Testing Diodes

  While most of the calculations on electrical circuit are done with conventional current- means that current flow is from positive to negative, Electron flow is actually what happens that electrons go from negative to positive, because they are attracted to the positive charges. Bases on this principal, a semiconductor device called diode is constructed, which only allows current to go only one way forward biased. Apparently, positive charges of missing electrons and electrons are pushed oppositely from the positive and the negative, towards the middle boundary layer. The positive charges are missing electrons so they have "holes" available for flowing through, because the electrons don't stop there but keep being pushed by the negative. A current can flow through a "forward biased" diode because of this.
In a "reversed bias" situation, current can not flow when Positive is connected to the Cathode, that the positive is more likely to attract the electrons side of the diode rather than pushing them.
   When "testing diode" resistance becomes practical, there are 2 ways.
  When testing a diode using Ohms meter, make sure that the meter is "strong enough" to push the holes and the electrons through the "boundary layer", in order to be able to "turn on" the diode. Some small multimeter is incapable of this, we either use a stronger meter or, switch to "old" analog meter that is actually capable.
   Remember when we check the rectifier diodes out of the alternator, we did use the diode test setting on the multimeter. What the meter does is using a higher voltage to push the diode, then it will record the voltage drop required to do this, hence this VD is correspondent to the diode's resistance. By measuring the diode in both directions, from anode to cathode, the resistance should be low because it is possible to flow through the diode. The resistance from cathode to anode should be infinity indicating that the blocking is functional.
  During our assessment, we must build a simple diode circuit incorporating a 1k Ohm resistor in front in series. A small diode like an LED has very little resistance itself hence the current flowing through it would be huge, eventually will "kill" it. Therefore, a big resistance is added to control the current flowing in this series circuit. Later on, a LED replace the current diode. Because the LED is a light-emitting device, hence it needs higher resistance to draw enough voltage to shine. The rule of electricity is again in action to tell that in a series circuit, the component with the most resistance will require most of the Supply Voltage to push the flow through.