Vermes
Advanced Member level 4
It is a simple system for testing and measuring the Zener voltage or forward voltage of semiconductor diodes. Accuracy of this device is not very high and it depends on the kind of used voltmeter. Current stabilizing system consists of a standard application LM334. If your mains transformer provides too high secondary voltage, you have to lower it to 40V (maximum for LM334). In that case you can add LM317 operating in standard application system.
You can adjust the tester using potentiometer R5. When the device is run for the first time, set +40V and choose the resistor R6 so that the current passing through tested Zener diode is approximately 10mA. Resistor R6 can be replaced with two or three constant resistors, then the resistance should be equal 10ohm.
You can make the whole system more simple and remove +5V power supply and stabilizer LM317, but only if you use mains transformer of lower secondary voltage and traditional meter instead of electronic milivoltmeter.
Link to original thread (useful attachment) - Tester diod Zenera ze źródłem prądowym LM334