Page 134 - Op Amps Design, Applications, and Troubleshooting

Current Amplifier 117

1. Output current of 10 milliamps (constant)
2. Input current of 500 microamps
3. Load resistance of < 500 ohms
4. Available power supply of ±15 volts
5. 741 op amp used if practical

Compute the Required Current Gain. The required current gain of our cir-
cuit can be computed with the basic current gain equation, Equation (2.1):

Determine the Maximum Value for Jt 2. The maximum value for R 2can be
found by applying a transposed version of the equation we used for computing
the maximum value for R L:

We will select a standard value less than this—for purposes of our design, a 12-
kilohm resistor for R 2. Notice that we use the worst-case value of 12 volts as the
saturation voltage for the op amp.

Compute the Value of R 1. ^ can be computed by applying a transposed ver-
sion of the current gain equation, Equation (2.45).

A } = -2- + 1, or