kevin.cheung Posted July 11, 2012 Report Share Posted July 11, 2012 I'm currently using a differential op amp to get a high common mode voltage (200Volts+) down to a reasonable range. I've been using the AD629 http://www.analog.com/static/imported-files/data_sheets/AD629.pdfi want to modify this and get a even higher voltage range. What resistance do I need to add in order to get this to at least 400V? If the output is just a simple scaling off, I can compensate it in software. The circuit is also a bit lacking, so in the future I"m looking to upgrade it. The input impedance is too low for my purpose, and I couldn't find another one that fits my accuracy and voltage requirement, so I'm looking to create my own. Below is my plan:i'm going to create a single stage diff amp with voltage divided input and precision op amp. But I need to find the resistance needed to get the voltage divided diff amp circuit working. By that I mean I couldn't find the transfer function. I was using the node equation for calculation, and I couldn't even verify the AD629's circuit of why the one reference is 21.1K, while the other is 20K, while all others are 380K. I know it has to do with balancing the ratio of (380+20)/380, with 21.1K/20K, can someone help me make sense of this? I really really appreciate this.http://cds.linear.com/docs/Datasheet/1052fa.pdfBesides getting some high precision low temp co-efficient resistance, and a good precision op amp. Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted July 12, 2012 Report Share Posted July 12, 2012 Diff amps are still more like opamps. The instrumentation amplifier your designing is going to be inherently poor because the voltage is too high. The problem is that the ouput will be noise. Only a fragment of the signal will remain, but it may be useful. Quote Link to comment Share on other sites More sharing options...
kevin.cheung Posted July 13, 2012 Author Report Share Posted July 13, 2012 I solved the problem. I guess I'm just very rusted on my op-amp math. @Kevin, what's your recommendation? Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted July 13, 2012 Report Share Posted July 13, 2012 I dont' recommend any circuits I know of. If your design is functional, it may be worth developing. There are many electronics products I have no experience with. Quote Link to comment Share on other sites More sharing options...
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