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OP-AMP,lm2904 and 1458, Both teminal is graunded but output

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kenshin511

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I use 2904 and 1458 op-amp.
Both teminal is graunded
so I think output is zero.
but output exist about 3.9V or 3.6V.
I want to know. why?
 

Re: OP-AMP,lm2904 and 1458, Both teminal is graunded but ou

Recall that the input of the op-amp is a differential pair ..
In practice, the two transistors are not perfectly matched and an offset shows up as a non-zero DC offset at the output ..

Vos * {open loop} gain ..

There is also the [Δ Ibias] issue but when both inputs are connected to the same point this difference plays minor role ..

Rgds,
IanP
 

Re: OP-AMP,lm2904 and 1458, Both teminal is graunded but ou

if the offset voltage is in mv then it may be OK. please cgheck the data sheet for maximum offset limit. if the offset is in V as you have said, you have either wrong pin connections or opamp is BAD.

hock
 

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