Diode Types & Applications PDF

Lecture # 13,14,15 Various types of special diodes are: Light-Emitting Diode. Zener diode, Voltage regulator LM7805IC. Schottky diode. 1. Light-Emitting Diode (LED): The LED is a two terminals and two layers semiconductor device. The LED works in forward bias. The function of LED to...

Lecture # 13,14,15 Various types of special diodes are: Light-Emitting Diode. Zener diode, Voltage regulator LM7805IC. Schottky diode. 1. Light-Emitting Diode (LED): The LED is a two terminals and two layers semiconductor device. The LED works in forward bias. The function of LED to convert light energy into electrical energy (current). When supply the voltage, electrons will recombine with holes, due to this recombination current flows in LED then LED emits the light. The V-I characteristic of Light-Emitting Diode (LED) is a similar characteristics of p-n junction diode.  A K P N K, L, M, N Dc supply hole Free electron  Extrinsic semiconductor P-TYPE N-TYPE Trivalent impurity Pentavalent impurity  LEDs can emit red, green, orange, yellow, and blue light. Applications: Decorative lamps. Television remote. Display devices. 2. Zener diode(voltage regulator): The first Zener diode was been invented by American Scientist Clerance Zener in 1956. The Zener diode has two terminals and two layers. The schematic symbol for a Zener diode is very similar to that of a silicon diode, but with bent edges on the bar. A Zener diode is used for voltage regulation. P N Zener dode  The Zener diode work in both directions. There are different voltage ratings of Zener diodes are available (1.8 to 200V). Another name of Zener diode is breakdown diode. A Zener diode is always connected in reverse. Applications of Zener diode are: 1. Voltage regulation. 2. Switching purpose. 3. Dc power supply. Types of break down diodes are: Zener break down Avalanche break down Condition of zener diode in Reverse bias: In revrse bias that the anode must be connected to the negative side of the voltage source and the cathode must be connected to the positive side. Reverse characteristic of zener diode Condition of zener diode in forward bias: In forward bias that the anode must be connected to the negative side of the voltage source and the cathode must be connected to the positive side. Forward characteristic of zener diode  The Zener diode has two states, namely; on and Off. On state: When reverse voltage across from a Zener diode the Vz is equal to or more than breakdown voltage Vz, the current increases very sharply. Under such condition, the Zener is said to be the “ON” State Suppose: If Vz=5v or > 5v Off state: When reverse voltage across from a Zener diode is less than Vz < break down voltage but greater than 0V, the Zener diode is in the “Off” state. Under such condition, the Zener diode can be represented by open switch. Suppose: If Vz 0v V-I characteristic of Zener diode in forward and reverse bias: Example : 7v On off  Voltage regulator LM7805 IC: The IC is an abbreviation of integrated circuit. The IC is a combination of resistors, capacitors, inductors and transistors. The LM7805 IC has three terminals (Input, ground or common and output). A Voltage Regulator is an electronic device that is used to automatically maintain a constant voltage. The LM78 type of series work forward bias while LM79 series in reverse bias. There are different voltage ratings of Ic’s available for fixed voltages LM7805, LM7806, LM7809 and LM7812.  For 5v of IC, Minimum and Maximum voltage is required 7.2V to 35V.  PIN 1-INPUT: The function of this pin is to give the input voltage. It should be in the range of 7.2V to 35V. We apply an unregulated voltage to this pin for regulation. PIN 2-GROUND: We connect the ground to this pin. For output and input, this pin is equally neutral (0V). PIN 3-OUTPUT: This pin is used to take the regulated output. It will be 5v(4.8v-5.2v).  How to identify the voltage regulator IC ? IC 7805 is a series of LM78XX voltage regulators. It’s a standard, from the name the last two digits 05 denotes the amount of voltage that it regulates. Hence a 7805 would regulate 5v and 7806 would be regulate 6V and so on. Different types of Ics are:  Advantages of Voltage regulator IC LM78XX: Low cost, easy to use, simple circuit. 78xx series ICs do not require additional components to provide a constant. Disadvantages of Voltage regulator IC LM78XX:  The voltage regulator IC can destroy, if the negative or reverse voltage is applied on its input.  The input voltage must always be higher than the output voltage by some minimum amount (typically 5 volts). Application of Voltage regulator IC LM78XX: The voltage IC LM78xx is used in all electronic components. Exp: Computer, TV, DC power supply etc. 3. Schottky diode: The Schottky diode is a two terminals semiconductor device. The Schottky diode was taken name after German Walter H. Schottky. In a normal p-n junction diode, when a p-type semiconductor is joined with an n-type semiconductor, a junction is formed between the P-type and N-type semiconductor. This junction is known as P-N junction. In Schottky diode, metals such as aluminum or platinum replace the P-type semiconductor. A K  In Schottky diode, the metal acts as the anode and n-type semiconductor acts as the cathode. When aluminum or platinum metal is joined with N-type semiconductor, a junction is formed between the metal and N-type semiconductor. This junction is known as a metal- semiconductor junction or M-S junction. Schottky diode is also known as Schottky barrier diode, surface barrier diode.  The Schottky diode works in forward bias. The Schottky diode works on low voltage (0.3v). Schottky diodes are widely used in radio frequency (RF) applications and can be used switch on and off. Working of Schottky diode in forward bias: If the positive terminal of the battery is connected to the metal and the negative terminal of the battery is connected to the n-type semiconductor, the Schottky diode is said to be forward biased. When a forward bias voltage(0.3v) is applied to the Schottky diode, many free electrons are generated in the n-type semiconductor and metal. If the applied voltage is greater than 0.3 volts, as a result, electric current starts flowing through the Schottky diode. Working of Schottky diode in reverse bias: If the negative terminal of the battery is connected to the metal and the positive terminal of the battery is connected to the n-type semiconductor, the Schottky diode is said to be reverse biased. When a reverse bias voltage is applied to the Schottky diode, the depletion width increases. As a result, the electric current stops flowing. However, a small leakage current flows due to the thermally excited electrons in the metal.  V-I characteristics of Schottky diode: The vertical line in the below figure represents the current flow in the Schottky diode and the horizontal line represents the voltage applied across the Schottky diode. The V-I characteristics of Schottky diode is almost like the P-N junction diode. 0.3 0.7