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BJT Operating Regions

Defines the three operational states of a Bipolar Junction Transistor (BJT): Cutoff (no current), Active (amplification), and Saturation (low resistance). Operation depends on biasing voltages.

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The statement of the theorem

Let

I_C

be the collector current,

V_{BE}

the base-emitter voltage, and

V_{CB}

the collector-base voltage. The operational regions are defined by the biasing conditions:\n1. **Cutoff:**

V_{BE} < V_{bi}

and

V_{CB} < 0

, resulting in

I_C \to 0

.\n2. **Active:**

V_{BE} > V_{bi}

and

V_{CB} > 0

, where

I_C \neq 0

and

I_C

is governed by the transconductance model.\n3. **Saturation:**

V_{CB} < V_{CE(sat)}

, resulting in

I_C

being limited by the external load resistance

R_L