LR745

Features:

· 25V to 450V operating input voltage range
· Compatible with industry standard PWM ICs. See application notes AN-H28 and AN-H29.
· Output current limiting
· For PWM ICs with start-up threshold voltage of 13.9V to 18.8V
· Very low power consumption after start-up


Application

· Notebook and Laptop computers
· Telecommunication power supplies
· Battery chargers
· Motor controller


Specifications

Input Voltage                                                                           450V
Output Voltage                                                                          25V
Operating and Storage Temperature                     55  to 150
Soldering Temperature*                                                         300
*Distance of 1.6mm from case for 10 seconds


Description

The Supertex LR745 is a high input voltage SMPS start-up circuit.

The LR745 is ideally suited for use with industry standard low voltage PWM ICs having start thresholds of 13.9V to 18.8V. It allows the PWM ICs to be operated from rectified 120V or 240VAC lines, and eliminates the use of power resistors often used for this purpose. The internal circuitry of the LR7 allows the PWM ICs to operate at a V_CC 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 the startup period. After start-up, the internal high voltage line is disconnected from the IC thereby reducing the continuous power dissipation to a minimum.