on the output.....(well maybe 1uF)

So I did a little test by putting a 100uF cap across the output and applied the same loading conditions, ripple dropped down to sub 5mV...

Image

So for under $2 you now have a pretty decent adjustable boost converter good for at least 1A continuous, however heat sinking of the little switcher looks pretty ordinary so not sure how long it fare for long runs.. TBD


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