LR8K4-G

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 V₀₊ 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 10 μA, is connected to the ADJ pin. This increases V₀₊ by a constant voltage of 10 μA times R₂. LR8 provides both current and temperature limiting. The output current limit is typically 20 mA and the minimum temperature limit is +125℃. An output shortcircuit current will therefore be limited to 20 mA. 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 applications, LR8 turns off when an external voltage greater than the output voltage of the LR8 is applied to V₀₊ of the LR8. To maintain stability, a bypass capacitor of 1.0 μF or larger and a minimum DC output current of 500 μA are required. LR8 is available in TO-243AA (SOT-89), TO-252 (DPAK) and TO-92 packages.

Applications

• Offline SMPS startup circuits
• Adjustable high-voltage constant current source
• Industrial controls
• Motor controls
• Battery chargers
• Power supplies

Key features

• 13.2 - 450V Input Voltage Range
• Adjustable 1.20 - 438V Output Regulation
• 5% Output Voltage Tolerance
• Output Current Limiting
• 10 μA Typical ADJ Current
• Internal Junction Temperature Limiting