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High Voltage, 'High Frequency' Isolated Voltage measurement?

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JPalombini

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isolated voltage measuring circuit

All-

I am trying to find an appropriate circuit to measure a capacitor that gets charged up to 700 V and then discharged. It is not necessary to capture the negative portion of the oscillations on the discharge. I have tried several 'high bandwidth' opto-coupler but they become incredibly non-linear. The maximum frequency is 700 kHz.

Thanks.
 

FvM

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isolated voltage measurement

My first question is, if the measurement actually has to be isolated, or if a good differential probe would be sufficient? Differential probes with e. g. 1 - 2 kV common mode capability and 20 - 100 MHz bandwith are standard tools in power electronics. They are basically high bandwith differential amplifiers with compensated voltage dividers.

True galvanic isolated probes are mostly using optical transmission respectively coupling, either analog baseband, modulated or digital encoded. Linearity of direct analog (baseband) optical transmission can be improved by feedback circuits. e. g. using special analog two channel opto-couplers.
 

JPalombini

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hv ripple measurement

This is to support a monitoring circuit for a SMPS and will be part of an embedded system, so I can't really throw a differential probe into it... I've looked at the HCNR200 but they seem to be limited in bandwidth.
 

Grabauska

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hcnr200 bandwidth

I'm trying to use the following circuit available on Texas Instruments seminar, ( http://focus.ti.com/download/trng/docs/seminar/Topic7MH.pdf page 7-11) with this HCNR200 but the circuit showed in the pdf seems to be incomplete.

the gain with a dc-source is ok, but when some ripple is injected through the circuit, at 100kHz seem to change quickly the phase.

I was suppose to use this circuit as voltage measure for 48V with 200kHz of ripple for a telecom rectifier, but maybe this hcnr200 doesn't have a good bandwidth.

Maybe you can try to use this circuit to measure this capacito voltage.

it is correct, this 700kHz of ripple?
 

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Re: High Voltage, 'High Frequency' Isolated Voltage measurem

With fast IR-LED and photodiodes, several 10 MHz analog bandwith are achievable, but this implies designing special amplifier circuits. I don't know an above MHz analog coupler as a standard product (but it may exist). Regarding the said differential amplifiers used in probes, I just wanted to suggest the technique, not the probe device.
 

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