 2015 Microchip Technology Inc.

DS20005384A-page 1

LR645

Features

• Accepts inputs from 15 to 450V

• Output currents: up to 3.0mA continuous, 30mA

peak

• Supply current typically 50µA

• Line regulation typically 0.1mV/V

• Output can be trimmed from 8.0 to 12V

• Output current can be increased to 150mA with

external FET

Applications

• Off-line SMPS startup circuits (pulse loads)

• Low power off-line regulators

• Regulators for noisy inputs

Description

LR645 is a high-input voltage, low-output current, linear

regulator that is available in two versions. A 3-terminal,

fixed-output voltage version is available in TO-92, TO-

220 and SOT-89 packages, as well as an adjustable

voltage version available in an 8-lead SOIC package.

The 3-terminal version of LR645 functions like any

other low-voltage, 3-terminal regulator except it allows

the use of much higher-input voltages. When used in a

Switched-mode Power Supply (SMPS), start-up circuit,

LR645 eliminates the need for large power resistors. In

this application, current is drawn from the high voltage

line only during start-up. Only leakage current flows

after start-up, thereby reducing the continuous power

dissipation to a few milliwatts.

The adjustable-voltage version allows trimming of the

output voltage from 8.0 to 12V. This version can also be

connected to an external depletion mode metal–oxide–

semiconductor field-effect transistor (MOSFET) for

increased output current. When used in conjunction

with depletion mode MOSFET DN2540N5, an output

current of up to 150mA is achieved.

WARNING

The LR645 does NOT provide galvanic isolation. When operated from an AC line, potentially lethal voltages can be

present on the IC. Adequate means of protecting the end user from such voltages must be provided by the circuit

developer.

High-Input Voltage SMPS, Start-up/Linear Regulator