LR645
High Input Voltage SMPS Start-up / Linear Regulator
Features
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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
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.
Applications
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Off-line SMPS startup circuits (pulse loads)
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Low power off-line regulators
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Regulators for noisy inputs
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.
Block Diagram
V
IN
LR645
V
OUT
TRIM
–
+
GATE
GND
SUPERTEX [ Supertex, Inc ]
