Diodes Stacy Hadiwidjaja Thursday, 25 April 13 What are diodes? - PowerPoint PPT Presentation

Diodes Stacy Hadiwidjaja Thursday, 25 April 13

What are diodes? Devices that allow an electric current to pass in one direction only. (a.k.a. forward direction) Blocks the current in the opposite direction (a.k.a. reverse direction) Form of Rectifier Electronic valve - sort of Used to convert AC to DC Thursday, 25 April 13

2 Main Types Semiconductor diode Made by a crystalline piece of a semiconductor material connected to 2 electrical terminals. Used in all areas of the electronics industry from electronics design through to production and repair. Used in small signal applications, high current and voltage, light emission and detection, microwave applications, etc. Vacuum tube diode Vacuum tube with 2 electrodes : plate and cathode Thursday, 25 April 13

p-n Junctions (Semiconductor) Donor atoms have 5 valence electrons, create an N-type. Doped with semi-conductor Makes the crystal negative. (excess electrons) e.g. Ar, P Acceptor atoms have 3 valence electrons, create a P-type. Doped with semi conductor. Makes crystal positive (lack of electrons) e.g. Al, B, Ga NB : Semi conductors have 4 valence electrons When combined, P-N junction is created, makes a junction field. When charged at N-type, electrons on N-type crosses over the junction. When reversed, Junction field grow larger, not allow current to flow. Thursday, 25 April 13

Graph Shape of curve determined by transport of charge carriers through depletion layer. When p.d. is increased above cut in voltage, diode allows current to flow out, VI curve at this point is exponential. At very large reverse bias, reverse breakdown occurs that causes a large increase in current. The second region, at reverse biases more positive than the PIV , has only a very small reverse saturation current. Thursday, 25 April 13