Fast Generation of Planar Transformer Designs

 There is a drive to make almost all of our electronics smaller, including the power supplies and chargers. Often, it is only one individual component that is responsible for stopping further decreases in size, and in the case of power supplies, this component is usually the transformer. Wirewound transformers are bulky, heavy and often have a relatively wide variation in performance between one device and a similar one, which can decrease the efficiency of the final supply. The only real alternative to wirewound transformers is the planar transformer. Planar transformers are around 50% smaller than wirewound transformers as they use flat windings that have more surface area than the round wiring used in wirewound transformers. That flat surface also allows planar transformers to dissipate heat better, which is ideal for smaller, more energy dense designs. The parameters of the planar design can also be more tightly controlled, helping to keep efficiency high. However, there is a drawback to using planar transformers, they tend to be quite a bit more expensive than wirewound ones. This means that they are usually found in more expensive products than low cost items, but that is still quite a large market.

To get the best out of the transformer, it has to be an integral part of the design. Changes in the design around it may affect how the transformer performs, and in some cases, may require a transformer redesign. To tackle this problem, Power Integrations (PI) has launched a new planar magnetics builder in the latest version of the company’s PI Expert design tool. This allows the planar transformer to be designed alongside the rest of the circuit, and the effects of any changes to the design or the full supply to be calculated. That computation is done in real-time as PI Expert engine uses engineering calculations to define components, along with a knowledge library, meaning they are calculated without having to completely “recompile” the circuit before emulation. The tool generates a complete application-specific planar transformer design complete with detailed documentation and Gerber files ready to be sent to the manufacturer.

PI’s director of training, Andy Smith explained the thinking behind the tool by saying, “We want to make the design of custom planar transformers as simple as possible. It is a usually a very complex process that requires an expert in transformer design. Now, the specification is fed directly into the tool, you press a button and then decide to use planar or wirewound technology and the tool takes care of everything automatically, including the wiring layouts and documentation. The transformer will work as intended in the circuit, meaning there is no need for iterations, which can be expensive and time consuming.”

The magnetics designer function in PI Expert provides full planar transformer information including stack specification, vertical and horizontal PCB construction, trace parameters, current density information and layer resistance. The tool automatically incorporates user-specified creepage and clearance distances necessary to meet safety isolation standards. The GUI provides vertical and horizontal stack construction and a bird’s eye view for all layers.

The tool also contains a comprehensive database of planar cores and components to simplify design and can also accept custom core geometries. PI Expert automatically optimizes the planar transformer design to match the power supply specification, incorporating additional winding layers and adjusting trace geometries when required.

The latest version of PI Expert now also includes support for Power Integrations’ entire InnoSwitch3 flyback switcher IC family.

www.power.com