Identifying the Anode and the Cathode of Diode with an Ohmmeter

Before attempting to test a good or defective diode, one very important thing to consider is its terminals or electrodes. These electrodes are anode (A), positive current-carrier and cathode (K), negative current-carrier. Following are some points to consider in determining the electrodes of a diode.

1. Cathode and anode markings are displayed on the body of the diode, as shown in the illustration.

   

   Schematic Symbol of diode. The white band represents Cathode.

2. Sometimes, markings are worn out, in this case use a multimeter to determine the electrodes of diode. The battery inside the multimeter is used to apply forward or reverse bias to diode. In forward bias, the positive post of the battery is connected to the anode, and the negative post is connected to the cathode. In reverse bias the positive post of the battery is connected to the cathode and the negative post is connected to the anode.
   
3. In some brand of multimeter like SANWA, the negative terminal of the battery is connected to the red test probe while the positive terminal is connected to the black test probe. Therefore, to apply forward bias to diode you have to connect the red test probe to the cathode (K) and the black test probe to the anode of the diode. Throughout our discussion, we will use SANWA as our multimeter.

   

   Using a SANWA multimeter, when the pointer needle deflects to the right, the diode is in forward bias. Therefore the electrode connected to the red test probe (positive test probe) is the CATHODE (K), while the electrode connected to the black test probe (negative test probe) is the ANODE (A).

Using a SANWA multimeter, when the pointer needle did not deflect, the diode is in reverse bias. Therefore the electrode connected to the red test probe (positive test probe) is the ANODE (A), while the electrode connected to the black test probe (negative test probe) is the CATHODE (K).