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protecting board from over voltage

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amin5659

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hi all.
i have an analog signal which i want to sample and send to PC with a micro controller or some thing else.
the analog signal comes from out side the board and user can be connect the input to any thing.
i want to protect the pc and the board from risky circumstances like:
over voltage like 220 volt ac and inverse connection and ...
the BW is about 50 mhz and maximum acceptable voltage around 50V. just like an oscilloscope.
can you help me with this?:oops:
 

Are you trying to measure the input voltage with an ADC on the micro controller? What MCU (if you are using integrated ADC) or an ADC IC you are planning to use? Having the specs for the parts you are working with helps to design what kind of a voltage protection circuit you want to put in.

The fact that you might be seeing 220 VAC means that you are not going to want to put anything directly into your ADC from the input. If I were designing a voltage measurement circuit, I would probably use some sort of a differential op amps circuit first before using the ADC to get the mesurement to the MCU with a reasonable voltage range.

hi all.
i have an analog signal which i want to sample and send to PC with a micro controller or some thing else.
the analog signal comes from out side the board and user can be connect the input to any thing.
i want to protect the pc and the board from risky circumstances like:
over voltage like 220 volt ac and inverse connection and ...
the BW is about 50 mhz and maximum acceptable voltage around 50V. just like an oscilloscope.
can you help me with this?:oops:
 

hi thanks.
I'm using ADC08200 200MSample 8bit adc.
this application is quite similar to oscilloscope(analog circuit i mean) which i have to scale the input voltage with some scale factor(like volt division in oscilloscope's)
and as i said before i have to protect the board from over voltage too.
any idea?
 

Hi,

What microcontroller can handle the 200MSample/s?

Overvoltage protection is difficult because:
* protection against overvoltage needs to limit power dissipation --> limit current --> high impedance
* but processing high frequency signals needs low impedance

I have no other idea than a good manual that helps to avoid that a user connects 220V to the signal input.

Klaus
 

thanks for reply.
Actually i am using fpga(spartan3) for this project just said mcu for example.
* protection against over voltage needs to limit power dissipation --> limit current --> high impedance
of course. i want to have 900kohm input resistance.
but processing high frequency signals needs low impedance
i have to design wide band amplifier or wide band voltage scaler(0 to 50mhz)
I have no other idea than a good manual that helps to avoid that a user connects 220V to the signal input.
the circuit i am looking for is very similar to input stage of digital oscilloscope with 200mhz sampling rate and 50 mhz bandwidth with some input protection and this should be achievable. don't you think?!
 

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