Table of Contents
Capacitors and Bipolar Junction Transistors make for a good timed fading off circuits.
Looking at the diagram.
- Closing the switch: Instantly charges the capacitor and lets a small amount of current flow through the 10k resistor, base, and emitter to ground. That’s enough current to turn the transistor on fully. The LED lights up based on the current set by the 1k resistor.
- Releasing the switch: Lets the capacitor discharge it’s stored charge through the 10k resistor, base, and emitter. The small amount of current it can provide while doing so allows a lot more current to flow from collector to emitter. The LED will stay on fully as long as the base current is high enough, and then it fades it’s way off as base current goes down.
Video:
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