Base Drive Is a Current Contract

Base Resistor Sets Base Current

Base drive is computed from the stated input, drop, and resistor. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Only the voltage above the base-emitter drop drives the base

The training input is 5 V and the stated drop is 1 V, so the resistor gets 4 V.

5 V−1 V=4 V5\ \text{V} - 1\ \text{V}=4\ \text{V}
Base-drive voltageInput, drop, and base-current bars are checked.input 5 Vdrop 1 Vbase 1 A

The base current is the resistor voltage divided by resistance

That 4 V across 4 ohm gives 1 A of base drive.

IB=4 V4 Ω=1 AI_B={4\ \text{V}\over 4\ \Omega}=1\ \text{A}
Base currentThe visible base-current vector is exactly one ampere.input 5 Vdrop 1 Vbase 1 A