The purpose of this application note is to demonstrate the many advantages of using the Supertex LND150N3 in the start-up circuit for switchmode power supplies. Commonly used low voltage bipolar, CMOS and BiCMOS switchmode power supply PWM ICs usually operate from supply voltages of up to 18V.

Read PDF : http://www.supertex.com/pdf/app_notes/AN-D25.pdf