Electronics > Power/Renewable Energy/EV's

source needed for very low ripple isolated DC-DC converters

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--- Quote from: graybeard on May 31, 2023, 09:35:34 pm ---I am working on a fast turn around project in which I need very low noise PCB mounted isolated 3.3V output DC to DC converters.  I need sub mV output ripple.  I can use multiple converters for lower noise.  Multiple converters with output of 200mA-1.1A or a single converter with an output of 650mA to 3.2A.   Based on DRE I choose an input voltage of 24V, but I am not married to that.  I only need 40V maximum of isolation.  Low output noise is my primary concern.

Linear regulators do not do a great job on noise in the 100 KHz to 100s of Mhz that comes out of the converters I have looked at.

I was hoping to buy something off-the-shelf since I have many design challenges and I do not want to spend time designing filters for the converters.  It seems I may have no choice but to devote time to filter design.

I have talked with the technical reps from several companies, but they just tell be I will need to design my own filters and refer me to their application notes.

Do you know of any companies that I should contact?

Thank you

--- End quote ---
Maybe a bit late, but you requirements aren't clear. "sub mV output ripple" measured how? Peak to peak, or RMS? Then you refer to noise from LDOs in the 100kHz-100MHz bands, unclear how that relates to your requirements. Also if it's isolated then your conducted emissions will also have a common mode component, I'm assuming there's some requirement there. And that's not even getting into radiated emissions...

Even with all those requirements described coherently, it's unlikely that COTS products will have specifications which translate directly to your requirements. For example they may state that they pass specific tests for conducted/radiated emissions, but usually don't share anything beyond the pass/fail result.

Some will specify a maximum output ripple voltage (AFAIK there's no standards for output ripple) but I doubt you'll find anything specified at <1mVpp.

Basically there's no avoiding having to do some manual verification on things like this, whether you go fully custom or COTS.

In my experience, clients who want a "low noise" power supply don't actually know what they need, and give vague requirements. My approach is to suggest some requirements which can be verified, with existing standards if possible. Agree on that and put it in the list of deliverables in the contract. Then when you deliver, and they say "it's too noisy!!" you point to the contract and ask which requirement isn't being met.


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