Electronics > Projects, Designs, and Technical Stuff

DC/DC Converter Noise Troubles

(1/3) > >>

MosFett:
I'm building a battery powered audio amplifier which uses a DC/DC converter to generate a negative rail. My problem is that the converter I designed generates way too much interference in the rest of the circuit. I've spent a few days trying to figure out how to reduce the interference but with no luck. As you can see in the screenshot below, there is a lot of high frequency (about 50MHz) noise present when the converter's inductor (L1) is being charged. I see this noise show up in the rest of my circuit and could even pick it up in an oscilloscope probe (shown in the scope screenshot). Could anyone give me some pointers on how to reduce this interference?

The scope screenshot shows the negative rail (ie. converter output) on CH3 (Pink) and EMI I picked up using a scope probe clipped to its ground cable and circling L2 in CH1 (Yellow).

palpurul:
Something like this happened to me a while ago. I designed a low noise differential amplifier powered by switching converters (+/-15V). I was getting a lot of switching harmonics at the output. No matter how heavily I filtered the output of the switching converters I was getting the same harmonics with almost same amplitude.

I ended up designing the power board seperately and piggybacked the amplifier board and power board with their bottom ground planes facing each other. That fixed my problem.

Desinginig two boards seperately is probably overkill (depending on your requirements ofc), but it worked for me.

Is that a PCB or are you breadboarding?



T3sl4co1l:
Is it actually ~50MHz and not just pulses -- wavelets, ringing?  If so, I'm not even mad, I'm impressed.

Tim

thinkfat:
It looks like you're hitting some resonance at 50MHz which the switching pulse of the converter excites. How did you decouple the converter from the rest of the board? Do you have a single ground plane for the whole system? Maybe if you isolate the switching ground from the rest of the system it gets better. Just tie them together at a single point, maybe you could try to couple the grounds by an inductor.

Does the interference pattern change if you actually put load on the negative rail?

Also, looking at your schematics - you have some pretty large capacitors there, 220µF and 100µF, what type do you use there? They look quite large for ceramic caps and your schematic shows them as non-polar. But if you do actually use electrolytic caps, be reminded that they have quite a huge inductive component in their ESR and also there's self-resonance. Electrolytic capacitors are good for maybe up to 1MHz or so and for higher frequencies they're sort of acting like an inductor.

MagicSmoker:
Personally, I'd try a light RC damper (say, 100p + 10R) across the 1N5819 Schottky or replace it with a fast conventional PN diode. This is because the '33063 is no where near fast enough to excite a 50MHz resonance, but the Schottky is.



Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod