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RE: Flying Responses

Title: RE: Flying Responses


I'm probably over-reacting here....

As you know, there are many ways to design passive filters, PI, T, etc...
For lowpass we are talking about series L's and shunt C's.
You can choose large L's and small C's, or visa versa.
The real choice will be driven by economics,
where the L's tend to be rather small (nH or uH), and the caps tend to be large (nF or uF)
in the frequency range we are talking about.

For the purposes on the diode discovery using the transformers that has been shown, the output impedance
of the power supply filter is in series with the loop.
So if that output filter has a relatively low impedance below 100 KHz, the diode detection will work.

I maintain that when you design a practical lowpass filter to tame the power supply so that it does not corrupt the data,

it will also work for the diode discovery, since there will be a shunt cap and therefore low output impedance.

Noise below 10 KHz on the output of a DC power supply, is controlled by feedback and output capacitance, not brute force filters.

Noise from 10 KHz to 1 MHz is controlled mostly by output capacitance, along with some series inductance.
This is driven by economics.
It is desirable and quite natural to have a low output impedance from a constant voltage DC power supply.

Yes, you can design a filter so that the diode discovery using transformers does not work, but it will probably be costly.

- Rick

PS: I always agree with you that we need to do lab work to back things up.