Which of the illustrated figures uses an LC...

Which of the illustrated figures uses an LC choke-input filter? See illustration El-0069.

🔍 Key Concepts

• An LC choke-input filter places an inductor (choke, L1) in series with the rectifier output before the main smoothing capacitor. • A capacitor-input filter has a capacitor (C1) connected directly across the rectifier output, with any inductor placed after that capacitor. • Look carefully at the order of components right after D1/D2 in each figure: is it an inductor first, or a capacitor first, or a resistor?

💭 Think About

• In each option, trace the circuit starting at the rectifier diodes’ output node: what is the very first reactive component (L or C) the current encounters? • Which figure shows the choke (L1) carrying the full pulsating DC current before it reaches the main filter capacitor? • Which configurations instead use C1 immediately across the rectifier output, making them capacitor-input or RC filters rather than choke-input filters?

✅ Before You Answer

• Verify which figure has L1 directly in series with the rectifier output and the load, with C1 from that point to ground. • Confirm that figures where C1 is the first component after the diodes are not choke-input filters. • Eliminate any figure that uses a series resistor (R1) as the main element instead of an inductor, since that is an RC filter, not an LC choke-input filter.