How important is 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 – can save considerable 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.
Using a single stage topology with primary-side regulation, an LED lighting board can be implemented with few external components and minimal cost, as it does not need an input bulk capacitor or feedback circuitry. The tool implements the power factor correction and ensures low total harmonic distortion, with discontinuous conduction mode (DCM) operation.
The constant current approach allows the operating frequency to change by the output voltage to guarantee Discontinuous Conduction Mode (DCM) operation. This provides higher efficiency and simpler design. The device provides protections such as open-LED, short-LED, and over-temperature, and the current-limit level is automatically reduced to minimise output current and protect external components in a short-LED condition.
However, the Auto-Complete feature avoids any of the optimisations that the experienced power designer would add to an implementation. The value of a tool like PowerSupply WebDesigner is not only its ability to quickly generate a design, but also to go back in and optimise the design for a particular set of requirements with the Advanced Step-by-Step Design option.
The bonus for the experienced designer is getting the basics set up quickly which allows more time to focus on the optimisation of the design, tweaking the different elements to boost performance. That combination of tweaking many parts of the system design provides significant benefits, for example gaining a 10% improvement in the transient response to reduce the size of the damping components, so saving cost and reducing power consumption.
Field application engineers (FAEs) at EBV help customers both with the design optimisation and with the component selection and are very experienced with tools such as Power Supply WebDesigner. The support they provide may sometimes involve going back to power component suppliers such as Fairchild. In fact, EBV’s partnerships with suppliers are key to helping designers achieve the best possible implementation in the shortest time. This frees up the customer’s design resources and allows hardware engineers to be more productive throughout the design cycle.
Partners such as Fairchild, whose products cover a wide range of applications, allow FAEs to help the engineer select the right power component for the design, whether it requires a HV IGBT for a high voltage input or AC-DC or DC-DC LED control. With the design tool providing the initial implementation, the FAE can now focus on helping make a real difference to the engineer, with guidance on what kind of topology to use in optimising the number of inductors used in a particular design.
The choice of topology for an implementation can make a dramatic difference to the overall performance and each topology requires a specialised tool. With Power Supply WebDesigner, Fairchild has implemented an easy entry point to select the chosen topology, for example with a PFC buck or a PFC buck boost or flyback for an LED design. This entry panel allows any power designer to easily choose the kind of tool they need.
The same benefits apply to point of load designs that need to be as efficient as possible. Devices such as Fairchild’s FAN23x family are fully supported in the design tools to provide the highest efficiency across the widest range. For point of load applications, the loss analysis is more important to identify the areas of highest efficiency operation, so the tool generates all the performance curves based on the conditions that the designer provides and gives the appropriate power train components along with the full bill of materials with the appropriate temperature specifications.
Such detail allows the engineer to investigate different areas of operation. For example, how does that design compare if the input is changed from 2 A input to 4 A when powering an FPGA, what is the transient response and stability and how does this impact on the overall performance? All of these can be explored in the tool quickly and easily.
Conclusion
The latest power design tools assist hardware engineers whatever their level of expertise. Allowing a novice to quickly deliver an efficient power implementation with a full bill of materials can help to dramatically reduce the stress and strain on the design process. This helps reduce the time to get a wide range of products to market, from industrial lighting to motor control.
Expert power designers can use the same tools to optimize the initial design and apply their experience and skills to improving performance. The tools even allow designers to use their expertise to explore alternative optimisations for innovative new designs.
The authors
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