“We’ve had PI expert for 25 years and is used by 10,000 engineers. What rapid charging did for low power designs was make transformers interesting,” said Andy Smith, director of training at PI. “Now what we are doing is helping the next part of the miniaturisation. In DC-DC planar transformers have been around for decades but for low power AC-DC chargers they are relatively new.”
“This allows you to reduce the size of the charger, and adapterless charging for wall sockets, that’s where it really works,” he said. “You also increase the surface area of the transformer which is better for cooling.” Transformer Box
The planar magnetics can be designed with coils in a single multilayer printed circuit board or multiple boards for a lower cost implementation. “This means the windings are always predictable without needing a winding machine and things don’t shift, so it’s very consistent manufacturing.”
“But it does have a cost penalty so you have to pick the applications – it’s not insignificant,” said Smith. “For wall sockets, you would perhaps have two outputs with 40 or 50W each. The people making wall sockets with -C and -A are becoming quite common for new wiring, especially in IoT for this kind of technology.”
The PI Expert tool generates a simple, manufacturable design from parameters including the Power Integrations chips that are used, typically with a switching speed up to 140kHz. This design can also be customised.
“What you want to do with the design is consider all the options, the creepage and clearance standards for Europe, the US or China, the altitude operation. . PI Expert already knows the corner cases so the design will work in all possible applications, taking into account the temperature of the windings or variations in the thickness of the copper in the PCB.”
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