LR8K4

Polarity : Positive
Maximum Operating Temperature : + 85 C
Mounting Style : SMD/SMT
Output Type : Adjustable
Package / Case : TO-252
Line Regulation : 0.01 % / V
Load Regulation : 3 %
Input Voltage MAX : 480 V
Output Current : 20 mA
Output Voltage : 1.26 V


Features:

` 12V to 450V input voltage range
` Adjustable 1.20V to 440V output regulation
` 5% output voltage tolerance
` Output current limiting
` 10A typical ADJ current
` Internal junction temperature limiting


Application

· Off-line SMPS startup circuits
· Adjustable high voltage constant current source
· Industrial Controls
· Motor controls
· Battery chargers
· Power supplies


Specifications

VIN Input Voltage                                                                   -0.5V to +480V*
Output Voltage Range                                                            -0.5V to +470V
Operating Ambient Temperature Range                                  -40 to +85
Operating Junction Temperature Range                                -40 to +125
Storage Temperature Range                                                 -65 to +150
*Voltages referenced to ADJ.


Description

The Supertex LR8K4 is a high voltage, low output current, adjustable linear regulator. It has a wide operating input voltage range of 12V to 450V. The output voltage can be adjusted from 1.20V to 440V provided that the input voltage is at least 10V 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 V_OUT 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 10A is connected to the ADJ pin. This increases VOUT by a constant voltage of 10A times R2.

The LR8K4 has current limiting and temperature limiting. The output current limit is typically 15mA and the minimum temperature limit is 125°C. An output short circuit current will therefore be limited to 15mA. 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 V_OUT of the LR8. To maintain stability, a bypass capacitor of 1.0F or larger and a minimum DC output current of 500A are required.

The LR8K4 is available in TO-92, TO-243AA (SOT-89), and TO-252 (D-PAK) packages.