Ferrite Transformers1 min read
Bay note 08 — Isolation and creepage on purpose
Functional vs reinforced is a winding architecture, not a sticker. How tape, margins and bobbin choice change when the barrier is mains-referenced.
Electrical turns can be perfect and the part still wrong if the barrier is wrong. Isolation is a construction sequence.
Three words that change the build
| Class | What it means on the bobbin |
|---|---|
| Functional | Circuit needs it; not a safety barrier |
| Basic | One level of protection |
| Reinforced / double | Mains-to-SELV style barrier — tape, margins, often triple-insulated wire |
Construction levers
- Creepage distance on the bobbin and between pin groups
- Tape schedule between pri/sec (layers, overlap, margin tape)
- Triple-insulated wire vs conventional + barrier tape
- Slot / bank winding to keep pri and sec apart
What we cannot infer
Vin and Vout never tell us reinforced vs functional. A 400 V boost for a DC bus and a 230 Vac flyback to 12 V SELV are different animals with similar turns math.
What to put on the print
- Isolation class and standard (for example IEC 62368-1)
- Working voltage and overvoltage category if known
- Required hipot test (for example 3 kVac / 1 min)
- Pinout with pri/sec sides labelled
If you are unsure, write "mains-referenced primary, SELV secondary" in plain language — we will translate it into a tape schedule.