The TL431 is a three-terminaladjustable regulator series with aguaranteed thermalstability overapplicable temperature ranges. Theoutput voltage may be set to anyvalue between Vref and 36 volts withtwo external resistors. These devicehave a typical dynamic:outputimpedance of 0.272,Active outputsharpcircuitry provides a veryturn-on characteristic, making thesedevices excellent replacement forzener diodes in many applications.