LR645

LR645 is a high input voltage, low output current linear regulator. It has a 3-terminal fixed output voltage version available in TO-92, TO-220 and SOT-89 packages, as well as an adjustable voltage version available in an 8-lead SOIC package. The 3-terminal version functions like any other low voltage 3-terminal regulator except it allows the use of much higher input voltages. When used in a SMPS start-up circuit, it eliminates the need for large power resistors. In this application, current is drawn from the high voltage line only during start-up. Only leakage current flows after start-up, thereby reducing the continuous power dissipation to a few milliwatts. The adjustable voltage version allows trimming of the output voltage from 8.0 to 12V. This version can also be connected to an external depletion mode MOSFET for increased output current. When used in conjunction with depletion mode MOSFET DN2540N5, an output current of up to 150mA is achieved.