Op-Amps and Saturation
The Inverting Mode Op-Amp
Rf
R1
+
V1
+Vs
-Vs
Vo
0V
In theory, the gain of the op-amp is given by Rf ÷ R1. This
equation works well until the output voltage increases too
much. We must remember that the op-amp has a power
supply.
By increasing the input voltage, we find that the output
voltage is limited. The op-amp cannot give out any more
than about 85% of the voltage it is being supplied with
(±15 V). We say that the op-amp saturates.
Voltage Input / V
-2
-1.6
-1.2
-0.8
-0.4
0
0.4
0.8
1.2
1.6
2
Voltage Output / V
13.55
13.56
13.01
8.7
4.43
0
-4.21
-8.09
-12.14
-12.78
-12.82
Satur ation of an Op-am p in the Inve r ting M ode
15
Op-amp is
saturated
The gain equation works
well on this part of the
graph.
10
Voltage Output / volts
5
0
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
-5
-10
-15
V oltage Input / volts
Op-amp is
saturated
2.5
Saturation
• The op-amp will saturate if the input
voltage is increased too much or if the
gain is increased too much.