Getting crazy with PSpice and real op.amp.

[negromonte1]

I have to measure the BIAS current in a uA741, by using
the following schematic:

http://img316.imageshack.us/my.php?image=opamp14ji.gif

With real instrumentation (function generator, 20 MHz scope...)
all is ok: the switch is initially closed; after some
second it's open, then in output you can see the offset
of sine signal decreasing up to take the falling sine signal
to the saturation (negative) due to integration of
the BIAS current.

Now, I have to repeat the lab with PSpice and I am not able
to reproduce it such as we did it in laboratory: in Probe
I get always a sine 1V/-1V without the "falling" effect...

I was wondering how I can to config PSpice in order to
achieve this result; I tried to chanhe various settings
with no effect. I'm using PSpice Student version.

Thanks in advance

 

[Helmut Sennewald]

I have to measure the BIAS current in a uA741, by using
the following schematic:

http://img316.imageshack.us/my.php?image=opamp14ji.gif

With real instrumentation (function generator, 20 MHz scope...)
all is ok: the switch is initially closed; after some
second it's open, then in output you can see the offset
of sine signal decreasing up to take the falling sine signal
to the saturation (negative) due to integration of
the BIAS current.

Now, I have to repeat the lab with PSpice and I am not able
to reproduce it such as we did it in laboratory: in Probe
I get always a sine 1V/-1V without the "falling" effect...

I was wondering how I can to config PSpice in order to
achieve this result; I tried to chanhe various settings
with no effect. I'm using PSpice Student version.

Thanks in advance

Hello "negromonte1",

Who told you to use a TCLOSE switch?
Use a TOPEN switch and it should work.

I tested it with LTspice and it's running as expected.

Best regards,
Helmut

 

[Pooh Bear]

I have to measure the BIAS current in a uA741, by using
the following schematic:

It's on the data sheet.

Modelling it won't provide any info that the datasheet won't.

Graham