LR8
High Input Voltage
Adjustable 3-Terminal Linear Regulator
Features
General Description
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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.
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
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Off-line SMPS startup circuits
Adjustable high voltage constant current source
Industrial controls
Motor controls
Battery chargers
Power supplies
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 (DPAK), and TO-92 packages.
Typical Application Circuit
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VOUT
VIN
VIN
VOUT
ADJ
LR8
R1
C2
C1
R2
*Required for conditions where VIN is less than VOUT.
RLOAD
