NPN Transistor
A bipolar junction transistor (BJT) where a small base current controls a much larger collector–emitter current. Used as a switch or amplifier in countless analog and digital circuits.
Properties
| Property | Description | Default | Range |
|---|---|---|---|
| Vce_max | Maximum collector–emitter voltage (V) | 40 V | 5 V – 600 V |
| Ic_max | Maximum continuous collector current (A) | 0.6 A | 1 mA – 100 A |
| hFE | DC current gain — Ic / Ib ratio | 100 | 20 – 1 000 |
| Vbe | Base–emitter forward voltage (V) | 0.7 V | 0.5 V – 0.9 V |
Simulation behavior
The collector current is modeled as Ic = hFE × Ib in the active region. When Vce falls below approximately 0.2 V the transistor enters saturation and current is limited by the external circuit.
Failure occurs if Ic > Ic_max or Vce > Vce_max. The transistor fails open, breaking the collector–emitter path. Excessive base current can also trigger failure if the resulting collector current exceeds the limit.
Tips
- To use the transistor as a switch, drive the base with enough current so that
Ib × hFEexceeds the load current — the transistor then saturates and acts like a closed switch. - Add a 1 kΩ base resistor between the driving signal and the base to limit Ib and protect both the transistor and the driver.
- Increase hFE to model a high-gain transistor (e.g., BC547) and reduce it to model a power transistor where gain is typically lower.