An electrical device like this requires a reverse leakage current of 100nA @ 21V.While the device is operating, the maximum voltage - Zener (Nom) is reduced to 28V.For operation, diode reaches 1.2V @ 200mA at the maximum voltage - Forward (Vf).
1N5255B_T50R Features
reverse leakage current of 100nA @ 21V 100nA @ 21V is the maximum voltage (Tol)
1N5255B_T50R Applications
There are a lot of ON Semiconductor 1N5255B_T50R applications of zener single diodes.