A few weeks ago, my colleague Robert Taylor announced that the 2014-2015 Power Supply Design Seminar (SEM2100) papers are now available online. Here are the links to the seven new topics:
Robert provided some brief highlights of the first four topics in his previous post. In this post, I’ll discuss the last three topics.
“Control Challenges for Low Power AC/DC Converters,” which I co-wrote with Rich Valley, discusses how modern efficiency standards and programs have transformed the AC/DC flyback controller. Performance standards from governmental agencies like the United States Department of Energy and the European Code of Conduct provide requirements on the “average efficiency” of external power supplies. Average efficiency is calculated by taking the average of the efficiency measured at 25%, 50%, 75% and 100% of the rated output power. Having high efficiency at the maximum load is no longer good enough; today’s controllers must maintain good efficiency at fractional loads in order to meet these standards. We discuss how a “control law” must provide both variable frequency and variable peak current to keep the efficiency high at lighter loads. We also discuss other relevant features of modern controllers, such as minimizing standby power consumption and implementing primary-side regulation.
In “GaN FET-Based CCM Totem-Pole Bridgeless PFC,” Zhong Ye, Alvaro Agular, Yitzhak Bolurian and Brian Daugherty demonstrate the application of gallium nitride (GaN) FETs in a 750W totem-pole bridgeless power-factor-correction (PFC) circuit. The first part of their discussion compares the characteristics of GaN devices to silicon and silicon-carbide devices. GaN’s superior switching characteristics and inherent lack of an intrinsic body diode make it ideally suited for a totem-pole bridgeless PFC application. This topology reduces losses that normally occur in the input bridge rectifier, further improving efficiency. Their paper concludes with experimental results from a 750W PFC converter demonstrating 98.5% efficiency.
There are many papers and tools available describing the large-signal behavior of the two-inductor-one-capacitor (LLC) converter. However, you will be hard-pressed to find tools for analyzing the small-signal behavior of an LLC converter. “LLC Converter Small Signal Modeling” introduces an extremely valuable small-signal modeling tool for the LLC converter. Author Brent McDonald begins with a summary of the LLC converter and its different operating modes. Next, he describes the modeling process using state-space averaging, shows how to verify the model’s accuracy, and provides some examples of how to use the model to predict the behavior of your next LLC design. This modeling tool is now embedded in the Fusion Digital Power™ Designer software tool.
I am so thankful to have the opportunity to be part of this prestigious seminar series, and I am looking forward to many more to come.
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