Weak Drive Stays Active - Electronic Circuits XI: Transistor Switching and Device Regions Step by Step

A drive limit below load demand creates an active-region output. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Weak base drive gives only three-halves ampere

A base current of 1/2 A with beta 3 gives a drive limit of 3/2 A.

\beta I_B=3\cdot {1\over 2}\ \text{A}={3\over 2}\ \text{A}

Below load demand, the transistor remains active

Because 3/2 A is below the 3 A load demand, the collector current is 3/2 A and the output is 6 V.

I_C={3\over 2}\ \text{A},\quad V_\text{out}=12\ \text{V} - {3\over 2}\cdot 4\ \Omega=6\ \text{V}