SG1540 Datasheet | LINFINITY

DESCRIPTION The SG1540 is an integrated circuit designed to efficiently provide start-up power from a high-voltage DC bus to a PWM control circuit in a switching power supply. When used on the primary side, it reduces start-up current to less than 1m A and allows any standard PWM control circuit to be used as a primary-side controller. When used to power a controller on the secondary side, it efficiently eliminates the need for a heavy 50/60Hz line transformer with its associated low frequency magnetic fields. The circuit consists of three sections: a micropower bandgap parator/power switch referenced to 2.5 volts which isolates the start-up capacitor from its load; a high frequency square-wave oscillator with 200m A totem-pole output for driving an isolation transformer; and a second bandgap parator with latching crowbar to protect against overvoltage faults while starting or running. The SG1540 is specified for operation over...