Engineering Theory & Mathematical Model
Unlike resistive incandescent bulbs, a Light-Emitting Diode follows the exponential Shockley diode equation I = Is(e^(V/nVt) − 1). Above its forward knee (~1.8V–3.1V), tiny voltage increases cause massive current runaway. Connecting an LED directly across a 9V battery forces amps of current through the semiconductor die, destroying the bond wire within milliseconds. A 330 Ω ballast resistor drops the excess ~6.9V safely at ~20 mA.
Interactive Lab Procedure
- Observe the left Green LED glowing steadily at ~20 mA behind its 330 Ω current-limiting resistor.
- Click the open switch ("Click to Test!") above the unprotected Red LED to connect 9V directly and watch it blow out!
- Click the "🔧 Repair Blown" button in the top toolbar, then insert a 330 Ω resistor to fix the right branch!
Technical FAQ
What is the core governing formula for LED Current-Limiting Resistor vs. Thermal Burnout Simulator?
R_limit = (Vs − Vf) / I_LED — Unlike resistive incandescent bulbs, a Light-Emitting Diode follows the exponential Shockley diode equation I = Is(e^(V/nVt) − 1). Above its forward knee (~1.8V–3.1V), tiny voltage increases cause massive current runaway. Connecting an LED directly across a 9V battery forces amps of current through the semiconductor die, destroying the bond wire within milliseconds. A 330 Ω ballast resistor drops the excess ~6.9V safely at ~20 mA.
Can I modify component values and rewire this circuit live?
Yes! The schematic above runs a live MNA SPICE engine. Click any part to adjust parameters, add or delete wires and components, and click Share URL to save your custom topology.