Diode Theory Chapter 3

Copyright © The McGraw-Hill Companies, Inc., Permission required for reproduction or display Topics Covered in Chapter 3 Schematic Symbol Diodes, A Non-linear Device Calculating Bulk Resistance Diode Approximations Reading a Data Sheet Testing a Diode Sample Problems

Schematic Symbol Copyright © The McGraw-Hill Companies, Inc., Permission required for reproduction or display Anode Cathode

Linear Devices The relationship between the voltage across and the current flowing through a resistor is linear. As the voltage increases, the current increases proportionately. As the voltage decreases, the current decreases proportionately. Copyright © The McGraw-Hill Companies, Inc., Permission required for reproduction or display V = I x R

Diodes, A Non-Linear Device The relationship between the voltage across and the current flowing through a diode is non-linear. Copyright © The McGraw-Hill Companies, Inc., Permission required for reproduction or display

Diodes, A Non-Linear Device Copyright © The McGraw-Hill Companies, Inc., Permission required for reproduction or display

Diodes, A Non-Linear Device Copyright © The McGraw-Hill Companies, Inc., Permission required for reproduction or display

Silicon Diode V-I Curve Copyright © The McGraw-Hill Companies, Inc., Permission required for reproduction or display

Diode Current (mA) Diode Voltage (V) Knee Silicon Diode V-I Curve Copyright © The McGraw-Hill Companies, Inc., Permission required for reproduction or display

Diode Voltage (V) Diode Current (mA) Breakdown Silicon Diode V-I Curve Copyright © The McGraw-Hill Companies, Inc., Permission required for reproduction or display

Bulk Resistance The bulk resistance is comprised of the resistance of the P and N material. Bulk resistance is typically less than 1  When forward biased, after the knee voltage is met, diode current increases rapidly. Copyright © The McGraw-Hill Companies, Inc., Permission required for reproduction or display

Bulk Resistance Copyright © The McGraw-Hill Companies, Inc., Permission required for reproduction or display Diode Current (mA) V 1, I 1 V 2, I 2 Diode Voltage (V)

1 st Approximation (Ideal Diode) When Forward Biased –Diode behaves like a closed switch. When Reverse Biased –Diode behaves like an open switch. The bulk resistance and knee voltage are ignored. Copyright © The McGraw-Hill Companies, Inc., Permission required for reproduction or display

2 nd Approximation When Forward Biased –Diode behaves like a closed switch and the knee voltage is included. When Reverse Biased –Diode behaves like an open switch. The bulk resistance is ignored. Copyright © The McGraw-Hill Companies, Inc., Permission required for reproduction or display

3 rd Approximation When Forward Biased –Diode behaves like a closed switch. The knee voltage and bulk resistance are included. When Reverse Biased –Diode behaves like an open switch. The knee voltage and bulk resistance are included. Copyright © The McGraw-Hill Companies, Inc., Permission required for reproduction or display

Appropriate Use of Approximations 1 st Approximation –Troubleshooting –High Voltage Circuit Calculations 2 nd Approximation –Low Voltage Circuit Calculations 3 rd Approximation –Circuit Modeling Copyright © The McGraw-Hill Companies, Inc., Permission required for reproduction or display