Talk to an experienced magnetics design engineer, early in your product design process to discuss the efficiency and cost trade-off’s available for your particular situation.
Looking at your power electronics design requirements and not sure where to start with your magnetics? These 21 Design tips will help to get you started Need more help? Give us a call
Determine ahead of time required electrical standards (e.g. AS/NZ, UL, IEC, CCC, specific industry standards) for your product and its magnetics.
Decide on the required technical characteristics from the transformer in your circuit i.e. inductance, winding capacitance, efficiency, DC resistance, EMI level, etc.
Define any environmental or physical conditions the transformer or product must meet i.e. temperature ranges, humidity levels, vibration resistance, etc.
Choose a standard bobbin & core set to meet your power requirements, while remaining below your temperature rise threshold
Balance the higher cost of SMD magnetic packages with the production efficiencies of pick and place equipment. “Through-hole” components are generally cheaper than SMD, but are more labour intensive to place on the PCB.
As a general rule use a multi-section bobbin for high voltage transformers. This assists with meeting the required creepage and clearance distances.
If temperature rise is not a constaint for your product design, then “push” the transformer by choosing a smaller bobbin and core set to lower cost.
However keep in mind that smaller is not always cheaper. Thin winding wire is more expensive and small transformers can be harder to assemble.
For high frequency transformers, the required ferrite material grade is largely determined by the chosen switching frequency.
Grain oriented (GO) steel is at least 200% more expensive than standard H14 electrical steel, but can only provide up to 30% more power. Going bigger, to get more power is generally more cost effective.
If EMI is not an issue, consider going to higher frequencies to reduce the size of the transformer.
If EMI is an issue, balance the cost of the EMI mitigating choke, with the frequency and size of transformer.
Shielding is expensive. The smaller the transformer, the higher the relative cost impact of adding sheilding.
Typically the inductance values of the core drop significantly, when potted in epoxies. This is due to the risk of cores cracking, causing gaps during the potting process.
MuMetal cores are 4-5 times more expensive than H14 electrical steel. Their price does not justify the improvement in performance. MuMetal cores should be used only to achieve very specific outcomes, not available using other materials or methods.
If efficiency is critical, consider the “skin effect” when selecting your wire size. Use twisted wire or Litz wire to increase efficiency.
Litz wire is extremely expensive and should only be used to provide a specific outcome, not possible by using an alternative. Try twisted wire before going to Litz.
When significant insulation between windings is required, consider using triple insulated wire, instead of standard enamelled wire.
If coupling is critical, consider the “split winding” option.
Always test your magnetics designs in-circuit to insure all critical parameters are met. Assumptions can be costly.