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DS20005384B-page 1

Features

• Accepts Inputs from 15 to 450V

• Output Currents: Up to 3.0 mA Continuous,

30 mA Peak

• Supply Current Typically 50 μA

• Line Regulation Typically 0.1 mV/V

• Output Can Be Trimmed from 8.0 to 12V

• Output Current Can be Increased to 150 mA 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 8.0V 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 150 mA 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.

LR645

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