Noisy car USB Chargers

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Noisy car USB Chargers

Postby Richie_asg1 » Mon Oct 16, 2017 9:03 pm

Many of us have found out that car phone USB chargers are a source of broadband noise. I have even heard cars drive past and get a swoosh of radio noise when they do.
But as more vehicles have them built-in and hard wired, is the problem going to get worse?

The simple answer is to not use them while listening, but are there quiet ones out there? If not- would it be worthwhile making one? Maybe we can trade efficiency for quiet audio, but I have designed power supplies with enough filtering to remove this noise, and during research on that found a few ic's that incorporate jitter to reduce specific frequency noise.

I have a couple that fit in the cigarette socket that are terrible, so was thinking of a hard-wired alternative that is switched - and quiet.

What are your experiences with them or alternatives?
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Re: Noisy car USB Chargers

Postby Richie_asg1 » Fri Oct 20, 2017 2:19 pm

I've found a LOT of Youtube videos highlighting the problems people are having, from losing all FM radio to freezing MP3 players.

There is also a short thread on Dave's EEVBlog from 2014 - with 2984 views, so it seems there is a problem, and not one good solution mentioned yet.
http://www.eevblog.com/forum/beginners/noisy-usb-car-charger/

Problem seems to be ringing from a very cheap buck converter design that doesn't even use a SMD shielded inductor, uses axial leaded switching diode, and no filter caps at all on the 12v input.

There is a module out there that is called a KIS-3R33S that is a well designed board mount module. It is however configured for 3.3v output but by altering the SMD resistor network in there (or removing it and making your own on a motherboard) you can make it output what you like, and with a bit of extra filtering gets the noise down to 20mV. It also uses a shielded inductor, schottky diodes and most importantly - the whole thing is inside an RF shielded plastic case.

I have used these before in RF PSU's and are fairly quiet by design.
http://www.ebay.co.uk/itm/253190451245

I'm going to buy a USB charger board based on this for £4, Mainly because I don't have any spare USB sockets, and give it a comparative test while using scanner for radiated RFI.
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