Transformer size is mainly determined by power (VA), not just voltage. Here’s a brief step-by-step guide of sizing a small transformer provided by Partopia Transformer.
Sizing a small transformer (step-by-step):
- Know the input voltage (e.g., 120 V or 230 V AC)
- Know the required output voltage (e.g., 12 V AC, 9 V AC)
- Find the load current – From the circuit or device (in amperes)
- Calculate required power (VA) – VA = Output Voltage × Output Current
- Add a safety margin – Choose a transformer rated 20 – 30% higher VA than calculated
- Check physical & mounting constraints – PCB-mount, encapsulated, open-frame, size limits
Example:
12 V, 1 A load → 12 VA
Add margin → choose 15 VA or 20 VA transformer
