The LM317MDCY is a voltage regulator IC (integrated circuit) manufactured by Texas Instruments. It is a positive adjustable regulator with one output, and has a maximum current of 500mA. It comes in the SOT-223-4 package, which has a 4-pin, surface-mount package with an extended temperature range. The LM317MDCY can provide output voltages from 1.2V to 24V and features over-current protection, thermal shutdown, and output current limiting protection. It is suitable for use in computers, consumer electronics, industrial equipment, and other applications.