Zener Diode

ATOMS All matter is made of atoms; and all atoms are made of electrons, protons, and neutrons. COPPER ATOM: The copper atom has 29 electrons that orbit the nucleus in four shells. Categories of Materials. There are three categories of materials are used in electrons: conductors, semiconductors, and insulators. Conductors : are materials that readily allow current. They have a large number of free electrons. Most metals are good conductors i.e. Silver and copper. Semiconductor: The semiconductors in their ability to carry current because they have fewer electrons than do conductors. Insulator: Insulating materials are poor conductors of electric current. In fact, insulators are used to prevent current SILICON AND GERMANIUM ATOMS. Two types of semi conductive materials are silicon and germanium. Both the silicon and the germanium atoms have four valence electrons. These atoms differ in that silicon has 14 protons in its nucleus and germanium has 32. ZENER DIODE: Zener diodes are primarily used as voltage regulators that regulate or maintain a constant DC load voltage inspite of changes in the source voltage or load resistance. Zener breakdodwn.Two types of reverse breakdown in a zener diode are avalanche and zener. The avalanche breakdown also occurs in rectifier diodes at a sufficiently high reverse voltage. Zener breakdown: occurs in a zener diode at low reverse voltages. A zener diode is heavily doped to reduce the breakdown voltage. SEMI-CONDUCTOR: It is a material which has a resistance in between that of a conductor and an insulator. POTENTIAL BARRIER: A restraining force due to which further diffusion of majority carries is stopped from one side of junctions to other. The collector The emitter is heavily doped The base is lightly doped and is thin BIPOLAR

The bipolar junction transistor (BJT) is a current controlled device; that is the base current controls the amount of collector current. A bipolar transistor is like two pn-junction diodes connected back to back. Used both Negative and Positive charge carrier. Operation depends on two types of charge carriers hole and electros. TRANSISTOR Having only one type of current carrier either ( hole or electron). It operation depends on only one type of charge carriers either hole or electron. Transistor conducts through only one piece of semi-conductor material ( P or N ). Transistor connection Common emitter CE Common Base CB Common collector CC

Positive voltages VBE and VCE

VCB VBC

Positive currents

i i i

BE CB BC

and

i

CE

Signal input Base Emitter Base

FET ( Field effect Transistor: It is a voltage controlled device in which the voltage at the gate terminal controls the amount of current through the device. MOSFET. ( Metal oxide semiconductor Field Effect Transistor): It has much higher input impedance than JFET. Type: 1) 2)

Enhancement-type. Depletion-type.

Diode: A semi-conductor diode is just a PN junction. Since current flows only one way, the main application. Diode: There are tow terminals of the diode are the anode (A) and cathode (K). The anode is the p region and the cathode is the n region. When the anode is positive with respect to the cathode, the diode is forward-biased and current (IF) is from cathode to anode. The ideal diode Model: The simplest way to visualize diode operation is to think of it as a switch. When forward-biased, the diode ideally acts as closed (on) switch, and when reverse-biased, it acts as an open (off) switch, AMPLIFIERS: Amplification means increasing the amplitude of a desired ac signal voltage or current. The amplifier allows a small input signal to control a larger amount of power in the output circuit. CLIPPERFS: The half wave rectifier is basically a clipper that eliminates one of the alternations of an ac signal. There are two types of clippers: the series clipper and the shunt clipper. Each of these can be positive or negative. The series clipper contains a diode that is in series with the load. The shunt clipper, on the other hand, contains a diode that is in parallel with the load.

Clippers are classified as being either series clippers or shunt clippers. Shunt clipper” A clipper that has an output when the diode is reverse biased ( not conducting) VL = _____RL______X Vin RL + RS CLIPPER ALLICATIONS: Clippers are used in a wide variety of electronic systems. They are generally used to perform on of several functions: 1. Altering the shape of a waveform. 2. Circuit transient protection. 3. Detection. CLAMPERS: The clampers are basically used to restore or change the dc reference of an ac signal. CLAMPERS OPERATION. The clamper works on the basis of switching time constants. Negative clampers vs positive clampers. As was the case with clippers, the difference between the negative clamper and positive clamper is simply the direction of the diode. Full wave rectifiers. The full wave rectifier is the most commonly used type in dc power supplies. HALF WAVE RECTIFIERS: Because of their ability to conduct current in one direction and block current in the other direction, diodes are used in circuits called rectifiers that convert ac voltage into dc voltage. The difference between full wave and half wave rectification is that a full wave rectifier allows unidirectional current to the load during the entire input cycle and the half wave rectifier allows this only during one half of the cycle. Effect of the Turns Ratio on Full wave output voltage: If the turns ratio of the transformer is 1, the peak value of the rectified output voltage equals half the peak value of the primary input voltage. Integrated circuit. The most popular IC regulators have three terminals an input terminal, an ouput terminal and a reference ( or adjust) terminal. BJT ( Bipolar junction transisitors). The BJT is constructed with three doped semi-conductor regions separated by two pn junctions, The three regions are called emitter, base and collector.

The base emitter (BE) junction is forward- biased and the base-collector(BC) junction is reverse-biased. The is called forward reverse bias. These direct currents ( emitter, base, and collector ) are also related by two parameters: the dc alpha(aDC ) which is ratio IC/IE and the dc beta (BDC) The collector current is equal to aDC times the emitter current. IC = aDCIE BJT as an Amplifier: DC bias allows a transistor to operate as an amplifier. An amplifier with voltage-divider bias with capacitively coupled input signal. Vin and Vout are with respect to ground. BJT as a switch. The basic operation of a transistor as a switching device. The transistor as a linear amplifier. The second major application area is switching applications. When used as an electronic switch, a transistor normally is operated alternately in cutoff and saturation.

1. The number of binary digits that make up the word is the _word length. 2. A byte is a 8 binary digit world. 3. A counter having a state sequence that terminates is sometimes called a saturating_counter. 4. A _register is a group of devices that store digital data. 5. The hexadecimal digits are 0 to 9 and A to F 6. How many inputs can be supplied to a logic gate with a fan in factor of four Ans. is ( Four) 7. How many flip flop circuits are needed to divided by 16 ? Ans ( Four ) 8. The op-amp. Is used in ? Ans ( Shift registers). 9. A toggle operation is used? Ans ( with a flip flop ) 10. Which circuit is used for a clock generator? Ans ( A free running MV ) 11. Which logic gate is similar to the function of two series switches ? Ans (AND gate). 12. Which logic gate is similar to the function of two parallel switches ? Ans ( OR gate) 13. Which logic function has the output low only when both inputs are high ? Ans (NAND gate ). 14. The truth table given below is for Ans ( AND Gate ) Input put Out put A B Y 0 0 0 0 0 0 1 0 0 1 0 1 15. The following truth table is for ?Ans ( X-NOR ) Input put A 0 0 1 1

17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27.

Out put Y 1 0 0 1

A combination of AND function and 0 NOT function result 1 is Ans (NAND gate 0 ). 1 16. A half adder includes includes ? Ans ( A AND gatae with XOR gate.) The number of levels in a digital signal is ? Ans ( two ) Which of the following is not valid is binary system ? Ans. 0 X 1 = 1. A device that converts from decimal to binary numbered is called. Ans ( enconder ). Which converter has a binary input ? Ans ( D/A ). Which of the following changes analog voltage to binary date? Ans ( A/D ) A half adder has? Ans ( 2 input and 2 outputs ). In a positive edge triggered JK flip flop, also J and a low K produce the inactive state. A high J and high K mean that the output will toggle on the rising edge of the clock. A Schmitt trigger is a digital circuit that produces a Rectangular output regardless of the input waveform. With a JK master slave flip flop the master is clocked when the clock is Ans High A fetch cycle is the? Ans ( first part of the instruction cycle) The program counter, which is a part of the control unit, counts from 0000 to 1111. It sends to the memory the address of the next instruction. B