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LR8 Datasheet, PDF (1/16 Pages) Supertex, Inc – High Input Voltage Adjustable 3-Terminal Linear Regulator
LR8
High-Input Voltage, Adjustable, 3-Terminal,
Linear Regulator
Features
• 13.2 - 450V input voltage range
• Adjustable 1.20 - 438V output regulation
• 5% output voltage tolerance
• Output current limiting
• 10µA typical ADJ current
• Internal junction temperature limiting
Applications
• Off-line SMPS startup circuits
• Adjustable high voltage constant current source
• Industrial controls
• Motor controls
• Battery chargers
• Power supplies
Description
LR8 is a high-voltage, low-output current, adjustable
linear regulator. This regulator has a wide operating
input voltage range of 13.2 - 450V. The output voltage
can be adjusted from 1.20 - 438V, provided that the
input voltage is at least 12V greater than the output
voltage. The output voltage can be adjusted by means
of two external resistors, R1 and R2, as shown in the
typical application circuits. LR8 regulates the voltage
difference between VOUT and ADJ pins to a nominal
value of 1.20V. The 1.20V is amplified by the external
resistor ratio R1 and R2. An internal constant bias cur-
rent, of typically 10µA, is connected to the ADJ pin.
This increases VOUT by a constant voltage of 10µA
times R2.
LR8 provides both current and temperature limiting.
The output current limit is typically 20mA and the mini-
mum temperature limit is 125°C. An output short-circuit
current will therefore be limited to 20mA. When the
junction temperature reaches its temperature limit, the
output current and/or output voltage will decrease to
prevent the junction temperature from exceeding its
temperature limit. For SMPS start-up circuit applica-
tions, LR8 turns off when an external voltage greater
than the output voltage of the LR8 is applied to VOUT
of the LR8. To maintain stability, a bypass capacitor of
1.0µF or larger and a minimum DC output current of
500µA are required.
LR8 is available in TO-243AA (SOT-89), TO-252 (D-
PAK), and TO-92 packages.
 2015 Microchip Technology Inc.
DS20005399A-page 1
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