Rectifier controller from Zetex said to optimise flyback converter design

Called a ‘zero point detector driver’ (ZPDD) since it accurately senses the point at which secondary current reaches zero, the ZXGD3101 ensures that a MOSFET performs the same function of the diode it replaces while significantly improving power supply efficiency. In a 60W notebook adapter for example, the losses are reduced by typically 20%.

Simpler and more robust than competing synchronous controller ICs, the driver needs the support of just three external passive components and produces source and sink currents of up to 2.5A. Since no timing information needs to be transferred from the primary side and no timing components are needed on the secondary side, the ZXGD3101 is very simple to implement.

The ZPDD incorporates a high voltage differential amplifier stage and a high current driver in the compact SM8 package. It monitors MOSFET Drain-Source reverse voltage and when body diode conduction occurs, 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.

The ZXGD3101 zero point detector driver from Zetex Semiconductors is supported by a ‘plug-and-play’ evaluation board enabling fast evaluation in existing power adaptor designs.