Testing Diodes

TTEC 4841 - Electrical and Electronics- Practical

26/8/2011 tuesday

start = 1.00pm finsh = 4.30pm

In todays task we learned how to measure diodes with , diodes test.

First thing we had to do was to identify the direction of flow through the diodes.

which is Anode, catthode, and current flow.

Then we moved on by measuring the resistance (ohms) of the diodes in both directions using the 2k ohms on multimeter.

Anode to cathode=  infinity ohms
Cathode to anode=  infinity ohms

 Then we checked the voltage supplied at the meter probes in the ohms position, with another meter set on Dc volts while the meter set on 2k ohms position,

= 0.24 v

Is this enough voltage to theoretically push through the bindery layer of the diode and get an accurate reading ?  NO

• Did the ohms measurement work? no beacuse theres not enough voltage pushing through the bindery layer of the diode.

Then we set our multimeter to diode to test the position using.

• Anode to cathode = 0.624 v
• Cathode to anode = infinity v

This shows that it will be from anode to cathode the is a pathway but from cathode to anode the is no electricity crossing.

Then we Build a circuit with a diode and resistors. we buld the circuit with a 1kohms ( 1000 ) resistors and used 12 volts supply.

• Measure the voltage drop across the resistor ( R ) = 11.87 v
• measure the voltage drop across diode ( D ) =  0.56 v
• measure the amp flow through the diode = 0.00 a
• measure the available voltage at supply ( Vs ) = 12.44 v
• add the voltage drop across R and D .  VDr + VDd = 12.43v

Then we applied the rules of electricity? The voltage drop in the resistor is the highest in the circuit which that leves a small amount of voltage for the diodes, so with the amount of small voltage left for current to flow in.

Then we changed the resistance by placing the resistor with a higher value resistor to the circuit.

• what size resistor did you put in = 1 k
• measure the voltage drop across R = 11.72 v
• measure the voltage drop across D = 0.68v
• measure amp flow through D 0.02 amp

The resistance R and D goes higher as the amps stays the same.

Then we test an LED ( ligh emitting diode ) with a meter in the diode test posistion to measure the LED in both Directions.

Anode to cathode = 2.32v
Cathode to anode = infinity v

Then we compare the voltage drop of a normal diode and an LED.? The voltage in LED is higher because the voltage is used to push mps through the LED but in diode theres no current flow so theres no amp flowing through.

Then we build a circuit with an LED

• measure the voltage drop across R = 10.30 v
• measure the voltage drop across D = 1.84 v
• measure amp flow through LED = infinity
• measure the available voltage At Vs = 12.15 v
• Add the voltage drop R+D = 12.14 v

This showed us that the voltage drop in LED is higher becasue LED has more resistance while its turned on.