Testing Diodes

Diode testing.

To test a diode you need to use a multimeter set to Ohms range. A working diode should only allow current to flow in one direction; Anode to Cathode. The most reliable way to test a diode is with the ‘Diode test’ position on your multimeter. In this position a higher voltage is used and the meter shows the voltage drop required to push through the boundary layer.

When testing diodes in the ohms range, a measurement of more than 2K needs to be set, because 2K is not enough to measure the diode, you will only get a reading of infinity. Using the diode test range again only work in Anode-> Cathode direction, because Cathode -> Anode is blocked.

we built a circuit with a 1K resistor and use a 12v battery supply and measured the voltage drops across the resistor and the Diode, the voltage drop across the resistor was around 12.7v, the VD across the diode was 0.65v, the amp flow through the diode was 0.01amps. we then took a voltage reading from the battery which gave us13.39v, lastly we added the voltage drop across the resistor and the diode- VDr + VDd= 13.35V. The rules of electricity apply here because the available voltage from the supply was equal to the voltage drop across the resistor and the diode, which are the components of the circuit, and in a series circuit like this was, the voltage is maintained through-out the circuit.

If you swap the diode for an LED you get a bigger voltage drop across the LED because the LED uses more voltage then the diode because it has to light up, whereas the diode doesn’t have to. Apart from that everything else in the circuit is the same.