What is the voltage of a zener diode recently removed from the scrap box and without any markings? If the reader has no way of knowing this, see the suggestion we found in a 1982 publication. In the figure we have a very simple zener diode tester. What we have is a voltage reducer in which one branch is formed by the 47k resistor and the other by the zener itself. A common intercepted rectifier diode allows to obtain direct current in the test. The meter connected in parallel with the zener diode allows direct reading of this voltage. Note that the current flowing through the zener diode under test is determined by the value of the resistor, standing at a maximum of 2.3 mA for those with lower values. In the 220 V network the resistor must be 100 k with a dissipation of at least 1 W.
