We have all had difficulty testing diodes in-circuit. Most DMM’s have a diode Vf function that measures forward drop, but what is the normal voltage drop?

Figure 4 shows an assembled zener-diode-tester circuit. The zener diode under test is On Semiconductor ‘s BZX55C15RL, which has a working voltage of 13.8 to 15.6V. The voltage in Figure 4was measured ...