Analog Amplifiers

BJT Operating Regions Lab: Cutoff, Active & Saturation

Master all three NPN BJT operating modes interactively by sweeping base current Ib and monitoring Vce and β-gain live.

Speed
A tiny 0.43 mA Base current through RB = 10 kΩ switches ON a 22 mA Collector current driving the Blue LED! Toggle the Base switch to test Cutoff vs. Saturation.
● CH1: CH1
● CH2: CH2

Engineering Theory & Mathematical Model

Cutoff: Ib=0 | Active: Ic=βIb, Vce>0.3V | Saturation: Vce≈0.1V

Digital switches run BJTs strictly in Cutoff or Saturation to minimize transistor heating (P = Vce × Ic ≈ 0), whereas analog amplifiers bias the transistor in the forward Active region where collector current tracks β × Ib linearly.

Interactive Lab Procedure

  1. Open SW_B to verify Cutoff: Ic = 0 A, Vce = 9.00 V, P_transistor = 0 W.
  2. Close SW_B with RB = 10 kΩ to verify hard Saturation: Vce < 0.15 V.
  3. Raise RB to 120 kΩ to place Q1 in the Active region (Vce ≈ 4.5V) and observe LED dimming.

Technical FAQ

What is the core governing formula for BJT Operating Regions Lab: Cutoff, Active & Saturation?

Cutoff: Ib=0 | Active: Ic=βIb, Vce>0.3V | Saturation: Vce≈0.1V — Digital switches run BJTs strictly in Cutoff or Saturation to minimize transistor heating (P = Vce × Ic ≈ 0), whereas analog amplifiers bias the transistor in the forward Active region where collector current tracks β × Ib linearly.

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.

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