Electronics > Beginners
Two Questions - SMPS Buck Regulator and Inductor
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Docara:
Hello everyone,

Making 30+ boards for a basic (on/off) daisy chained lighting control system (RS485).

I'm trying to find a very low cost, low part count and very low quiescent current Buck regulator that would be suitable (low ripple) for directly driving an MCU, differential driver and an automotive high side switch without the need for a secondary LDO linear Regulator or problems with noise.

The application is a marine (automotive system) supplied from 12Vdc and the components supply will be 3V with an absolutely maximum calculated load of 250mA so I'm guessing a 500mA to 1A would be a good design value.

Could someone suggest possible candidates.

And secondly, other than the principle of inductance and inductors, I've not had any dealings with using inductors in anger. Other than basic current and voltage values, how do you go about choosing an inductor for, say, a noisy supply line application or similar or when to use a common mode device
.
I'm interested in line transients and supply filtering applications.

Many thanks


JohnnyBerg:
Perhaps you could give a board with a MP1584 a shot. (about $0.25)

For a quick test you could buy a ready build board for a few bucks on Ali or even find a local supplier when you want to have it tomorrow.

There are plenty online conductor calculators, go for low ripple current through the inductor:

http://schmidt-walter-schaltnetzteile.de/smps_e/abw_smps_e.html
Docara:
Thanks for the reply Johnnyberg

I did see MP1584 on our favourite auction site the best board I found was £23 for 30

Jeees Ali is cheap. :o

Further to my question what sort of values would be acceptable for ripple? I knew ripple is an issue which is why I was going to put a linear after it
Siwastaja:
For powering MCU, differential driver (assuming digital communication), and general purpose power switches, any decent switch mode supply will do just fine. I see no requirements for low ripple. Just pick the cheapest, most integrated, most modern part and follow the appnote example circuit and layout.

Input filtration and protection is the hardest part, especially if you need to care about load dumps. It may be easiest to pick a regulator that can handle up to about 100V input.
JohnnyBerg:
I would use the proposed value of the online calculator.

If you worried about noise, a extra LC filter at the output could help. And, of course, low ESR caps.
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