Electronics 1 — Filters & Op-Amps

Sizing a real part: the LED resistor

continues from lesson 3 — values defined earlier in the course stay live here

Every LED needs a resistor or it dies — the resistor absorbs the difference between supply and the LED's fixed ~2 V drop, at a current you choose:

V_{cc} := 5 V

= 5 V supply

V_{led} := 2 V

= 2 V red LED forward drop

I_{led} := 15e-3 A

= 0.015 A bright but safe

R_{led} = \frac{V_{cc} - V_{led}}{I_{led}}

= 200 ohm = 200 Ω — use the next standard value up

✓ pass

(V_{cc} - V_{led}) * I_{led} < 0.25 W

a quarter-watt resistor survives

Where next: AC Motors — and then Power Systems, where these signal-level ideas scale up to kilovolts.