The APL1431L is a 3-terminal low voltage adjustable precision reference with specified thermal stability over applicable commercial temperature ranges . Output voltage may be set to any value between VREF (1.24 V) and 20 V with two external resistors (see Figure 2) . When used with an photocoupler , the APL1431L is an ideal voltage reference in isolated feedback circuits for 1.24V to 12V switchingmode power supplies . This device has a typical output impedance of 0.1 . Active output circuitry provides a very sharp turn-on characteristic , making the APL1431L excellent replacements for zener diodes in many applications , including on-board regulation and adjustable power supplies .