The Principle of Testing Diodes with a Multimeter
When you use the diode setting on a multimeter, the numbers displayed on the screen tell a little story about the electronic world:
For forward bias measurement, the display shows the forward voltage (0.5-0.7V for silicon diodes, 0.2-0.3V for germanium diodes).
For reverse bias measurement, the display shows the resistance value (ideally infinite).
A beep indicates good forward conduction.
Hidden Information in Measurement Data
These seemingly simple numbers hide important clues:
Health Status: Forward Excessive voltage drop may indicate aging; insufficient voltage drop may cause breakdown.
Material type: Silicon and germanium diodes have characteristic voltage differences.
Polarization determination: The pin connected to the red probe corresponds to the diode's positive terminal.
Abnormal conditions: Bidirectional conduction indicates a short circuit; bidirectional non-conductivity may indicate an open circuit.
Practical Measurement Techniques Mastering diode testing like an experienced electrician:
Digital multimeters are more accurate than analog multimeters.
Online measurements require power off and discharge.
Light-emitting diodes (LEDs) require higher test voltages.
Zen regulator diodes require an adjustable power supply for testing.
High-power diodes are recommended to be tested with a dedicated testing instrument.
