LR645 Datasheet, PDF (1/16 Pages) Supertex, Inc – High Input Voltage SMPS Start-up / Linear Regulator

LR645
High-Input Voltage SMPS, Start-up/Linear Regulator
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.
 2015 Microchip Technology Inc.
DS20005384A-page 1