SMPS Transformer Design¶
Switching Mode Power Supplies user ferrite core transformers and they come in various sizes. Its winding turns are required to be calculated.
Core Size to Output Power Level Recommendation¶
|Output power level (watts)||Recommended core types|
|0–10||EFD15, EF16, EE19, EFD20, EFD25|
|10–20||EE19, EFD20, EF20, EI22, EFD25|
|20–30||EI25, EFD25, EFD30, ETD29, EER28(L)|
|30–50||EI28, EER28(L), ETD29, EFD30, EER35|
|50–70||EER28L, ETD34, EER35, ETD39|
|70–100||ETD34, EER35, ETD39, EER40|
|100–150||EI50, EE40, EER42|
|150–200||EI60, EE50, EE60, EER49|
|200–500||ETD44, ETD49, E55|
|> 500||ETD59, E65, E70, E80|
Calculate Primary Turns¶
For Half Bridge Topology¶
Equation from Tahmid's blog http://tahmidmc.blogspot.com/2013/02/ferrite-transformer-turns-calculation_22.html
- Vin(nom) – Nominal input voltage. For 220VAC it will be VDC
- f – Switching frequency in Hertz.
- Bmax – Maximum flux density in Gauss. Take Bmax in range 1300G to 2000G. Too hight Bmax will cause transformer to saturate and too low will be under utilizing the core.
- Ac – Effective cross-sectional area in cm2. This can be get from datasheets. Ac also referred as Ae. For ETD44, it is 1.75cm2. For EI33, it is 1.19cm2 (from TDK datasheet)
Auxiliary winding calculation¶
Turn ratio for auxiliary
- Naux – Number of turns in auxiliary.
- Nsec – Number of turns in secondary.
- Vaux – Voltage required from auxiliary.
- Vd(aux) – Forward drop in voltage of diode at auxiliary.
- Vsec – Voltage output of secondary.
- Vd(sec) – Forward drop in voltage of diode at secondary.