Buffer a high Voltage

Thread Starter

Dave_Muller

Joined Mar 6, 2020
3
Hello,

In my design I need to buffer about 45V-48V and about 30V. For this purpose I want to use two Opamps in Unity Gain Configuration and chose to use 2 ADA4522 (since it has an input range of 0-55V and low a low offset voltage, see attached schematic). In the simulation the buffer circuit worked without a problem, but in reality I get huge offset voltages between the non-inverting and the inverting input of the ADA4522 (e.g. I get 18.834V on the +IN and 19.745V on -IN in the setup in the attached schmatic).
I already asked about this issue in the analog devices forum (Analog Devices Forum) using a slightly different setup. Apparently there is a problem with connecting the ADA4522 to a high source impedance. Since this can not be avoided in my circuit I am looking for a different way to buffer the voltage. I was thinking of using a different Opamp, even though there are less parts available with the required input range. Furthermore I need low voltage offset < 1mV. But before I just pick a new part I wanted to ask if anybody here knows an Opamp that would work in this case and does not have an issue with high input resistance.

I would appreciate your suggestions/comments.

Regards Dave

setup_buffer2.PNG
 

BobTPH

Joined Jun 5, 2013
2,547
Did you try putting a load on the output? Maybe 10K?

The input bias current is listed at less than 50 pA. That should be perfectly okay with your voltage divider

Bob
 

Janis59

Joined Aug 21, 2017
1,231
High Voltage??? You mean 48 KILOVOLTS??
So, You need a Sample&Hold circuit, seems.
May realize with a normal opamp plus voltage booster, or look octopart for altered Vcc opamps.
 
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