NJM4151
III. Design a single supply FVC to operate with a supply voltage of 8V and full scale input frequency f0 = 83.3Hz. The
output voltage must reach at least 0.63 of its final value in 200msec. Determine the output ripple.
1. Set RS = 14.0kΩ
2. T = 0.75 (1/83.3) = 9msec Let R0 = 82kΩ and C0 = 0.1µF
3. Since this FVC must operate from 8.0V, we shall make the full scale output voltage at pin 6 equal to 5.0V.
4. RB = 5V/100µA = 50kΩ
5. Output response time constant is tR < 20msec Therefore CB < tR / RB = 200 x 10-3 / 50 x 103 = 4µF Worst case
ripple voltage is: VR = 9mSx135µA / 4µF = 304mV
IV. Design an opto-isolated VFC with high linearity which accepts a full scale input voltage of +10V. See Figure 7 for the
final design. This circuit uses the precision mode VFC configuration for maximum linearity. The NJM3403A quad
op-amp provides the functions of inverter, integrator, regulator, and LED driver.
Figure 7. Opto-Isolated VFC
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Ver.2003-12-09