RE: Comparing noise from a linear PSU and an isolating USB adapter PSU

shabaz — Thu, 07 Nov 2024 23:45:33 GMT

I got around to a few measurements of the DC-DC converter in this blog: [mention:f7452b0cdf0c4b779caba3855cfb8a7f:f7d226abd59f475c9d224a79e3f0ec07] a couple of months back.

I achieved ballpark 160 uV (I made an RMS measurement so not ideal). Anything past 10 MHz or so is externally coupled noise, not part of the circuit under test.

I attached the output using semi-rigid coax to a spectrum analyzer too (the measurement is in dBm and not a like-for-like comparison without some maths), and with very small RBW, just to confirm that there's indeed nothing in the spectrum there:

From the spectrum visible in the 'scope screenshot, a better LDO would make a significant difference for that project. I used a TLV7401 LDO because it was low-cost.

Hopefully one day I'll try a different LDO with it. But it is not fun winding transformers.

RE: Comparing noise from a linear PSU and an isolating USB adapter PSU

DAB — Thu, 07 Nov 2024 20:46:06 GMT

Very interesting.

I have not used one of these devices, but you clearly need to look carefully at the output.

RE: Comparing noise from a linear PSU and an isolating USB adapter PSU

dougw — Wed, 06 Nov 2024 14:06:17 GMT

Interesting way to add a negative rail.