Hi All,
I am looking to use a switching regulator as a pre-regulator to power a a battery monitor that will be monitoring a 12 v battery. I have found lots of great information on the forums, which has taken me in the direction of using a switching regulator to reduce wasted power, which is important to me for my application (http://arduino.cc/forum/index.php/topic,108249.0.html, http://arduino.cc/forum/index.php/topic,110954.0.html). So I know that there is a lot of information out there on this subject and I hope I am not being overly repetitive with my post (please point me to anything I may have missed). Alas, I am still a bit puzzled.
A schematic is attached.I have a prototype of this setup working on my bench, sans switching supply.
For my final build, though, I plan to use a Pro Mini board power from the 12v battery using the switching reg, and will be trying to achieve similar precision from the ADC using the 5v reference on the board. So it seems to me quite important to be feeding it (and maintaining) clean power. Also, the final project will be functioning in my camper trailer, and loads on the battery include a DC water pump, fans, and several electric ignitiors for propane appliances...which my reading and instinct tells me are likely to be “noisy”.
From the forums, it sounds like my problems should be solved by adding a fair amount of capacitance at the power supply input, and also spread throughout the circuit. I have tried to do the latter in this schematic to a degree, but I am a bit leery of going beyond the recommended capacitance on either side of the switching regulator, as I am still puzzled by ESR and its relationship to switching regulators/supplies. It sounded simple until I started looking at datasheets. From various datasheets, some switching regs seem to require low ESR at the inputs, some want low at the outputs, many have max load capacitance listed. The part I found recommends a low ESR ceramic across the input, but just a normal old electrolytic at the output, with no mention of ESR. Is this filtering, along with the additional regulation step in the Pro Mini and filtering I have added likely to suffice for me? Any comments or direction to additional information is greatly appreciated!
Mike