Beta Times Base Current Is a Drive Limit - Electronic Circuits XI: Transistor Switching and Device Regions Step by Step

Beta gives a drive limit that must still meet the load demand. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Beta turns base current into a drive limit

With 1 A at the base and beta 3, the drive-limited collector current is 3 A.

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

The load path has its own current demand

The 12 V supply and 4 ohm collector resistor demand 3 A at the ideal low rail.

I_\text{load}={12\ \text{V}\over 4\ \Omega}=3\ \text{A}