INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH SECOND SEMESTER ELECTRONICS Module-1 PN Junction Diode

INSTITUTE OF APPLIED TECHNOLOGY INTRODUCTION Semiconductor devices, made electronics physically very small, for example: Computers. certain types of medical diagnostic and treatment equipment. popular telecommunication devices. INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

INSTITUTE OF APPLIED TECHNOLOGY Definition Define the term Diode. Diode is a PN junction semiconductor device that allows current to flow in only one direction. How does the current flow in the Diode? The current flows when the Anode (A) is made positive with respect to the Cathode (K). INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

INSTITUTE OF APPLIED TECHNOLOGY Diode Construction Diode is created by doping a single piece of pure semiconductor so that half is N-type and the other half is P-type as shown below. It has two electrodes and hence the name diode. (di  two and ode  electrode). The electrode connected to the P-type is called Anode “A” and that connected to N-type is called Cathode “K” Anode (A) Cathode (K) N-TYPE Electrons + Diode Structure P-TYPE Holes INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

INSTITUTE OF APPLIED TECHNOLOGY Diode Symbol The symbol of diode is shown below. K Diode Symbol A In the symbol, the arrow points from anode (A) to cathode (K), this is the direction of current flow. The cathode (K) is marked with a silver color band as shown below. Typical Diode K INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

INSTITUTE OF APPLIED TECHNOLOGY Types of Diode Commonly diodes are made of Silicon (Si) or Germanium (Ge). According to the application they are classified into: Low power diodes. Light Emitting Diodes (LEDs). Zener diodes. Rectifier diodes. INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

INSTITUTE OF APPLIED TECHNOLOGY Diode Packing Diode is generally mounted in one of the three basic packages as shown below. The function of the package is to protect the diode from mechanical stress and environment The size of the package indicates the current rating (larger size means higher current rating). DO-5 DO-41 DO-8 Diode packing types INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

INSTITUTE OF APPLIED TECHNOLOGY Diode Identification In order to distinguish between diodes, each type is given a unique code so that it can be identified. There are two main semiconductor numbering systems in use: Pro-Electron System: originated and widely used in Europe. JEDEC System: widely used in North America. INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

Diode Identification Pro-Electron Coding System A Germanium First Letter Specifies Semiconductor Material Second Letter Specifies type of Diode A Germanium Low power or signal B Silicon P Light detector EXAMPLE: BZY74-C6V3 B = Si, Z = Zener diode, Y74 = Commercial or Industrial use, C = 5% of rating voltage. 6V3 = 6.3 Volt (Rating Voltage) Q (LED) Y Rectifier Z Zener (V- reference) INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

JEDEC Numbering or Coding System INSTITUTE OF APPLIED TECHNOLOGY Diode Identification JEDEC Numbering or Coding System First Number Second Letter Subsequent numbers 1 Diode N Semiconductor Serial number 2 Bipolar Transistor Example: This code “1N4001” means: 1  Diode, N  Semiconductor 4001  Serial number 3 FET 4 & 5 Photo Coupler INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

INSTITUTE OF APPLIED TECHNOLOGY Diode Operation Forward Biased: The diode is forward biased (FB) when the (A) is positive with respect to the (K). The diode in FB allows the current to flow from A to K as shown below + K DC A R IF Diode Operated in FB Direction INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

INSTITUTE OF APPLIED TECHNOLOGY Diode Operation Reverse Bias: The diode is reverse biased (RB) when the (A) is negative with respect to the (K). The diode in RB does not allow the current to flow as shown below. + K DC A R Diode Operated in RB Direction INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

Testing the Diode in FB Direction Testing in Forward Direction with an Ohmmeter: Connect the Red-lead to the (A) and connect the Black-lead to the (K) as shown below. A good diode must display low resistance (typically < 10) in FB. Testing the Diode in FB Direction IN 4001 K Ohmmeter A INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

Testing the Diode in RB Direction Testing in Reverse Direction with an Ohmmeter: Connect the Red-lead to the (K) and connect the Black-lead to the (A) as shown below. A good diode must display a very high resistance (> 1000 M) in RB. Testing the Diode in RB Direction IN 4001 K Ohmmeter A INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

Testing the Diode in FB Direction Testing in Forward Direction with a Digital Voltmeter: Connect the Red-lead to the (A) and connect the Black-lead to the (K) as shown below. For a diode in a good condition the reading will be in the range of  0.3V for Ge and  0.7V for Si. Testing the Diode in FB Direction IN 4001 K A Voltmeter Digital INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

Testing the Diode in RB Direction Testing in Reverse Direction with a Digital Voltmeter: Connect the Red-lead to the (K) and connect the Black-lead to the (A) as shown below. For a diode in a good condition the reading will be  1.5V for both Ge and Si (in some cases it shows OL). Testing the Diode in RB Direction IN 4001 K A Voltmeter Digital INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

INSTITUTE OF APPLIED TECHNOLOGY Testing the Diode When Testing with Analogue Voltmeter: If both bias conditions show low resistance, then the diode is shorted. If both bias conditions show very high resistance, then the diode is open circuit. When Testing with Digital Voltmeter: If in both cases the reading is 0V, then the PN junction is shorted, and if it is 1.5V then the PN junction is open. INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

INSTITUTE OF APPLIED TECHNOLOGY Diode Application The diode offers very little resistance to the current flow in the FB direction. It offers very high resistance to the current flow in RB. For this reason, the diodes are used in rectification. What is Rectification? It is the process of converting ac to pulsating dc. INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

AC Current Behavior The AC current reverses its direction with each alteration as shown below. I Positive half-cycle +ve +ve -ve -ve Negative half-cycle I Alteration of AC current between (+ve) and (-ve) INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

Half Wave Rectifier Circuit The half-wave rectifier circuit is constructed simply by connecting a diode between the secondary of a transformer and the load as shown below. Load Half Wave Rectifier Circuit IF AC Input A K INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

Operation of Half-Wave Rectifier INSTITUTE OF APPLIED TECHNOLOGY During the positive half-cycle, the diode turns ON and connects the positive half-cycle across the load (RL). During the negative half-cycle, the diode turns OFF (RB) as shown below. The lamp is ON during the +ve half cycle only. IF A K + Load AC Input Output Operation of Half-Wave Rectifier INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

INSTITUTE OF APPLIED TECHNOLOGY Half Wave Rectifier Output Voltage Only positive half-cycles of the AC input appear across the load, providing a pulsating DC voltage at the output as shown below. VS Secondary Voltage (VS) VRL Voltage across the Load Output of Half-Wave Rectifier Voltage INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH

INSTITUTE OF APPLIED TECHNOLOGY The End Of Module-1 INSTITUTE OF APPLIED TECHNOLOGY FUJAIRAH