The TL431/TL431A are three-terminal adjustable regulatorseries with a guaranteed thermal stability over applicabletemperature ranges. The output voltage may be set to anyvalue between VREF (approximately 2.5 volts) and 36 voltswith two external resistors These devices have a typicaldynamic output impedance of 0.2Î. Active output circuitryprovides a very sharp turn-on characteristic, making thesedevices excel lent replacement for zener diodes in manyapplications.