Thanks for the detailed explanation. Since i never worked with this type of regulator i was unaware of almost all of it :)
after consideration of your points i decided for a regulator mentionned in a previous post.
I think i found it on mouser: http://www.mouser.lu/ProductDetail/Murata-Power-Solutions/OKI-78SR-33-15-W36-C/?qs=sGAEpiMZZMt6Q9lZSPl3RZClZUSM9XSruU79hDuX5cI%3d
Would this type eliminate all your considerations ?
and i have a few other questions:
what do they mean with voltage nominal ? in this case: "Input Voltage-nominal: 24 V". Are there any considerations when powering such a device from 12v then ?
Which capacitors should be used with such a device ?
just to make sure: this eliminates the need for a linear voltage regulator altogether ?
For your question, yes i power the atmega directly from 3.3 volts and i use it with a 8mhz crystal.
i took the time to do a diagram in eagle (my first) of the circuit as it currently works on my breadboard. Hope that helps.
Note: its a bd137 transistor not a bd139.
They mean that the operational voltage of the regulator suits a 24V system. Such equipments, when operating in DC need to comply with an allowable working voltage spec ranging from 18 to 32V, which the regulator specs meet, BUT not with a 36V nominal system that can typically reach 40+Volts
The graps on Pag 4 show that the max efficiency is archieved at about 300mA+ and show efficiency for different operating voltages., with higher being at 7V and just a bit less at 12V. For peace of mind you can verify that it will deliver the rated 1.5A current, however for protection of your equipment I would use a 500mA resetable fuse just in case something malfunctions (the arduino has one for the USB input, for example).
The device has a built in capacitor and also on pag 4 you can see the ripple as having a max 23mV swing. If this is acceptable (I dont know the requirements of your project/components) just use a general purpose 10V electrolytic storage capacitor and the usual decoupling near the chip. No other special requirements.
If you are using the analog inputs, at 10bit resolution, the usual disclaimer applies for the AVCC supply filtering as with any other power source
Yes, that device eliminates the need for a linear regulator alltoguether, assuming you need a single 3.3V supply rail.