Step-by-Step Tutorial on How to Test Diodes

Diodes are widely used in circuit design in order to control the system current flow in one direction. They are two-terminal electronic devices; one is an anode terminal, and the other is a cathode terminal.

In this article, we will be discussing how to test a diode with a multimeter, which includes a digital multimeter in diode mode, ohmmeter mode, and an analog multimeter. Please be noted that all the power should be off while testing the diode.

1. Using a diode mode digital multimeter to test a diode

Turn a digital multimeter to diode mode.

Step. 1 Make the forward-biased connection

Connect the red probe of the digital multimeter to the anode terminal of the diode and the black probe to the cathode terminal. For a PN junction diode, the display voltage value should be around 0.6 to 0.7 (volts) as it is the voltage drop of a normal forward-biased diode.

Step. 2 Reverse the connection

Connect the red probe of the digital multimeter to the cathode terminal of the diode and the black probe to the anode terminal. For a PN junction diode, the display voltage value should be OL (open circuit) as the diode is reverse-biased.

2. Using an ohmmeter mode digital multimeter to test a diode

Turn a digital multimeter to ohmmeter mode.

Step. 1 Make the forward-biased connection

Connect the red probe of the digital multimeter to the anode terminal of the diode and the black probe to the cathode terminal. Since the PN junction diode is forward biased, the resistance (which is shown on the display) should be nearly zero.

Step. 2 Reverse the connection

Connect the red probe of the digital multimeter to the cathode terminal of the diode and the black probe to the anode terminal. At this time, the resistance (which is shown on the display) should be extremely high since the diode is reverse-biased. Hence you should read a high value or OL (open circuit) on the display.

3. Using an analog multimeter to test a diode

To test a diode with an analog multimeter is similar to that with a digital multimeter in ohmmeter mode.

Step. 1 Make the forward-biased connection

Turn the selector to a low resistance value. Connect the positive terminal of the analog multimeter to the anode of the diode and the negative terminal to the cathode. The indicator of the multimeter should point to nearly zero resistance as the diode is forward-biased.

Step. 2 Reverse the connection

Turn the selector to a high resistance value. Connect the positive terminal of the analog multimeter to the cathode of the diode and the negative terminal to the anode. The indicator of the multimeter should point to nearly infinite resistance as the diode is reverse-biased.

In summary, it is easy to expect the correct testing results from the I-V curve of a diode. When the diode is forward-biased, the voltage drop should be around 0.6 to 0.7 volts, while there is nearly no resistance. When the diode is reverse-biased, the voltage drop is almost zero before breakdown, while the resistance is nearly infinite.

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