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What is a Diode ? An electronic component that allows the current flow in one direction only. It has with two electrodes called the anode and the cathode. Most diodes are made with semiconductor materials such as silicon, germanium. ü Application of diode • Rectification : A rectifier changes AC (Alternating Current) to DC (Direct Current ) This is the most important application of diodes. 17/11/2014 Numeral Systems page. Page 3 3 1/22/2022

Types of Diodes • • Normal Diodes Light-Emitting Diodes (LEDs) Schottky Diodes Zener Diodes 17/11/2014 4 page 4

How a diode works 17/11/2014 Numeral Systems page Page 5 5 1/22/2022

Forward Operation In forward operation the anode connected to the positive electrode of the source and the cathode connected to the negative electrode of the source. In this situation the current flows in the circuit. The current flows in the Circuit. Numeral Systems 17/11/2014 1/22/2022 page. Page 66

Reverse Operation In reverse operation the anode connected to the negative electrode of the source and the cathode connected to the positive electrode of the source. No current ( very small ) flows in in the circuit. Numeral Systems 17/11/2014 1/22/2022 page. Page 77

curve for a real diode. 17/11/2014 Numeral Systems page. Page 88 1/22/2022

Forward and Reverse Operation • Practical Exercise : - 17/11/2014 page 9

Partner Work 17/11/2014 Numeral Systems page 1010 1/22/2022 Page

Partner Work In short sentence: Q 1 : - Define a diode ? q A diode is a electronic component that allows the current flow in one direction only. Q 2 : - Draw a symbol of diode ? Q 3 : - what is the difference between forward biased and reverse biased ? q In forward biased the current flows in the circuit. q In reverse biased no current flows in the circuit. 17/11/2014 Numeral Systems page 11 1/22/2022 Page 11

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Example ( 1 ) : - Assume the diode in the circuit below is ideal. Determine the value of ID if : a) VA = 5 volts (Forward Bias) b) VA = -5 volts (Reverse Bias) Numeral Systems 17/11/2014 1/22/2022 Page 13 page 13

Solution : a) With VA > 0 the diode is in forward bias and is acting like a perfect conductor so: ID = VA / RS = 5 V / 50 = 0. 1 A b) With VA < 0 the diode is in reverse bias and is acting like a perfect insulator, therefore no current can flow and ID = 0. Numeral Systems 17/11/2014 1/22/2022 Page 14 page 14

Group Work 17/11/2014 page 15

Group Work Assume the diode in the circuit below is ideal. Determine the value of ID if : a) VA = 10 v (Forward Bias) b) VA = -10 v (Reverse Bias) Numeral Systems 17/11/2014 1/22/2022 Page page 1616

Group Work Solution : a) With VA > 0 the diode is in forward bias and is acting like a perfect conductor so: ID = VA / RS = 10 V / 80 = 0. 125 A b) With VA < 0 the diode is in reverse bias and is acting like a perfect insulator, therefore no current can flow and ID = 0. 17/11/2014 Numeral Systems page 1717 1/22/2022 Page

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Summary What do you remember from Numeral Systems 17/11/2014 1/22/2022 Page 19 page 19