any need for isolated power supply?

**rushnrockt** · 04-25-2005, 05:37 AM

So as usual at 2 in the morning I come up with a weird question. Hopefully this time I will get something out of it

After staring at the carputer power supplies, I am having trouble figuring out if they are isolated or non-isolated. So my question is whether there is any need for a dc-dc converter in a car to have isolation. Thanks for the input.

**neon_eddy** · 04-25-2005, 08:02 AM

like for audio reasons?.. dc-dc is great in that respect because you never can get a 60hz buzz .

just make sureyou have goot grounding all over..

or am I missing it?

**evandude** · 04-25-2005, 08:41 AM

there's no real reason to use an isolated converter. For AC power supplies, it can make sense, because it's safer to not be connected to AC directly. But in a car you WANT all your electronics to be grounded together for various reasons, and it's not like the input voltage of the car electrical system is any more dangerous than the output... if it's just for reducing electrical noise, then there are better methods you can use... mainly designing a GOOD non-isolated DC-DC, and/or adding smoothing caps and inductors in strategic places in your electrical supply as needed.

**rushnrockt** · 04-25-2005, 04:23 PM

Originally Posted by neon_eddy

like for audio reasons?.. dc-dc is great in that respect because you never can get a 60hz buzz .

just make sureyou have goot grounding all over..

or am I missing it?

evandude got the right idea. I was just wondering if there would be any advantage of say an isolated flyback versus buck/boost converter.

**Juliemac** · 04-25-2005, 08:18 PM

Buck/boost typically operates at 100khz. You would need to reach the 10th sub-harmonic of this frequeny to hit 10Khz (your hearing range). At this level the noise problem will be minor. Good filtering on the supply lines will do the job for you.