turns-ratio-scales-voltage - Electronic Circuits XV: Transformers and Coupled Inductors Step by Step

An ideal transformer voltage claim starts with turns and one primary voltage. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

The primary voltage is divided by the turns ratio

The primary side has 12 V. With one shared ideal flux, secondary turns choose the secondary voltage.

V_s=V_p{N_s\over N_p}

More secondary turns gives more secondary voltage

The primary turns and primary voltage stay fixed while secondary turns change.

\begin{array}{c|c|c|c}N_p&N_s&V_p&V_s\\4&1&12\ \text{V}&3\ \text{V}\\4&2&12\ \text{V}&6\ \text{V}\\4&3&12\ \text{V}&9\ \text{V}\\\end{array}

The secondary voltage follows the turns ratio

This is an ideal same-flux voltage ratio. Load current and magnetizing current are not being modeled in this first ledger.

{V_s\over V_p}={N_s\over N_p}=2/4\quad12\ \text{V}\rightarrow6\ \text{V}