McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Electronics Principles & Applications Seventh Edition Chapter 3 Diodes (student version) Charles A. Schuler McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. The PN Junction Characteristic Curves of Diodes Diode Lead Identification Diode Types and Applications INTRODUCTION

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Dear Student: This presentation is arranged in segments. Each segment is preceded by a Concept Preview slide and is followed by a Concept Review slide. When you reach a Concept Review slide, you can return to the beginning of that segment by clicking on the Repeat Segment button. This will allow you to view that segment again, if you want to.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Concept Preview Diodes have both P-regions and N-regions. The boundaries are called junctions. The P-region is the anode side. The N-region is the cathode side. There are three possible bias conditions: zero, forward, and reverse. Zero bias is accompanied by a depletion region. Forward bias can collapse the depletion region. Reverse bias enhances the depletion region. Bias determines if diodes will be off or on.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. P The P-side of a junction diode is doped with acceptor atoms. N The N-side of a junction diode is doped with donor atoms. Schematic Symbol Cathode Anode junction A silicon crystal

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Zero Bias Depletion region The electrons near the junction cross over and fill the holes near the junction. Having no carriers, the depletion region is an insulator.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Forward Bias The carriers move toward the junction and collapse the depletion region. The diode is on.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Reverse Bias The carriers move away from the junction. The depletion region is reestablished and the diode is off.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Concept Review Diodes have both P-regions and N-regions. The boundaries are called junctions. The P-region is the anode side. The N-region is the cathode side. There are three possible bias conditions: zero, forward, and reverse. Zero bias is accompanied by a depletion region. Forward bias can collapse the depletion region. Reverse bias enhances the depletion region. Bias determines if diodes will be off or on. Repeat Segment

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Concept Preview The volt-ampere graph for a resistor is a straight line (a resistor is a linear device). The volt-ampere graph for a diode is non-linear. The knee voltage for a silicon diode is approximately 0.7 volts. This is the voltage required to collapse the depletion region. Excess reverse bias will result in diode breakdown. The cathode end might be marked with a band. Diodes can be tested with an ohmmeter.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. mA Volts 10 ohms 5 ohms 20 ohms Resistor volt-ampere characteristic curves

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Forward current in mA Forward bias in volts Silicon diode volt-ampere characteristic curve knee

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Linearity The volt-ampere characteristic curve for a resistor is a straight line (linear). A diode has a non-linear characteristic curve. The barrier potential produces a knee in the diode curve. The knee voltage is approximately 0.6 to 0.7 volts for silicon diodes.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Forward current in mA Forward bias in volts The effect of temperature -50 o C 25 o C 100 o C

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved Reverse bias in Volts Reverse current in mA Silicon diode reverse bias characteristic curve breakdown

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Cathode lead Anode lead

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Anode lead 0 V mA Cathode lead The diode is forward biased by the ohmmeter. 

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Cathode lead Anode lead 0 The diode is reverse biased by the ohmmeter. V mA 

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Silicon diode ohmmeter testing Low resistance in both directions: the diode is shorted. High resistance in both directions: the diode is open. Relatively low resistance in the reverse direction: the diode is leaky. The ratio of reverse resistance to forward resistance is > 1000: the diode is good.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Diode quiz At zero bias, diodes show a depletion region which acts as an________. insulator The depletion region is collapsed by applying _________ bias. forward The depletion region is made wider by applying ________ bias. reverse A forward-biased diode has its anode________ with respect to its cathode. positive Diode forward voltage drop decreases as temperature ________. increases

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Concept Review The volt-ampere graph for a resistor is a straight line (a resistor is a linear device). The volt-ampere graph for a diode is non-linear. The knee voltage for a silicon diode is approximately 0.7 volts. This is the voltage required to collapse the depletion region. Excess reverse bias will result in diode breakdown. The cathode end might be marked with a band. Diodes can be tested with an ohmmeter. Repeat Segment

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Concept Preview Zener diodes have a relatively low breakdown voltage and are often used as voltage regulators. Diode clippers limit signal amplitude. Diode clamps produce a dc signal component. Diodes can be used to suppress inductive kick. Optocouplers combine light emitting diodes and photodiodes. Fiber optic cables carry light signals. Varicap diodes are used to tune electronic circuits.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved Reverse bias in Volts Reverse current in mA A zener diode is designed to break down and conduct backwards at lower voltages.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved Reverse bias in Volts Reverse current in mA I V V The voltage across a conducting zener is relatively constant.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Unregulated Supply Load The load is in parallel with the zener and will see a relatively constant voltage as long as the zener is conducting. Using a zener diode as a voltage regulator

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. V IN V OUT When V IN < 1.2 V PP The diodes do not conduct. This circuit is called a clipper or limiter. V OUT is not clipped

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. V IN V OUT When V IN > 1.2 V PP V V V OUT is clipped The diodes conduct.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. V IN V OUT When V IN > 1.2 V PP This circuit is called a clamp or dc restorer. 0.6 V V OUT is clamped. dc C is charged. C 2 V OUT(dc) = V PP V

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. The inductive kick can cause damage. CEMF

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. The coil discharges through the diode and there is no arc. Transient suppression diodes can be used with inductive loads. CEMF

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. LED As the electrons cross the junction, they lose energy in the form of photons.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Power supply VSVS RSRS The typical voltage drop for most LEDs is from 1.5 to 2.5 V. LED I S = V S - V D RSRS LED circuit VDVD

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Power supply VSVS RSRS Photodiodes are reverse biased and conduct in the presence of light. Photodiode

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Input Output Input Output Optocoupler

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Step-index multimode fiber Input pulse Output pulse The combined shorter and longer path lengths act to stretch the output pulse.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Step-index multimode fiber Input Output Due to pulse stretching, high speed data transmission is not possible.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Input Output Single mode fiber A single path means no pulse stretching and high speed data transmission is possible.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. L C ZERO BIAS C is maximum and f R is minimum. Tuning diode

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. L C REVERSE BIAS C is less and f R increases. Tuning diode

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. L C MAX. REVERSE BIAS C is minimum and f R is maximum. Tuning diode

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Diode applications quiz A circuit used to control the amplitude of a signal is the ________. clipper A circuit used to add a dc component to a signal is the ________. clamp A device containing an LED and a photo- diode is the ________. optocoupler A tuning diode shows less capacitance as reverse bias ________. increases The device that is often used to regulate voltage is the ________ diode. zener

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Concept Review Zener diodes have a relatively low breakdown voltage and are often used as voltage regulators. Diode clippers limit signal amplitude. Diode clamps produce a dc signal component. Diodes can be used to suppress inductive kick. Optocouplers combine light emitting diodes and photodiodes. Fiber optic cables carry light signals. Varicap diodes are used to tune electronic circuits. Repeat Segment

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. REVIEW The PN Junction Characteristic Curves of Diodes Diode Lead Identification Diode Types and Applications