Page 61 - Op Amps Design, Applications, and Troubleshooting

44 AMPLIFIERS

Since this is a sinusoidal waveform, we could easily convert this to an RMS value
if desired as shown:

In our present case, the RMS value is found as follows:

As long as the input source can supply at least this much current without reducing
its output, the op amp circuit will not load the source.
Maximum Output Voltage Swing. The output voltage of an op amp is lim-
ited by the positive and negative saturation voltages. These can both be approxi-
mated as 2 volts less than the DC supply voltage. Since the DC supply in Figure
2.3 is ±15 volts, the saturation voltages will be +13 volts and -13 volts for the pos-
itive and negative limits, respectively. Thus, the maximum output voltage swing
is computed as follows:

For the circuit in Figure 2.3, the maximum output voltage swing is found as shown:

z; 0(max) = (+V SAT) ~ (-V SAT)
= (+13 V) - (-13 V]
= 26V

Since both DC supplies are equal, the output can swing equally above and below
0. This is the normal condition.
If you desire to be more accurate in the estimation of output saturation volt-
age, you may refer to the manufacture's data sheet in Appendix 1. The manufac-
turer lists minimum and typical output voltage swings for different values of load
resistance.

Slew-Rate Limiting Frequency. It should also be noted that the above maxi-
mum output is only obtainable for frequencies below the point where slew rate
limiting occurs. This frequency can be estimated with the following equation: