How to Test a Diode: The diode is a two terminal semiconductor device which allows the current flow only in one direction. These are found in many applications such as rectifiers, clampers, clippers and so on.
Testing of a Diode using Digital Multimeter:
The diode testing using a digital multimeter (DMM) can be carried in two ways as there are two modes available in DMM to check the diodes such as diode mode and ohmmeter mode.
Diode Mode Testing:
Step by Step Instructions:
1. Identify the diode terminals (anode and cathode).
2. Keep the digital multimeter (DMM) in diode checking mode by rotating the central knob to the place where the diode symbol is indicated. In this mode multimeter is capable to supply a current of 2mA approximately between the test leads.
3. Connect the red probe to the anode and black probe to the cathode. This means diode is forward-biased.
4. Observe the reading on the meter display. If the displayed voltage value is in between 0.6 to 0.7 (since it is silicon diode) then the diode is healthy and perfect. For germanium diodes this value is in between 0.25 to 0.3.
5. Now reverse the terminals of the meter that means connect the red probe to cathode and black to anode. This is the reverse biased condition of the diode where no current flows through it. Hence the meter should read OL (which is equivalent to open circuit) if the diode is healthy.
6. If the meter shows irrelevant values to the above two conditions, then the diode is defective.
DIODE SHORT OR OPEN:
The diode defect can be either open or short. Open diode means diode behaves as an open switch in both reverse and forward-biased conditions. So, no current flows through the diode. Therefore, the meter will indicate OL in both reverse and forward-biased conditions.
Shorted diode means diode behaves as a closed switch so the current flows through it and the voltage drop across the diode will be zero. Therefore, the multimeter will indicate zero voltage value, but in some cases it will display a very little voltage as the voltage drop across the diode.