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Nead an insulated probe for oscilloscope

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FriedMule:
Thanks I'll read about that system:-)

Just found this US patent: https://patents.google.com/patent/US6603891
Sounds complicated but perhaps something useful?
Is it even possible to build?

capt bullshot:

--- Quote from: FriedMule on June 06, 2019, 04:52:54 am ---What is bothering me is that I may have to pay more then a beginner scope costs:-)
I my naivity, I had hoped for a simpl-ish solution on a circuit, that could isulate my 1x/10x pasive probes for my noob usage.
I thought that a few mega Hertz and voltage under what the scope is build fore, could be handled by some sort of transformer, optocoupler or something like that, could handle it:-)

--- End quote ---

You wrote about measuring the AC input of a bridge rectifier and the output of a 5VDC regulator. One can achieve this with an 4ch beginners scope, using 3 probes. One single ended for the DC part, and the two others for the AC part, scope does subtract these channels.

Otherwise, I'm really often watching more than one signal in a circuit, and have access to various kinds of isolated channels on scopes and differential probes, but rarely need them. Most of the measurements can be done with all scope inputs connected to one common GND in the circuit. Speaking your simple example, I'd connect one channel to the regulators output and the other one to its input to see the rectified ripple - this usually gives you the same information as watching the AC side.

Of course, there are situations where you _need_ an isolated input or a differential probe - e.g. watching gate driver signals on large IGBT modules, or debugging PFC stages and the like. Most small signal measurement can be achieved with your standard single ended probes.

Edit: BTW, the isolation technique used by the A6902 is the same as the THS720 uses - a HF transformer path and a LF optocoupler. The TPS20xx somehow replaced the optocoupler part by transformer and encoding / modulation stuff. Splitting and re-combining the frequency band can be hard to get right. You'd still have to place the step attenuator (say the 10mV 20mV ... 20V / div switch) on the isolated side.

The most modern Cleverscope does it the digital way, placing the ADC on the isolated side. Same did I when I developed rather low frequency isolated input channels for power line transient recording usage in a former job.

David Hess:
The A6902 service manual at that page has a detailed description and full schematic.  It works like you suggested with a parallel path using transformer isolation at high frequencies up to 20 MHz and a linear optocoupler for low frequencies down to DC.  It would not be difficult to duplicate but it would be a lot of work.

capt bullshot:

--- Quote from: FriedMule on June 06, 2019, 05:32:04 am ---Thanks I'll read about that system:-)

Just found this US patent: https://patents.google.com/patent/US6603891
Sounds complicated but perhaps something useful?
Is it even possible to build?

--- End quote ---

Tek did a probe that uses optical fibers only to transfer power, the signal and some control data. I've seen this probe working, it was quite bulky and you wouldn't ask for the price tag ;)
Otherwise quite impressive specs.

FriedMule:

--- Quote from: David Hess on June 06, 2019, 05:39:44 am ---The A6902 service manual at that page has a detailed description and full schematic.  It works like you suggested with a parallel path using transformer isolation at high frequencies up to 20 MHz and a linear optocoupler for low frequencies down to DC.  It would not be difficult to duplicate but it would be a lot of work.

--- End quote ---
Wary interesting!
If we ignore the part of 3000V and instead say maybe 100V, could that not be made with SMD 1206 in a much smaller box with maybe some standard probes attached?
You write "not difficult to duplicate but a lot of work" ehm I am not sure I understand? To me it look like a wary difficult task to duplicate the schematic, since I have about no idea on what does what, so I have to duplicate every line and comma. :-)

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