Page 143 - Op Amps Design, Applications, and Troubleshooting

126 AMPLIFIERS

listed as 12 volts minimum. The load as seen by our op amp is computed by
applying a basic transistor equation, Equation (2.49).

Thus, the maximum available voltage at the output of the op amp will be consid-
ered to be 10 volts. In practice, it will likely be higher.

Determine the Minimum Output Voltage of Hie Op Amp. The lower
limit on op amp output voltage is determined by the V BE value of the transistor.
The worst-case value for the 2N3440A is given as 1.3 volts. Thus, our op amp out-
put voltage can swing as low as 1.3 volts without fear of clipping.

Determine the Required Bias Voltage at the Output. The output of the
op amp should be biased halfway between its two limits (V SAT and V BE). This is
computed as shown using Equation (2.52):

Determine the Maximum AC Swing at the Output. The output of the oj
amp is centered at the bias level and can swing between V SAT and V BE. The RM!
value of output voltage is computed as

For the present circuit, we have

Compute the Required Voltage Gain. The required voltage gain of the
amplifier circuit is determined by applying the basic voltage gain equation, Equa-
tion (2.1).