,Small Iron-core transformer optimization For low standby power,Three samples were studied to get an idea:1 RS Components 3VA 115Vx2 : 6Vx2 (0.25A), P/N 231-8404 2 Nokia type ACP-7H wall plug charger 3 RS component 2.3VA 230V : 6Vx2 (0.19A), P/N 201-8299,Their performance summarized,Notes:Transformer with similar power ratings.Significant difference on standby magnetizing current while having similar Idle power.,Typical Standby waveforms, contribute to difference in standby loss,Sample #1,Sample #2,Sample #3,Now our optimization process,Well-known factor affecting standby power dissipation:Resistivity of material, type of steel. Laminate Thickness. Maximum flux excursion - 1.6T1.8T. Frequency of operation- constant here (50-60Hz). Mass of core material - Around 0.1Kg Core mass typical.,To reduce standby loss: More turns on the primary winding. Reducing flux density at a fixed voltage and frequency. A lower magnetizing current produces a low standby Copper loss. High grade steel.,Side effects: More turns in the same window area means thinner wire. More turns means longer wire length. The net result is second order resistance increase for both primary and secondary windings. Causing higher full-load Copper loss.,Limitations Temperature at full load. In general 1.52W is acceptable for the size of interest. Maximum full-load efficiency, high full-load efficiency cannot co-exist with low standby power.,Lets see how far this can go,Standby Power Dissipation (W) vs Operating Flux Density, Bop(T)Red - Standby Loss Blue - Full Load Loss Brown - Core Loss,A thermal Limited Design Can achieve 0.3W standby Dissipation,Primary Turns 8200 5500 4000 3300 Secondary Turns 108 72 54 43 Pri Wire guage(AWG) 45 43 41 40 SecWire guage(AWG) 28 26 25 24,Typical Design with 0.6W Standby Pwr,Material Price and Performance,Steel Grade Price Iron Loss Typical MaterialUSD 5.0/Kg 2.4W/Kg 1.8T 60Hz Group Arnold Silectron12 mil, Grain Oriented,Kawasaki 35RM210USD 1.0/Kg 4.40W/Kg 1.5T 50Hz Kawasaki 35RM440,BOM, Estimated , Basic Wall-Plug + Rectifier,Low Standby Items Optimized Standard TransformerBobbin 0.08 0.08Steel 0.30 0.15Copper 0.10 0.07Process 0.14 0.100.62 0.40 Plastic + Hardware 0.25 0.25 Rectifier+E-cap 0.06 0.06=0.93 =0.71,