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It's me again, still reading AoE 3rd. On page 40, footnote 35, the author writes:

Resonant charging is used for the high-voltage supply in flashlamps and stroboscopes, with the advantages of (a) ......, and (b) no current immediately after discharge (see waveforms), thus permitting the flashlamp to “quench” after each flash.

The waveform looks like this:

enter image description here

So why can resonant charging produce "no current immediately after discharge" but resistive charging doesn't? And I didn't see a current waveform.

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Discharge takes the capacitor voltage to zero.

What is the current through resistor R immediately after discharge with Vin across it (hint, Ohms Law, Vin/R)

What is the current through inductor L immediately after discharge with Vin across it (hint, dI/dt = Vin/L, which given that IL was zero prior to discharge, is what immediately after the instant of discharge? Further hint - a finite value for dI/dt means it cannot change in an instant)

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  • \$\begingroup\$ Actually, I don't really know what "discharge" means here. Connecting a resistor or flash lamp or even wire directly across the capacitor? \$\endgroup\$
    – nalzok
    Jul 9, 2016 at 10:00
  • \$\begingroup\$ So all of a sudden, the voltage across the capacitor becomes 0. Prior to the discharge, the current through L was 0, so at the instant after discharge, it remains 0. \$\endgroup\$
    – nalzok
    Jul 9, 2016 at 10:10
  • \$\begingroup\$ However, another question: How can the current through R prevent the flashlamp from “quench”ing after each flash? This current should flow through C, and have nothing to do with the load. \$\endgroup\$
    – nalzok
    Jul 9, 2016 at 10:13

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