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Today’s automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control System Technicians calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. Click this link for more information about the CCST program. ### In a full-wave bridge rectifier circuit used in power supplies, as shown in the post image, which statement below is true?

a) the input current between terminals A and B is a sinusoidal AC current, and the output voltage between terminals X and Y is an inverted AC voltage
b) the output voltage between terminals A and B is an AC voltage, and the input current between terminals X and Y is a square-wave DC current
c) the output voltage between terminals A and B is a constant DC voltage, and the input current between terminals X and Y is a sinusoidal AC current
d) the input current between terminals A and B is a sinusoidal AC current, and the output voltage between terminals X and Y is a constant DC voltage
e) none of the above

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Answers B and C cannot be correct, since Terminals A and B are used for the input current to the transformer circuit. Answer A is not correct since the output from the diode bridge and RC filter circuit is a DC voltage, not an inverted AC voltage. The correct answer is D. The input current between terminals A and B is a sinusoidal AC current, and the output voltage between terminals X and Y is a constant DC voltage. The transformer accepts an AC current. The diode bridge rectifies the sinusoidal waveform of the AC current and produces a DC ripple voltage, but the RC filter circuit smoothes out the voltage pattern to give the constant DC voltage shown in the figure below.

Reference: Thomas A. Hughes; Measurement and Control Basics, 5th Edition, ISA Press. Shares