FCC Exam Question: 39E2

Which of the following statements concerning power supply filters is true?

A. A capacitor input has high output voltage, good voltage regulation, low rectifier peak currents and low
B. A capacitor input has low output voltage, poor voltage regulation, high rectifier peak currents and low
C. An Inductive input has poor voltage regulation, low transformer utilization factor, high rectifier peak currents
D. An Inductive input has good voltage regulation, high transformer utilization factor, low rectifier peak currents
Correct Answer: D

Explanation: Inductive (choke) input filters are designed to smooth the current flowing from the rectifier. An inductor resists changes in current, so it draws current over a longer portion of the AC cycle rather than in sharp pulses. Here's why option D is correct: * **Good voltage regulation:** Because the inductor smooths the current, it helps maintain a more constant output voltage despite changes in load current. When the load demands more current, the inductor releases stored energy, preventing a significant voltage drop. * **High transformer utilization factor:** By drawing current for a longer duration and with lower peak values, the transformer's windings are used more efficiently, resulting in a higher utilization factor. * **Low rectifier peak currents:** The smoothed current flow means the rectifier diodes do not have to conduct very high, short-duration peak currents to charge a capacitor. This reduces stress on the rectifiers and transformer. Conversely, capacitor-input filters provide a higher output voltage (closer to the peak AC voltage) but suffer from poor voltage regulation, very high rectifier peak currents (as the capacitor rapidly recharges), and a lower transformer utilization factor.

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Includes Elements 1, 3, 6, 7R, 8, and 9.