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LR745
  • LR745
  • LR745

LR745

In Production

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 13.9 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....

Microchip Technology LR745 Product Info

16 April 2026 0

Parameters

+Vin min (V)

35

+Vin max (V)

450

Vout min (V)

13.9

Vout max (V)

18

Output Current (mA)

3

Dimming

N/A

Parallelable

N/A

Package

SOT-89, TO-92

Features

Trimmable Output, Higher Peak Current Capability

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

Description

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 13.9 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.

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