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The Old Way

Wed, 10/28/2009 - 8:11am
Power Optimization Welcome to Brainstorm!
To meet the challenge of increased power consumption in today's complex and integrated designs, a variety of techniques are available to be used in combination.


What tools and techniques are available today that help designers to find the optimal power solution very early in the design process?



Environmentally driven design guidelines covering aspects such as power efficiency and standby consumption are coming into force in US, European and Asian markets, and have a major impact on power design in new products. Whether for a mains-powered or battery-operated device, the design of the power conversion architecture holds the key to satisfying these requirements, as well as rules on aspects such as EMC and harmonic distortion.


Determining the optimal power solution early in the design process is vital if the product is to meet all applicable standards and deliver the required performance and functionality, within tight constraints on cost and time to market.

To aid power supply design many vendors of power supply components (e.g. voltage regulators), and complete power supplies provide interactive tools such as online device-selector guides. Such tools allow the engineers to enter key design criteria, such as power rating, input and output voltages, based on which a recommended list of suitable components is generated. Other requirements such as efficiency or transient performance can then be evaluated, to make a final decision. Mechanical aspects such as maximum dimensions must also be considered, to ensure the chosen components or modules will not exceed the form factor of the end product.

More powerful web-based simulation tools provide a virtual workbench allowing designers to configure and evaluate various components and circuit topologies quickly, without committing to hardware. Working from the required design specification and data, a tool such as National Semiconductor's WEBENCH is able to select a suitable power topology and regulator components, help with circuit design, and simulate the behavior of the system. Thermal analysis capabilities also help predict reliability and guide heatsink selection. Manufacturers also regularly update such tools to include their latest products.


The common theme running through all wireless applications is power efficiency. Government regulations on the no-load power and operating efficiency of portable battery-operated equipment chargers are increasingly tough to meet. At the other end of the scale, base stations must be efficient to minimize running costs and avoid unnecessary heat dissipation which can result in larger equipment with unreliable electromechanical elements (e.g., fans).


High-efficiency power supply design is a subtle art with a high premium on practical design experience and requiring time-consuming experimentation. The obvious option is to choose a standard, easily-available power supply from an external vendor, and this approach is favored in many instances. However, an off-the-shelf unit will usually involve some kind of compromise – available power, configuration of outputs, size, and shape – as well as costing considerably more than a simple power circuit BOM and assembly.

The solution is an easy-to-use tool, PI Expert from Power Integrations. More than a simple calculation engine, the software incorporates real-world, practical, electrical design, device selection, and magnetic component optimization experience. It enables engineers skilled in analog and digital design – but perhaps less experienced with power supply development – to create a custom power supply design with a high probability of success.

The software consists of three components:

PI Expert: An interactive program that takes a user's power supply specifications and automatically determines the critical components (including transformer specifications) needed to generate a working switch-mode power supply. Optimization choices for cost or efficiency are included to deliver designs that meet specific needs. The program reduces design time from days to minutes.

PI Xls Designer: A simplified spreadsheet approach to power supply design for advanced users and those who prefer a spreadsheet interface.

PI Viewer: A method for viewing design files created with older versions of PI Expert.

PI Expert Suite is available now for free download at www.powerint.com/pi-expert, with fully supported English and Simplified Chinese versions, as well as a video tutorial to help simplify the process.


Power efficiency is a crucial aspect of wireless power transmission. With diminishing resources and the threatening climate change in mind we cannot longer afford to waste energy, especially for general purpose applications.


Comparing efficiency to a simple cable connection, wireless power will always loose. But compared to a power supply, the result may look different. An additional aspect of saving resources and standby power arises, if one wireless power system replaces several individual supplies. Concluding, comparing a wire with wireless power would be comparing apples with pears.

In an inductive system the magnetic field itself is not lossy. The only losses appear due to the current in the transmitter (Tx) coil, which generates the magnetic field, and in the receiver (Rx) coil, in which a voltage is induced. These losses must be compared to the losses of a transformer in a conventional power supply. Further losses appear in generator and receiver electronics, which are very similar to a switched mode power supply and can be optimized accordingly. Optimizing the losses in Rx and Tx coils however is something specific for an inductive power system.

The coil arrangement is characterized by the coupling factor k between Tx coil and Rx coil and the quality factor Q of the two coils. The losses are proportional to the product Q.k. This means, a bad coupling can be compensated by a better quality factor of the coils or bad coils require a good coupling to get low losses.

Assuming a pretty good quality factor of Q=1000, the efficiency can be calculated for different arrangements by first calculating k. As a rule of thumb, a distance of more than the diameter of the coils leads to an unacceptable low efficiency of a few percent. Consider a small coil to charge a mobile phone and you'll realize that wireless charging in a space like W-LAN is utopistic. However, if the distance is less than about 1/10th of the coil diameter, efficiencies of more than 90% can be achieved. Thus, wireless proximity power at a surface can be an option, which may compete with conventional power supplies.
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The Old Way

Back a few years ago, the typical way to get DC power to a board was to wait until the last minute and get the needed 12V, 5V or other required voltage any way possible. This was accomplished by tweaking a reference design if it was close or delving into the datasheet and running calculations by hand. If the designer got a working power supply, then the problem was solved and forgotten until the next time. But power supply design is not just getting an adequate BOM for something that works. This can lead to a supply that is not the best fit for the user?s needs. Many power IC manufacturers have multiple regulator solutions which might work. Also, there are thousands of different passive component options. How can a designer get the best solution without an encyclopedic knowledge of the products?


The New Way:

Today there are advanced tools from power IC vendors which allow a user to not only get a power supply, but get an optimal solution. The first step for the designer is to define performance requirements such as voltage accuracy, noise and ambient temperature. The designer should next establish the importance of footprint, efficiency and cost, which are three fundamental tradeoffs in design.

Using tools such as National Semiconductor's WEBENCH, the user can then compare 40 or 50 different calculated solutions side-by-side before creating a design. Graphs of efficiency vs. footprint and BOM cost allow the user to weigh the fundamental tradeoffs.

All these designs meet the performance specifications, but it is up to the designer to weigh the tradeoffs and make the best choice based on the design goals of cost, footprint or efficiency. Further analysis can be done at the component level after a design is created.

Once again, all the components meet the specifications and the designer can make the high level decision which best emphasizes the overall thrust of the design. Thus it can be seen that new tools are available to help designers visualize hundreds of different scenarios though graphs and compare the results at a high level. This allows designers an unprecedented ability to get the ideal solution in a very rapid manner.
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