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PSUs 101: A Detailed Look Into Power Supplies

Switching Regulator Topologies

A manufacturer can choose between several switching regulator topologies, depending on the peak current that will pass from the main switchers, the desired efficiency levels, the maximum operating voltage across the switchers and the cost. The table below compares several switching regulator topologies. For more information on this, read the Power Supply Cookbook, by Marty Brown.

TopologyPower Range (W)Vin (DC) RangePrimary/Secondary IsolationTypical Efficiency (%)Relative Cost
Resonant Forward0-6060-400Yes871.2
1T forward0-1505-500Yes781.4
Quasi Resonant100-1000+50-1000Yes87-922.8

In many Gold-, almost all Platinum- and definitely all Titanium-rated units, an LLC resonant converter is used. This converter, utilizing a resonant combination of inductors and capacitors, shapes the voltage and current waveforms in the switching FETs, allowing for soft (zero voltage) switching. This, in turn, leads to RFI and EMI reduction and minimized switching losses, so there is a significant efficiency boost. LLC resonant converters also allow higher switching speeds and higher efficiency. Ninety-three to 96 percent efficiency can be achieved even in higher-capacity PSUs.

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Texas Instruments offers a highly informative PDF guide that describes many commonly used topologies.

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