AVRFreaks.net

Ross, I'm a strong believer of the principles of the "Darwin Awards" and I've absolutely no desire to reduce the possible errors in a probable design which I have to guess based on little information.

For me there is sometimes a too high level of Hyacinth from "Keeping up appearences" (TV show from the BBC). If you know the show, I like to refer to things like this: http://www.imdb.com/title/tt0098837/quotes?qt=qt1517339

Jan - you seem to confuse galvanic isolation with noise. Galvanic isolation doesn't necessarily isolate you from noise - in fact many fast transients can pass straight through. At DC, the isolation id near perfect but as the frequency rises, the isolation isn't that perfect as there is capacitance between the transformer windings. similarly with optocouplers. Having an isolated converter helps with having voltage drops due to high currents. consider two devices, both powered from the same source but separated by a significant length of wire. Let's say you get 4V of voltage drop across the 0V. With CAN, the 0V reference between the two devices would differ by 4V which might cause a problem. If there was some isolation involved, the voltage drop of the supply voltage would be immaterial and the 0V reference for both devices would be another conductor, but passing very little current in order that they share the same reference.

Further to my mention of the inter-winding capacitance of the dc dc converter transformer, this can couple the switching frequency into both sides of the converter so you need to shunt this with an external capacitor which further degrades any isolation at frequencies above DC.

... and you are entitled to stay silent ... as we all are. But that would make for an awfully quiet forum. Some would say that would be a good thing; I happen to disagree.

My point is: the OP wants to have 24V from batteries converted to 5V, I'm not seeing a question for isolating 2 different designs. Thus I fail to see any reason for isolation or even noise reduction at the battery side. Thus a 'normal' switching regulator would suffice. There are millions of reasons to use or not use DC-DC converters (aka galvanic isolated DC-DC converters) but that is out of the scope of the question from the OP.

Jan,



The OP wanted to know the difference between a 'switching' and dc dc converter. I took that as being the difference between something like a buck or boost design vs a transformer isolated type. I sought to outline the differences. You wanted to know why you would want to use an isolated converter in a battery circuit. For the most part, one would probably use a non-isolated converter in a battery circuit.

My question was answer to the quite patronizing post from mbedder