Zetex Semiconductors introduces a high voltage MOSFET to handle the requirements of pre-bias supply circuitry. The ZXMNO545G4 is a 450 V enhancement mode N-channel device used in a simple linear regulator to supply PWM ICs at start-up. The MOSFET is disabled when the converter is fully on. To maximize resistance to high voltage creepage, the MOSFET is provided in a 4-pinned SOT223 package. By disconnecting one of the two conventional drain pin positions, the device’s new leadframe design extends inter-pin spacing, which is helpful to designers in complying with UL and CE creepage distance specifications. The transistor delivers impressive power handling capability as a result of its low on resistance (a maximum of 50Ω), supporting continuous drain currents up to 140 mA and pulsed currents of 600 mA. Switching speed is also fast, with turn–on and rise times specified at 7 ns.