The AMS421 is a four-terminal adjustable open collector shunt regulator with guaranteed temperature stability over the entire range of operation. The output voltage can be set to any value between 0.5V (VREF) and 15V by adding two external resistors. The AMS421 features 0.25% initial tolerance, low dynamic output impedance and operates over a wide current range. Due to the sharp turn-on characteristics this device is an excellent replacement for Zener diodes in many applications. AMS421 is available 5 pin SOT-23 packages.