The LR645 is a high input voltage, low output current, linear voltage regulator available in two versions. 3-terminal, fixed-output voltage versions are available in TO-92, TO220, and SOT-89 packages, as well as adjustable voltage versions in 8-pin SOIC packages.
Block diagram
The 3-terminal version of the LR645 functions like any other low-voltage, 3-terminal regulator, except that it allows the use of higher input voltages. When used in switch-mode power supply (SMPS) starter circuits, the LR645 eliminates the need for high-power resistance. In this application, the current is only extracted from the high voltage line at startup. Only leakage current flows after startup, reducing continuous power consumption to a few milliwatts.
The adjustable voltage version allows the output voltage to be adjusted from 8.0 to 12V. This version can also be connected to an external depletion mode metal oxide semiconductor field effect transistor (MOSFET) to increase the output current. When combined with the depletion mode MOSFET DN2540N5, the output current is up to 150mA.
