Base Drive Is a Current Contract

Base Resistor Sets Base Current

Base drive is computed from the stated input, drop, and resistor.

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