MOSFET Tackles Rigors of Power Supply Start-up

A high voltage MOSFET from Zetex Semiconductors has been introduced to handle the requirements of pre-bias supply circuitry. A 450V enhancement mode N-channel device, the ZXMN0545G4 is used in a simple linear regulator to supply power to pulse width modulator ICs at start-up, and is disabled once the converter is fully on.

Compared to alternative resistor dependent solutions, the MOSFET based approach improves system efficiency and reduces start-up time. To maximize resistance to high voltage creepage, the MOSFET is provided in a unique 4-pinned SOT223-package.

By simply disconnecting one of the two conventional drain pin positions, the device's new lead frame design significantly extends inter-pin spacing, which helps designers comply with UL and CE creepage distance specifications.

Characterized by low on resistance (50Ω maximum) and supporting continuous drain currents up to 140mA, and pulsed currents of 600mA, the transistor offers an efficient power handling capability. Switching speed is also fast, with turn-on and rise times specified at 7ns.

The price of the ZXMN0545G4 is 0.32 USD in quantities of 10,000.