Regarding opamp LM358

[Embedded_Geek]

Hi All,


Is it possible that if I have connected Vcc of opamp to +5V and detect 12V at input, in other words if the input goes beyond the opamp's Vcc. Currently I have done like this but it is behaving ubnormally.


Thanks in advance,

 

[LvW]

Hi All,


Is it possible that if I have connected Vcc of opamp to +5V and detect 12V at input, in other words if the input goes beyond the opamp's Vcc. Currently I have done like this but it is behaving ubnormally.
Thanks in advance,

Does this mean that you are surprised to observe "ubnormal" behavior with a power supply of 5V and an input voltage of 12 V ?

 

[FvM]

I suggest these steps:
- read the datasheet
- design a circuit according to the component specification, e.g. input voltage range

 

[Embedded_Geek]

Does this mean that you are surprised to observe "ubnormal" behavior with a power supply of 5V and an input voltage of 12 V ?

Yeah I am surprised, since it does work perfectly sometimes. Any suggestions?

 

[KerimF]

If we look at the schematic diagram of each LM324 opamp, we see at its input 2 PNP transistors.

Therfore, the difference voltage 7V (12-5) is applied in reverse on two BE junctions.
Even if there is no severe voltage breakdown, the current source (5uA) of the input stage may likely be disturbed in a way which in turn lets the opamp deviate from its normal behavior in some conditions.