I have a 12VDC/5A from battery. I want to use that battery to supply 3.3VDC / 600 mA of microcontroller. How should I do it?
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Beware of switching-regulator noise. There will be 0.1 volt of switching ripple (such as 2MHz), determined by the load current and the expense of capacitors (larger is better, but more expensive) on output of the SMPS.
There will also be ringing in the 10MHz region, if the supply has to operate in the Discontinous mode.
And there will be (EVIL) ringing at 100MHz, because of parasitic Ls and Cs. If you need CLEAN 3.3 volts, then cascade a Switcher with a Linear regulator; this is shown below.
Use a buck converter with upto 1A rating. It's good to have some margin. There are 2 types to consider. Non synchronous vs synchronous. The synchronous buck converter is more efficient but also slightly more complex. I think non synchronous should be good enough in your case, but you will decide. Check TI, ST microelectronics, etc. They offer many buck regulator chips. If you want help with schematics, feel free to contact me. I'd be glad to help.
Use any buck switching regulator. Do not use a linear voltage regulator as it is not very efficient for converting a 12v input to a 3.3v input.
Switching regulators are available of TI,ST etc. Another alternative is to buy a power module.(From Traco, Minmax)