NCL37733 LED Drivers onsemi NCL37733 LED Drivers are for power-factor corrected flyback and non-isolated buck-boost and SEPIC converters. The controller operates in a quasi-resonant mode to provide optimal efficiency. It embeds a proprietary control method that allows the LED current to be tightly regulated from the primary side. This eliminates the need for a secondary-side feedback circuitry and for an optocoupler.