Since the introduction of Switch Mode Power Supplies (SMPS) in the 1960s, the field has seen a series of groundbreaking technologies that have captivated power designers. Among these, magnetic integration in the 70s, soft switching techniques, the rise of MOSFETs, and the advent of digital control were particularly transformative. These innovations didn't just enhance performance—they pushed the boundaries of what was possible, enabling more power to be delivered in smaller, more efficient packages.
From a broader perspective, though, the development of SMPS seemed to plateau after the 1980s. The term "smooth" here doesn’t mean it was dull, but rather that progress became less dramatic. As a result, whenever someone claims they’ve developed a revolutionary power technology, I often find myself thinking, “What’s new under the sun?†It's not that there haven’t been advancements, but the pace has slowed down compared to the rapid evolution of the 70s.
Figure 1: A lot of interesting developments were in the 1970s, and it has been boring until now.
When I began my career as a power designer in 1999, I believed the industry would continue to push toward higher power density. I thought I had the right tools to keep up—increasing switching frequency to shrink transformers and inductors, using soft switching to minimize losses, and relying on better MOSFETs for improved efficiency. That’s how most textbooks described the path forward.
For years, I tried to build a MHz-level isolated power supply, regardless of the application. But one day, an experienced designer shared some research that changed my view: from an efficiency and cost standpoint, 500kHz is the practical limit for commercial isolated power supplies.
This seems to hold true today. For example, components like the LM5025A and UCC2897A can technically operate at 1MHz. They are widely used in telecom DC-DC converters (50–200W), where high power density is key—but I haven’t come across any designs using them above 500kHz.
In AC-DC applications, even the latest analog PFC controllers, such as the UCC28180, are designed to run below 250kHz. Topologies like phase-shifted full-bridge (PSFB) and LLC remain popular due to their soft-switching benefits, yet I haven’t seen many implementations running above 500kHz with controllers like the UCC28950 or UCC25600.
Why is that? The controller isn’t the limiting factor. The real constraint comes from the quality factor (FOM) of the MOSFETs. At MHz frequencies, other challenges also arise, like increased core loss in magnetic components and significant parasitic inductance in capacitors. However, MOSFETs have historically been the main bottleneck.
Over the past decade, a game-changer has emerged: GaN FETs. My team has been working closely with GaN manufacturers to develop gate drivers like the LM5113 and UCC27611. With a much lower FOM than traditional MOSFETs, GaN has reignited my interest in pushing beyond MHz—and even into the 10MHz range.
Driven by the growth of wireless and wireline communication equipment, power density in isolated DC-DC modules reached a new high in 2013, with a one-fourth brick module delivering 864W. By 2014, the industry was already moving toward 1kW. In the next 1–2 years, we can expect MOSFETs, hard switches below MHz, and digital control to play a critical role in this evolution.
I've witnessed the strong desire among isolated power supply designers to break through the MHz barrier. I’m optimistic that within 3–4 years, we’ll start seeing actual MHz products on the market. To make this happen, the industry must fully embrace GaN technology, passive component suppliers need to accelerate their development for MHz operation, and power designers should focus on creating topologies that can handle ultra-high frequencies without sacrificing efficiency. When all these pieces fall into place, the isolated power supply market will undergo a major transformation.
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