Circuit lets you measure zener voltages and test LEDs

by Vladimir Oleynik @ edn.com: To measure a zener diode’s breakdown voltage, you need a dc voltage source whose voltage exceeds that of the zener voltage. In Figure 1, resistor RSER provides voltage drop between VIN and VZEN. In any case, VIN should exceed VZEN. Resistor RSER must provide current, IZEN,...