Alpha and Omega Semiconductor Debuts AC-DC Active Bridge RectifiersApril 07, 2021 by Gary Elinoff
The new family of devices eliminate most power losses in AC/DC power supplies and makes titanium level efficiencies possible
The members of the AlphaZBL family from Alpha And Omega Semiconductor (AOS) serve to eliminate the wasted power inherent in diode bridge rectifiers. By replacing the high forward voltage drop inherent in the Schottky diodes typically employed in bridge rectification, the new units eliminate the wasted energy and the thermal pollution that invariably results.
A typical application for the AOZ7270DI. Image courtesy of the AOZ7270DI Datasheet
The AOZ7270, depicted above in a typical application, is one of the two members of the AlphaZBLTM family. The 600 volt device utilizes an internal 190 mΩ N-channel MOSFET to replace the more typical diode that’s used in AC/DC diode-bridge application. Far less power is lost across the MOSFET than would otherwise be sacrificed to a diode’s forward voltage (VF) drop.
Image courtesy of AOS.
AOZ7270 includes a controller and a 600V MOSFET to replace the schottky diode. Substituting it for the 4 diodes in a full-wave bridge rectifier circuit with AOZ7270s reduces power dissipation and results in improved thermals and higher reliability operation. Most importantly, the controller portion of the device, the part that controls the firing of the internal MOSFET, is self-powered from the AC line. There is no need for a separate voltage supply.
The AOZ7200CI, the second member of the AlphaZBLTM family. It is depicted below, also applied to a bridge circuit.
The AOZ7200. Image courtesy of AOZ7200 datasheet
The difference is that unlike the AOZ7270, there is no internal MOSFET, and the engineer enjoys the freedom to choose a MOSFET that is appropriate to the specific design goal at hand.
The Need for Efficient Power Conversion
As per Colin Huang, Power IC Marketing Manager at Alpha and Omega Semiconductor, “Today’s data centers strive for improved efficiency and thermals as cooling of the data center takes as much if not more power than the servers themselves. AOS’s AlphaZBL products make the design of Titanium grade efficiency power supplies far easier to achieve. He goes on to state that “High power adaptors face thermal challenges in the face of ever-increasing power density. Active bridge rectification enabled by AOZ7200 and AOZ7270 offer the simplest path to reducing power losses.
The AOZ7270, with its internal MOSFET, is designed for applications of 100 watts and above. When compared to a diode bridge in a typical 100W application, the unit provides for efficiency improvements of 0.89% at 115VAC and 0.44% at 230VAC.
Applications for the AlphaZBL devices include:
- Game consoles
- The AOZ7200CI is available in a SOT23-5 package with dimensions (including gull wings) of 2.8 x 2.9 mm
- The AOZ7270 is available in a 5 ×7 mm DFN-12L package
- Both units operate over an ambient temperature range of -40 to +125°C.
Environmental and Safety Concerns
- Both devices are RoHS compliant.
- AOS states that both the AOZ7200CI and the AOZ7270 “exceed lightning surge requirements that are a critical requirement in AC-DC applications.”