Electronic Design

Smart Design Squeezes 212-W AC-DC supply Into A 3- By 5-in. Footprint

Any week's e-mail includes new product announcements from power-supply OEMs, but I usually don't write about these releases unless they have something special to say about design. In fact, I'm encouraging companies that send me these announcements to explain how they engineered their products to be smaller, more efficient, more feature-packed, or whatever else might be their claim to fame.

In this case, XP Power's EMA212 incorporates some interesting techniques to squeeze 212-W capability into an ac-dc switcher that measures only 3 by 5 by 1.34 in. (see the figure) The supply was designed for networking equipment, Voice over IP (VoIP) systems, wireless local-area networks, servers, storage-area networks, and post-production broadcast equipment.

Let's see how XP Power achieved that 10.55-W/in.3 power density. The EMA212's two-stage input filter stacks the miniature, high-permeability cores and puts them up into the cooling airflow. Like many OEMs today, XP uses a silicon-carbide (SiC) diode in the power-factor-correction (PFC) circuit. That gains roughly 1% efficiency over a traditional diode and snubber circuit.

Also, the PFC circuit employs a one-cycle control (OCC) circuit, rather than an average current control mode operating over several cycles, eliminating six passive components. A stepped-gap inductor, operating in continuous mode, reduces peak switching current and minimizes filter requirements.

The main converter uses synchronous rectification and a resonant zerocurrentswitching (ZCS) topology. More unusual, a ceramic substrate replaces the conventional heatsink there and on the output rectifiers, saving additional space.

No single technique represents a major breakthrough. But putting them all together to make a supply that will handle better than 200 W and still fit in a three-by-five footprint is solid engineering.

Specs include 90% efficiency at full load, with only 12-CFM airflow required for full-power operation at up to 50°C ambient. (The supply will operate at up to 70°C with de-rating.) Outputs are 12 or 48 V dc, plus a 5-V, 100-mA standby, and 12 V at 1 A for a fan. Signal outputs are ac fail/dc OK, active PFC, remote on/off, and active current sharing.

Sampling now, production quantities of the EMA212 will be available in September. Units cost $82 each in quantities of 1000.

XP Power

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