Every network transformer datasheet has the same core set of parameters. Here's exactly what each one means and what values to target — formatted for fast lookup.
All key specs in one table
Application OCL Required Pairs Interchangeable?
─────────────────────────────────────────────────────────
10BASE-T 350µH min 2 ✓ with 100BASE-TX
100BASE-TX 350µH min 2 ✓ with 10BASE-T
─────────────────────────────────────────────────────────
1000BASE-T 1000µH min 4 ✗ NOT with above
─────────────────────────────────────────────────────────
WARNING: Do not substitute 10/100 magnetics into a Gigabit design.
OCL is 3× lower than required → degraded link or no link.
DCR and PoE heat dissipation
Power dissipated in transformer winding (Watts)
def winding_power(current_A, dcr_ohms):
return current_A ** 2 * dcr_ohms
Example: 802.3at PoE, 400mA per pair, 3Ω DCR
print(winding_power(0.4, 3.0)) # → 0.48W per winding
Standard transformers are NOT rated for this continuous load.
Always use PoE-rated variants for any PoE application.
Bob Smith termination (all designs)
PHY winding center tap ──[75Ω]──┬──[1000pF]── Chassis GND
RJ45 winding center tap ─────────┘
Omitting this → EMC test failure risk
Sourcing
Voohu Technology (voohuele.com) — network transformers for 10/100 and Gigabit, including PoE-rated variants. Test reports available. 50pcs min, DHL 3–5 days to Japan/Korea/SEA.
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