Significance of power design expertise

Power system design has often been considered a bit of a black art and hence frequently delegated to skilled power design engineers. This was fine in larger companies that could afford such dedicated resource and where a more traditional serial design process allowed the final power requirements to be determined once the system design was complete.

This is rarely the case today and increasingly designers need to embrace both the power supply design as well as the overall system design. Not only that but time-to-market pressures mean that these design elements need to run in parallel, requiring a reasonably accurate anticipation of the power budget long before the system design is complete. This is challenging even for experienced hardware engineers let alone someone new to developing a power system.

Adding to the challenge is the need for power supply certification to ensure compliance with national and international regulations, such as UL for safety and FCC and CE regulations for emissions and interference. Here getting the design right first time is even more important because of the delays and added cost that are incurred if a design has to be reworked and re-certified.

So getting the power design right is vital.

For the experienced power designer the ability to tweak all aspects of a power management system is even more important. This can reduce the system's energy consumption and provide a competitive advantage. It can mean longer operating time, lower operating costs or result in a smaller system. The ability to focus on particular areas such as transient response can provide benefits too.

There are many trade-offs throughout the design process, and while it is possible to look at these with a calculator and a bunch of equations, a spreadsheet or even an evaluation board, the biggest challenge is achieving a working design in a timely manner. Evaluation boards are optimised to demonstrate optimum performance under a fixed set of conditions and their performance rarely reflects real-world operating conditions.

Hardware engineers may turn to design tools for help, however, this often requires a range of tools, and switching from one to the other to get a complete picture, all of which can be confusing for novice power designers. It can be particularly difficult with different types of power design. Industrial LED lighting, motion controls, general switch mode power supplies and power trains all have different requirements that a general hardware engineer may not be up to speed with. Selecting the right components, from the MOSFETs to the power drivers and even the resistors, capacitors and inductors can take considerable time and effort.

Under these circumstances, Power Supply WebDesigner, a suite of tools from Fairchild for designing and optimising a power supply design, is touted to save time and effort. Device selection, design, analysis, and simulation takes only minutes because the models, calculations, and iterative steps of power supply design are built into the tools. The Automatic Design option provides all the mainstream settings and produces a full circuit diagram with a single click.

Consider the example of designing a dimmable 240 Vac LED flyback power supply using the Fairchild FL6630 LED driver. Power Supply WebDesigner generates the simulation for the schematic in under three minutes and provides the transient analysis to show what is happening with the waveforms generated by the design. It rapidly produces a workable design, dramatically simplifying the challenge for the designer.

The FL6630 itself is packaged in an 8-pin small outline package (SOP). It is the basis for a single-stage, power factor corrected (PFC), offline LED driver circuit and uses Fairchild's proprietary TRUECURRENT technology to provide constant current control. This allows for the simplified circuit design for LED lighting applications that the design tool generates.