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LR745
High Input Voltage SMPS Start-up
Features
► Accepts inputs from 35V to 450V ► Output current limiting ► For PWM ICs with start-up threshold voltage of
13.9 - 18.0V ► Very low power consumption after start-up
Applications
► Notebook and laptop computers ► Telecommunication power supplies ► Battery chargers ► Motor controllers
General Description
The Supertex LR745 is a high input voltage SMPS startup circuit. The LR745 is ideally suited for use with industry standard low voltage PWM ICs having start thresholds of 13.9 - 18.0V. It allows the PWM ICs to be operated from rectified 120 or 240VAC lines, and eliminates the use of power resistors often used for this purpose.
The internal circuitry of the LR745 allows the PWM ICs to operate at a VCC voltage below their start threshold voltage after start-up. The auxiliary voltage can be less than the start threshold voltage, which allows for improved efficiency. Current from the high voltage line is drawn only during .