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DC-10MHz isolation design

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NiHaoMike:
Has anyone designed an isolation circuit for measuring switching power supplies using an oscilloscope? The frequency range is DC-10MHz or so and the isolation needs to be at least 400-600V CAT II.

I have thought about amplitude modulating a 100MHz or so (or optical) carrier, sending it through a transformer, and then synchronous rectifying that to get back the original signal. But that would require careful RF design to work properly.

Another idea is to use a transformer to couple the high frequencies and a some other isolation method to couple the DC and low frequencies, but would that require careful adjustments to ensure a flat frequency response? (Curves are for models, not linear isolation circuits!)

scrat:
The other big problem I see is measuring such a high voltage signal (= using high impedance) up to that frequency, since, for example, at 10MHz cutting frequency, 100kohm input resistance means 0.16pF in parallel.

However, maybe I'm saying a stupid thing, but... what about acquiring data on the measure side and transferring it digitally to the other?

NiHaoMike:
Switching power supplies are not going to be affected by a few pF of loading.

Digitizing the data would basically mean building an oscilloscope from scratch, not exactly practical. That would indeed make the isolation part easy.

jahonen:
How about modifying a 2.4 GHz video link to accept your desired signal voltage range? Well, maybe not up to 10 MHz, but might go near.

Regards,
Janne

NiHaoMike:
I'm pretty sure video is AC coupled with automatic zeroing so that wouldn't work.

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