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Question

How do you test a diode rectifier?


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Solution

  1. A diode is a semiconducting device that permits the current to pass in only one direction.
  2. A forward-biased diode acts as a closed switch, allowing current to flow, for silicon diode voltage drop is 0.7V. For germanium it is 0.25V to 0.3V.
  3. A diode is best tested by checking the voltage drop across the forward-biased diode.

To test a diode rectifier, connect the anode terminal of the diode to the red probe of the multimeter and the cathode to the black probe, then current flows through the diode and the multimeter shows a small voltage drop, but if reverse the diode terminals, no current will flow, the multimeter will show OL which represents an open circuit.

Use Diagram:

A diode is a tiny component that only permits one direction of electric current flow in an electrical circuit. Low resistance in one direction and high resistance in the other is how it operates. A diode, which is typically made of a semiconductor material (such as silicon in Group IV of the periodic table or selenium in Group VI of the periodic table), must occasionally be tested to ensure it is functioning properly. A digital or analog multimeter that measures in ohms Ω or volts can be used to examine the health of a typical diode.

  1. Turn off the power to the diode. Testing a diode when it is connected to a circuit will produce inaccurate results and is extremely dangerous. Turn off the power supply, which could be a battery or an electrical outlet, or remove the diode entirely from the circuit.
    You can reduce your chance of an explosion or an electric shock by discharging the capacitors to release any excess voltage they may be holding.
  2. The selection switch should be set at low resistance. It will cost roughly one thousand. Low resistance on the multimeter allows some current to pass through without overtaxing the diode.
    The dial in the middle of the multimeter is the selecting switch.
  3. To find out if the diode is healthy, check the reading on the meter. If your diode is forward biased and functioning properly, the meter will read between 1 and 100. The measurement on the meter should indicate infinite resistance if the diode is reverse biased, indicating that it is open. For either type of diode, a decreased resistance indicates a shorted diode that has to be replaced. You should change your diode in either of these scenarios.
    Make sure the leads are firmly clipped onto the diode if there is no reading at all.
  4. Test your leads on a fresh battery to see whether they are working properly. Attach the red clip to the positive end of the wire and the black clip to the negative end while the multimeter is in voltage mode. You need new leads if the reading doesn't match the battery voltage.
  5. Put the black lead on the anode and the red lead on the cathode, respectively. Now that it is reverse biased, there is no current passing through. The dial should be set to high resistance (about 100 K) before moving the leads into their new places for best results.
    High resistance is required in this case because reverse bias is designed to prevent any electricity from flowing through (or to "resist" it).
  6. Look for an open loop reading (OL, or the infinity symbol). This indicates that the diode is operating properly. The diode has to be replaced if it displays a low resistance reading. It may be as simple as switching out regular batteries to replace a diode. To connect it to the circuit, you might need to lightly solder the ends.

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