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A capacitor can keep proving a little Base current to a PNP Bipolar Junction Transistor (BJT) for a short period of time after the signal voltage has been removed. The capacitor voltage quickly drops though, so less and less current flows through the Base.
- Transistor and LED is on fully while switch is closed. The resistor in series with the LED sets the current. Capacitor quickly charges fully.
- Opening the switch makes it so the capacitor has to provide the base current, as the capacitor’s voltage drops, current drops. The collector will only pass about 200 to 300 as much current as the capacitor can provide. As Base current gets closer to 0 amps, the Collector current (and thus the current through the LED) gets closer to 0A even though it remains 200 to 300 times as much as the Base current.
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