DC offset was not in a single supply with 50 Ohm load

[mohichail]

Hi All,

I am using TLV 2781 Op amp. Rin=4.7k, and Rf=47k. When I put DC 1Mega Ohm coupling at output of the opamp,
I got correct DC offset. However, when the output DC coupling is 50 ohm, The DC offset drops by 80%.
I have seen the current at the output increases as the load decreases.

However, According to the theory, DC offset should not be dependent on the load.

How can I make an Opamp which will give me same DC offset for both 50 ohm and 1 mega ohm loading?

Thank you very much.

 

[jiripolivka]

I think the TLV2781 has the load capacity determined by a maximum output current, and it may be too high for a 50-Ohm load.
You can either find an opamp with a larger load current capability, or you can add a two-transistor output buffer stage to handle the 50-Ohm load. I think the 1 MegaOhm is almost no load and should not be a problem but 50 Ohms is a quite heavy load.

 

[mohichail]

Thanks Jiripolivka. I appreciate your response.

 

[keith1200rs]

I think a few other replies have been lost due to https://www.edaboard.com/threads/241676/

If you didn't see them and have any queries, please repost your circuit and concerns.

Keith