描述 Description

Key Features:· Useable with primary and secondary side PWMcontrollers· 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 crowbarlatch· Available in 8 pin DIP, 10 pin flat pack, and 16 pinwidebody SOICThe 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.The circuit consists of three sections: a micropower bandgap comparator/power switch referenced to 2.5 volts which isolates the start-up capacitor from its load; a high frequency square-wave oscillator with 200mA totem-pole output for driving an isolation transformer; and a second bandgap comparator with latching crowbar to protect against overvoltage faults while starting or running.The SG1540 is specified for operation over the full military ambient temperature range of -55°C to 125°C. The SG2540 is character-ized for the industrial range of -25°C to 85°C, and the SG3540 is designed for the commercial range of 0°C to 70°C.