SG1540 Datasheet, PDF (1/6 Pages) Microsemi Corporation – OFF-LINE START-UP CONTROLLER

SG1540/SG2540/SG3540
OFF-LINE START-UP CONTROLLER
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.
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.
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
HIGH RELIABILITY FEATURES - SG1540
♦ Available to MIL-STD - 883
♦ LMI level "S" processing available
BLOCK DIAGRAM
4/90 Rev 1.1 2/94
Copyright © 1994
LINFINITY Microelectronics Inc.
1
11861 Western Avenue ∞ Garden Grove, CA 92841
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