Maximum output current of a typical flyback power supply is limited by the power loss and heat generated from the output diode when there’s no heatsink. Linear Technology’s LT3809 flyback secondary-side synchronous rectifier driver replaces the output diode forward-voltage drop with the RDS(ON) of an external N-channel MOSFET, thus reducing the power loss and allowing up to 10 A output current without a heatsink. The device senses the MOSFET’s drain-to-source voltage for activation, which eliminates the transformer and allows it to work with the company’s no-opto-coupler products for output-voltage-feedback boundary-conduction-mode (BCM)/critical-conduction-mode (CrCM) flyback converters. Operating input voltage ranges from 4.5 to 40 V, and a 500-µA quiescent current helps maximize light load efficiency. A 1-Ω pull-down gate driver accelerates device turn-off, while low minimum on- and off-times boost noise immunity. Other features include a 22-ns propagation delay, adjustable and accurate trip voltage, and the ability to drive 150-V-rated MOSFETs. The rectifier comes in a 5-lead SOT23 package.