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LR8N3

High Input Voltage Adjustable 3-Terminal Linear Regulator

Supertex Inc 

LR8

High Input Voltage

Adjustable 3-Terminal Linear Regulator

Features

► 13.2V to 450V input voltage range

► Adjustable 1.20V to 440V 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

General Description

The Supertex LR8 is a high voltage, low output current,

adjustable linear regulator. It has a wide operating input

voltage range of 13.2V to 450V. The output voltage can be

adjusted from 1.20V to 440V 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. The

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

current of typically 10µA is connected to the ADJ pin. This

increases VOUT by a constant voltage of 10µA times R2.

The LR8 has current limiting and temperature limiting. The

output current limit is typically 20mA and the minimum

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 keep the junction temperature from

exceeding its temperature limit. For SMPS start-up circuit

applications, the 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.

The device is available in TO-243AA (SOT-89), TO-252 (D-

PAK), and TO-92 packages.

Typical Application Circuit

*

VOUT

VIN

VIN VOUT

ADJ

LR8

R1

C1

C2

RLOAD

R2

*Required for conditions where VIN is less than VOUT.

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