Practical - 24 :- Diode Terminal Identification and Specifications

 Aim

• To visually and practically identify the Anode (+) and Cathode (-) terminals of different types of diodes (e.g., General Purpose Rectifier and LED).

• To record the key electrical specifications of a common rectifier diode like the 1N4007 (and BY127) from its datasheet.

1. 🎯 Experiment Aim

• To visually and practically identify the Anode (+) and Cathode (-) terminals of different types of diodes (e.g., General Purpose Rectifier and LED).

• To record the key electrical specifications of a common rectifier diode like the 1N4007 (and BY127) from its datasheet.

2. 🧰 Apparatus

• Diodes: General Purpose Rectifier Diode 1N4007 (and BY127), one LED (Light Emitting Diode).

• Measuring Instruments: Digital Multimeter (DMM) with Diode Test mode.

• Connecting Leads and a Breadboard (optional).

3. 📝 Terminal Identification Procedure

The Anode is the P-side (positive) and the Cathode is the N-side (negative). Current flows easily from Anode to Cathode.

1. Rectifier Diode (1N4007 (and BY127)):

   • Examine the cylindrical body of the diode.

   • The end marked with a colored band (usually grey or silver) is the Cathode (-) terminal.

   • The other, unmarked end is the Anode (+) terminal.

2. Light Emitting Diode (LED):

• Compare the length of the two leads. The longer lead is the Anode (+).

• The shorter lead is the Cathode (-).

• Alternative Visual Check: The base of the LED often has a small flat edge or cut-out on the rim, which corresponds to the Cathode side.

B. Multimeter Test Method

1. Set the Digital Multimeter (DMM) to the Diode Test (--> |  -- ) mode. 

   
   
   

2. Forward Bias Test (Anode to Cathode):

• Connect the Red Probe (+) of the DMM to one terminal of the diode.

• Connect the Black Probe (-) of the DMM to the other terminal.

• If the diode is correctly connected (forward biased), the DMM will display a small voltage value, typically around 0.6V to 0.7V for a Silicon diode.

• The terminal connected to the Red Probe is the Anode (+), and the terminal connected to the Black Probe is the Cathode (-).

3. Reverse Bias Test (Confirmation):

   • Reverse the DMM probes.

   • The DMM should display "OL" (Over Limit/Open) or "1", indicating infinite resistance and no current flow (or a very small minority carrier current, which the DMM does not read). This confirms the identification.