describe
The SG1540 is an integrated circuit designed to efficiently provide start-up PWM control circuits from high voltage DC bus power in switching power supplies. When used, on the primary side, it reduces the startup current to less than 1mA and allows any standard
A PWM control circuit is used as a primary side controller. When used as a secondary side controller for a power supply, it effectively eliminates the need for a heavy 50/60Hz line transformer with its associated low frequency magnetic fields.
The circuit consists of three parts: the microgap comparator/power switch referenced to the 2.5 volt isolation start-up capacitor, its load, a high frequency square wave with a 200mA totem pole output oscillator driving the isolation transformer; and the second bandgap comparator Lock out the crowbar to prevent start or operation in the event of an overvoltage fault.
The SG1540 is specified for operation over the entire military ambient temperature range of -55°C to 125°C. The SG2540 features an industrial grade range of -25°C to 85°C, while the SG3540 is designed for a 0°C commercial grade range of 70°C

Features Available with primary and secondary side PWM controllers Micropower comparators/switches
- Internal 2.5V bandgap reference
-50mA power switch Square wave oscillator
-500Hz to 200kHz operation
- 200mA output from the totem pole
Eliminate bulky, expensive 50/60 Hz transformers Minimize high voltage bleeder current Programmable startup voltage and hysteresis Internal and programmable overvoltage protection circuit latches Available in 8-pin DIP, 10-pin flat pack, 16 High reliability features of wide-lead SOIC package-SG1540
¨ Supplied with MIL-STD-883
¨ LMI level "S" type available for processing