Bay note 01 — The print that gets a quote in one exchange
A winding-bay checklist of the eight numbers, plus a worked peak-current strip so the first sample is the right sample.
Every transformer we wind starts as a print — or as a paragraph that wishes it were a print. This note is what the bay needs before copper goes on the bobbin, written the way we actually open an enquiry.
Plate: what must be on the sheet
| Field | Why the bay cannot invent it |
|---|---|
| Topology | Flyback, forward, push-pull, LLC and half-bridge wind in different orders |
| Switching frequency | Sets core loss, material grade and roughly the core size |
| Input voltage range | Vin(min) sets primary turns; Vin(max) sets insulation stress |
| Outputs | Volts and amps per winding, including aux / bias |
| Duty or turns ratio | Send either; we derive the other |
| Lp or Ipk | Energy per cycle — saturation lives here |
| Isolation class | Functional, basic or reinforced, and the standard |
| Envelope | Max L×W×H, pin pitch, THT or SMD |
Worked strip — peak current people forget
A 65 W flyback, Vin 90–265 Vac (about 127–375 Vdc after bridge), Vout 24 V / 2.7 A, fsw 65 kHz, target Dmax 0.45 at Vin(min).
- Power throughput with efficiency η ≈ 0.85:
Pin ≈ Pout / η = 65 / 0.85 ≈ 76.5 W - Average primary current at Vin(min):
Iavg ≈ Pin / Vin(min) = 76.5 / 127 ≈ 0.60 A - For a triangular primary current with ripple factor near 1:
Ipk ≈ 2 × Iavg / Dmax ≈ 2 × 0.60 / 0.45 ≈ 2.7 A - Primary inductance from energy:
½ Lp Ipk² × fsw ≈ Pin→Lp ≈ 2 × Pin / (Ipk² × fsw) ≈ 320 µH
That Ipk ≈ 2.7 A and Lp ≈ 320 µH pair is what we gap the core to. Average current alone under-sizes the gap and the core saturates on the first brown-out test.
What to put on the print
- Topology and fsw
- Vin(min)/Vin(max), Vout/Iout per winding
- Ipk or Lp (or both)
- Isolation: functional / basic / reinforced + standard
- Max envelope and preferred core family if you have one (EE, ETD, PQ, RM)
- Creepage target or mains-referenced barrier note
How we reply
Within one working day you get a design path: core size, material grade, turns sketch and sample lead time — not a ticket number. Send the sheet via contact or a quote request in the app.