How do you test a rectifier with a multimeter

How do you test a rectifier with a multimeter

A diode is a semiconductor device that allows current to flow in only one direction. It is often called a rectifier because it "rectifies" alternating current and converts it into pulsating direct current. Diodes are widely used in the circuits of household appliances, such as microwave ovens. Together with a capacitor, the microwave diode doubles the voltage of the transformer that supplies current to the magnetron (the element that produces the microwave radiation).

On a circuit diagram, the symbol for a diode is a triangle on a straight line, with its apex pointing in the direction of current flow. When the diode is operating, only very little current flows in the opposite direction, preferably none at all. One end of the diode with the triangle pointing is the negative or cathode terminal and the opposite end is the positive or anode terminal. It is important to note the polarity of the diode, because if it is placed in a circuit in the opposite direction, it will not work.

If the current flowing through the diode exceeds its capacity, a short circuit can occur and the diode will not be able to block the reverse flow of current. The circuit inside the diode may also open due to age or wear, if this happens the diode will not allow current to flow in either direction. In both cases, the diode is defective and must be replaced. You can check it with a multimeter.

From Science magazine

TL; DR (too long; unreadable).

To test the diode, you can use one of two methods. If you have a meter with a diode test function, you can use it. Otherwise, you can set the meter to measure resistance.

Testing a rectifier with a diode function.

If your multimeter has a diode function, one of the scale settings has a mark similar to the diode symbol. When this setting is selected, a voltage appears across the test leads and the meter registers a voltage drop when the lead touches the diode terminals. In the forward direction, the voltage drop is typically between 0.5 and 0.8V. In the opposite direction, no current flows, so the meter displays 0 or OL, which means open loop.

To perform the test, first make sure that the circuit is not connected and that all capacitors in the circuit are discharged. It is not necessary to remove the diode from the circuit when performing this step. First, connect the negative terminal of the meter (usually black) to the cathode of the diode and the positive (red) terminal to the anode. Note the reading, which should be between 0.5 and 0.8 volts. If it is close to 0, the diode is defective. Now reverse the leads. If you get a reading of 0 or OL then there is nothing wrong with the diode. If you get the same voltage value, then the diode is shorted and not working.

Testing diodes with an ohmmeter

When performing a resistance test, the diode must be removed from the circuit. Before doing so, the power supply must be disconnected and all capacitors in the circuit must be discharged. This is especially important when testing microwave diodes, as high voltage microwave capacitors can cause strong discharges.

Set the multimeter to measure resistance (Ω) by touching the black (negative) lead to the cathode and the red (positive) lead to the anode. In this configuration, the diode is directly biased and you should get a resistance value between 1KΩ and 10MΩ. Now place the leads on the opposite terminals. The diode is now reverse biased and should read infinity or OL. If the reading is the same in both directions, the diode is faulty.