DIODES DIODES ENABLING OBJECTIVES 1 1 Describe the

DIODES

ENABLING OBJECTIVES 1. 1 Describe the construction methods for manufacturing PN junction diodes 1. 2 Explain in detail the electrical characteristics of the PN junction diode 1. 3 Explain the Voltage-Current (V-I) characteristic curve for semiconductor diodes. 1. 4 Explain forward and reverse semiconductor diode biasing. 1. 5 Identify the parts of a diode on both an actual device and the schematic symbol of a diode. 1. 6 List the basic application where diodes are utilized. 1. 7 Explain the operation of a diode when used as a rectifier. 3

ALLOYED PN JUNCTION The materials are heated until the indium pellet melts and partially fuses with the N-type material, forming a PN junction. 4

DIFFUSED JUNCTION The most widely used method of making semiconductor diodes is by diffusion. The operation occurs at a very high temperature and the gaseous doping atoms penetrate, or diffuse, into the exposed surfaces of the N-type material, resulting in a PN junction. 5

PN JUNCTION N-type material is the Cathode P-type material is the Anode Both the P-type and the N-type material are electrically neutral. 6

BARRIER VOLTAGE The combination of the majority carriers at the junction results in a barrier voltage. 7

EPOXY DIODE PACKAGE 8

METAL PACKAGE CUT AWAY 9

FORWARD BIAS Cathode Anode Majority carriers are forced toward the junction where they will combine. 10

FORWARD BIAS Cathode Current Flow - Anode + The forward voltage drop (Vf) is typically 0. 7 V for a silicon diode and 0. 3 V for a germanium diode. 11

FORWARD BIAS ED 1 = 0. 7 V - + ER 1 = E - 0. 7 V + I = ER 1 / R 1 12

FORWARD BIAS If E = 15 V, D 1 is silicon, and R 1 = 1 KΩ, what is the circuit current and the voltage across D 1 and R 1? 13

REVERSE BIAS Majority carriers are drawn away from the junction enlarging the depletion region. 14

REVERSE BIAS - + The maximum reverse bias voltage that the diode can withstand is it’s peak inverse voltage rating (PIV). 15

REVERSE BIAS ED 1 = E - + ER 1 = 0 V I = 0 A A theoretically perfect diode has no leakage current. In reality, a small leakage current flows. Germanium diodes exhibit a greater leakage current than silicon diodes. 16

FORWARD/REVERSE BIAS Reverse bias current is due to leakage. 17

TESTING DIODES 18

SILICON DIODE VI CURVE 19

TEMPERATURE EFFECTS 20

GERMANIUM vs. SILICON Germanium Low forward voltage drop Reverse leakage current Silicon Higher forward voltage drop Minimal reverse leakage current 21

HALF WAVE RECTIFIER 22

CONVENTIONAL FULL WAVE RECTIFIER 23

FULL WAVE BRIDGE RECTIFIER 24

FULL WAVE RECTIFIERS 25

ENABLING OBJECTIVES 1. 1 Describe the construction methods for manufacturing PN junction diodes 1. 2 Explain in detail the electrical characteristics of the PN junction diode 1. 3 Explain the Voltage-Current (V-I) characteristic curve for semiconductor diodes. 1. 4 Explain forward and reverse semiconductor diode biasing. 1. 5 Identify the parts of a diode on both an actual device and the schematic symbol of a diode. 1. 6 List the basic application where diodes are utilized. 1. 7 Explain the operation of a diode when used as a rectifier. 26