LR745 Просмотр технического описания (PDF) - Microchip Technology

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LR745

High-Input Voltage SMPS Start-up

Microchip Technology 

LR745

High-Input Voltage SMPS Start-up

Features

• Accepts inputs from 35 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

Description

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

LR745 is ideally suited for use with industry standard

low-voltage, Pulse-Width Modulation (PWM) ICs hav-

ing start thresholds of 13.9 to 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 the start-up period. After start-up,

the internal, high-voltage line is disconnected from the

IC, thereby reducing the continuous power dissipation

to a minimum.

 2015 Microchip Technology Inc.

DS20005394A-page 1

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