Rectifier controller optimises flyback-converter design

Zetex Semiconductors, part of Diodes Inc., has introduced a dedicated rectifier controller that allows MOSFETs to perform as ideal diodes, allowing engineers to eliminate lossy Schottky diodes in flyback converters ranging from 50W to 150W.

The ZXGD3101 controller is a Zero-Point Detector Driver (ZPDD), which accurately senses the point at which secondary current reaches zero. This allows a MOSFET to perform the same function as the diode it replaces, while significantly improving power-supply efficiency. This can reduce losses by around 20% in a 60W notebook adapter. Enabling desk top supplies to achieve operating efficiencies of greater than 78% and no-load power of below 0.5W to comply with forthcoming Energy Star® V2 and European Code of Conduct V3 for external power supplies.

Further benefits of using the ZXGD3101 include reduced power-supply size and weight, as well as simpler overall circuit design. As a less complex and more robust solution than a synchronous controller IC, the driver needs the support of just three external passive components to produce source and sink currents of up to 2.5A. Circuit design is further simplified since no timing information needs to be transferred from the primary side, and no timing components are needed on the secondary side.

The ZXGD3101 incorporates a high-voltage differential amplifier stage and a high-current driver in the compact SM8 package. The ZPDD operating principle monitors MOSFET drain-source reverse voltage. When body-diode conduction occurs, the device produces a positive gate voltage to turn the MOSFET on. Being proportional to the MOSFET drain-source reverse voltage, the drive voltage to the gate is progressively backed off, thereby ensuring rapid MOSFET turn-off at the zero-voltage switching point. This ensures that reverse conduction does not occur.

 

FEATURES Operating modes supported: Discontinuous Mode (DCM) Critical Conduction Mode (CrCM) Continuous Conduction Mode (CCM) 5V to 15V supply-voltage range Reference and bias currents set by external resistors

APPLICATIONS Isolated flyback converters for: Computing equipment Networking devices Test and measurement equipment Embedded controllers

 

 

 

• Freescale Semiconductor’s MSC8113, page 080903
• International Rectifier’s MOSFETs, page 080916

 

Diodes Incorporated / ZXGD3101