Question
In an amplification circuit with AD822 supplied with +15V/-15V, there could be
an operating condition in which the output of the op-amp is saturated to +15V
(Vin is so high that Vin*G>15V). Besides, in this situation, the output could
be connected through a pull-up resistor of about ten kilohms to a voltage
source higher than +15V. How does the op-amp behave in this conditions and what
is the limit of the value of the voltage applied through the 10kOhm resistor to
the output of the op-amp so not to damage the op-amp?
Answer
The output of an op-amp should not go outside its supply rails as it may
destroy the device. If the load resistance is such that the pull-up resistor
current flows in the load and does not cause the terminal to rise above the
op-amp supply then the voltage on the resistor is unimportant. If you wish the
OP to rise above the rail - do not do it!
It would be sensible to use a schottky diode clamp to prevent the output rising
too high by accident.