LR645

Features

Accepts inputs from 15V 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 8.0V 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

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General Description

The Supertex LR645 is a high input voltage, low output

current linear regulator. It has a 3-terminal fixed output voltage

version 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 functions like any

other low voltage 3-terminal regulator except it allows the use

of much higher input voltages. When used in a SMPS start-

up circuit, it 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 8.0V to 12V. This version can also be connected

to an external depletion mode MOSFET for increased output

current. When used in conjunction with Supertex depletion

mode MOSFET DN2540N5, an output current of up to 150mA

is achieved.

Block Diagram

High Input Voltage SMPS Start-up / Linear Regulator

V

OUT

GND

GATE

V

IN

TRIM

+

–

LR645

Caution!

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.