LM317 Adjustable Down To 0 V Voltage Regulator

This is an adjustable voltage regulator using the LM317 three-terminal adjustable-output voltage regulator IC. With a negative DC voltage source the output voltage can be adjusted all the way to 0 V through the aid of a negative voltage reference. The voltage reference sets the lower terminal of the variable resistor to -1.25 V. This counters the 1.25 V reference voltage from the output (Vout) to adjustment (ADJ) pins, thus making the minimum voltage 0 V.