Paul Wagner
Guest
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 Posted:
Fri Mar 25, 2005 10:10 am Post subject:
Re: DC & Op Amps |
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"zero" <slave@discussions.com> schrieb im Newsbeitrag
news:M7P0e.36100$qn2.8080122@twister.nyc.rr.com...
| Quote: | In PSPICE I created a circuit with a VDC = 6V feeding into a uA741 op-amp
in
a inverting amplifier configuration, with both the input and feedback
resistors at 1K.
I expected Vout = -6V but instead got Vout to be about 0V. I also expected
the V- to be 0V because of virtual ground but it came out about 1/2 of
Vin.
I was wondering why the op-amp doesn't amplify at DC.
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It does, but only in the given bounds. For the OPAmp to go to negative
voltages, it has to be supplied with a negative voltage, which means that
you have to use a symmetric power supply (two DC-sources in series, the
connection point being ground).
So use
+6V
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o--------+
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| GND
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-6V
instead of
+6V
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GND
and it will work. By the way, the 741 does reach its supply limits only
within a margin of about 2..3V, so if supplied with +/-6V, you can only
expect +/-4V at the output.
Paul |
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