Operational Amplifier Applications Unit 6 – Full-Wave Bridge Driver/Conversion
Exercise 2 – Full-Wave rms and Average Converter
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to determine the operating
characteristics of an op amp voltage-to-current converter by applying a sinusoidal input voltage.
You will verify your results by measuring circuit output current.
DISCUSSION
- A sinusoidal input signal is converted into a proportional dc current using a circuit that
consists of a full-wave bridge and an op amp. - The op amp is configured as a noninverting voltage follower. The op amp output is positive
for the positive half-cycle of the input. - The current through the meter always flows in the same direction because the full-wave
bridge rectifier produces a signal with a constant polarity. - R1 is used to establish the relationship of output current to input voltage. Adjusting R1
allows calibration of the meter to read peak-to-peak, average, or rms value of the input sine
wave. - Peak-to-peak voltage (Vpk-pk) of a sine wave is measured between its positive and negative
peaks. - Peak value (Vpk) is measured from 0V to the peak of one half-cycle. The peak value is half
the peak-to-peak value. - The average value (Vavg) of a sine wave is 0V because the portions of the curve above and
below 0V are equal. The meter reads the value of the rectified waveform; therefore the
average value will not be 0V. - The average value of a full-wave rectified sine wave is 63.6% of the peak value.
Vavg = .636 X Vpk - The rms value of a full-wave rectified sine wave is 70.7% of the peak value.
Vrms = .707 X Vpk - Calibration of the meter is determined by adjusting the output current to 1 mA when the input
voltage is set for the appropriate 1V equivalent. For example: set the input voltage to 2.83
Vpk-pk (the equivalent of 1 Vrms), adjust R1 for a 1 mA output and the meter is calibrated to
display Vrms.