I've posted this elsewhere, so if you've heard it before I apologize. I'm looking for a way to add a USB plug to charge my Iphone, without adding radio interference. The story so far: I've tried a large number of cheap usb adapters, some wired, some install in the lighter socket. All generate some amount of RF, some produce so much noise I can't use the radio. I've done many experiments with this, and I'm fairly certain that the cheap PWM chips pollute the power circuit, turning the entire wiring harness into an RF noise generator. The output seems to be well controlled, and the phone itself is no problem. I've tried various gadgets to filter this noise, including ferrite chokes, diodes, and capacitors. Nothing gets rid of it. So now I'm considering installing an aircraft certified ($$) USB adapter, on the assumption that the FAA wouldn't allow a noisy adapter for aircraft use. The other alternative is to wire up my own adapter using quality chips. I'm attaching a block diagram of what's inside one of these, for anyone interested. And here's the adapater I'm considering:

USB Charger Ports

What I'm wondering is if anyone has actually solved this problem.

Attached Thumbnails

 

Have you tried mounting the power supply in a metal box and grounding the box / tube? ( Faraday cage ) You might be getting noise from radiation not conduction. Have you tried a hand held radio in the car to confirm the noise is coming through the power lines?

Next, the block diagram won't filter noise reflecting back into the 12 V supply only noise moving forward on the 5 VDC line.

How much power do you want to use? You can try a LM7805 regulator chip, these burn off excess power into heat so you will need a decent heat sink. These should make a reasonable clean signal with a capacitor on the output. The LM78xx series can be has in various stock voltages and there are adjustable versions / negative side regulators as well

I've built a Faraday cage, as best as I could considering all the input and output lines. No help. What proved it was that I wired the adapter directly to a 12v battery. If it was propagating over the air, then I would have had the same interference.

The block diagram is an actual adapter. All of the Chinese built adapters I've disassembled have this layout, with no filter at all on the 12V side. LM7805 can't handle enough current. I need 4A to drive two ports.

You could try a LM138 / LM338 , they are adjustable and rated for 5A ( I didn't dig to see if there is a fixed regulator )

http://www.ti.com/lit/ds/symlink/lm338.pdf

I've not got this problem with the thing I use. This might not be relevant but the little clips in the front wheel bearings are designed to reduce interference on your radio. May be checking those would help?

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Easy way is to put extra earth in to each component. From the component to chassis .

Could there be a problem with the radio or radio wiring to make it more susceptible to interference?
Radios have a filter network on each power input. Possibly one of the electrolyic capacitors is defective.
What radio is installed?

It's the stock radio. The Hudson valley is notorious for poor radio reception, and that's part of the problem. I've tried adding an antenna amplifier, but that amplifies both noise and signal, so it doesn't help the noise floor. I have the same problem on my Subaru, BTW. So while it's not out of the question for there to be a problem with the radio, it's not likely.

You might have to go with a linear regulator to get away from the noise as suggested by 97SL320.
Anything with a switching regulator is going to generate noise.
The LM1084 integrated circuit is a fixed 5.0 volt regulator that handles 5 amps with an adequate sized heat sink so you would just need to add a couple of filter capacitors, a TO220 insulator for mounting the IC and possibly a fuse.

I do what rick said, or get your self a CE/UL approved commercial DC/DC converter block. Vicor makes them, and they are sold by Mouser Electronics in Texas or DigiKey in Minnesota. You may find these Vicor's from the parts pullers like AllElectronics or Electronics goldmine..

Another option is the Meanwell makes CE/UL/etc... DC switch mode supplies, and Jameco Electronics in Belmont California sell them, but they sell some pulled parts too. Get on their site or call their tech support..

All the best,

Martin