Engineering Theory & Mathematical Model
A Bipolar Junction Transistor (BJT) operates as a current-controlled current valve modeled accurately here via the full Ebers-Moll equations. When the Base input switch opens, Ib = 0 and the collector-emitter path is in Cutoff (dark LED, Vce = 9V). Closing the 5V logic switch injects Ib = (5V − 0.7V)/10kΩ ≈ 0.43 mA into the Base, driving Q1 deep into Saturation (Vce_sat < 0.15 V) and illuminating the high-side LED.
Interactive Lab Procedure
- Click switch "Base IN" to toggle Q1 cleanly between Cutoff (LED OFF) and Saturation (LED ON).
- Click transistor Q1 to inspect live Vbe, Vce, Ib, and Ic directly in the right-hand Inspector.
- Increase Base resistor RB from 10 kΩ to 220 kΩ to move Q1 out of saturation into its linear Active region!
Technical FAQ
What is the core governing formula for NPN Transistor Switch & Current Gain (BJT Driver) Simulator?
Ic = β × Ib (Active), Vce(sat) ≈ 0.08 V (Saturation) — A Bipolar Junction Transistor (BJT) operates as a current-controlled current valve modeled accurately here via the full Ebers-Moll equations. When the Base input switch opens, Ib = 0 and the collector-emitter path is in Cutoff (dark LED, Vce = 9V). Closing the 5V logic switch injects Ib = (5V − 0.7V)/10kΩ ≈ 0.43 mA into the Base, driving Q1 deep into Saturation (Vce_sat < 0.15 V) and illuminating the high-side LED.
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.