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 1mA 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.

FEATURES
• Useable with primary and secondary side PWM controllers
• Micropower comparator / switch
- Internal 2.5V bandgap reference
- 50mA power switch
• Squarewave oscillator
- 500Hz to 200KHz operation
- 200mA totem pole outputs
• Eliminates bulky, expensive 50/60 Hz transformer
• Minimizes high voltage bleeder current
• Programmable start-up voltage and hysteresis
• Internal and programmable overvoltage crowbar latch
• Available in 8 pin DIP, 10 pin flat pack, and 16 pin widebody SOIC