Diodetesting

Diodetesting, or diode testing, is the practice of verifying the function and characteristics of diodes using electrical measurement equipment. It is commonly performed with a digital multimeter that includes a diode test function, but dedicated diode testers or curve tracers may also be used.

Most meters apply a small test current and measure the forward voltage drop when the test leads are connected to the diode’s anode and cathode. A healthy silicon diode typically shows a forward drop of about 0.6 to 0.7 volts; germanium diodes are lower, around 0.2 to 0.3 volts, and Schottky diodes can be even lower. In reverse bias, the meter should indicate no conduction or a very high resistance, up to the diode’s reverse breakdown voltage. LEDs behave similarly in test mode but with higher forward voltages depending on color and construction.

Testing in-circuit versus out-of-circuit matters. For accuracy, it is often best to remove at least one lead from the circuit to avoid parallel paths through other components. In-circuit testing can yield misleading results due to surrounding resistors, LEDs, transistors, or other diodes.

Special cases include Zener diodes and LEDs. In diode-test mode, a Zener diode will show a forward drop when biased forward, but its reverse breakdown rating is not tested without applying a controlled reverse voltage and current-limiting source. LEDs may display a forward voltage corresponding to their color, but some meters limit current and may not provide a reliable LED test.

Limitations exist: some diodes, especially in complex circuits or high-speed parts, may not test reliably with a basic meter. Always ensure circuits are de-energized and discharge capacitors before testing.

See also: diode, silicon diode, Zener diode, LED, multimeter, diode tester.