Zener Diode as Voltage Regulators

Zener Diode as Voltage Regulators

The function of a regulator is to provide a constant output voltage to a load connected in parallel with it in spite of the ripples in the supply voltage or the variation in the load current and the zener diode will continue to regulate the voltage until the diodes current falls below the minimum I_Z(min) value in the reverse breakdown region. It permits current to flow in the forward direction as normal, but will also allow it to flow in the reverse direction when the voltage is above a certain value - the breakdown voltage known as the Zener voltage. The Zener diode specially made to have a reverse voltage breakdown at a specific voltage. Its characteristics are otherwise very similar to common diodes. In breakdown the voltage across the Zener diode is close to constant over a wide range of currents thus making it useful as a shunt voltage regulator.

The purpose of a voltage regulator is to maintain a constant voltage across a load regardless of variations in the applied input voltage and variations in the load current. A typical Zener diode shunt regulator is shown in Figure 3. The resistor is selected so that when the input voltage is at V_IN(min) and the load current is at I_L(max) that the current through the Zener diode is at least I_z(min). Then for all other combinations of input voltage and load current the Zener diode conducts the excess current thus maintaining a constant voltage across the load. The Zener conducts the least current when the load current is the highest and it conducts the most current when the load current is the lowest.

Fig 3: Zener diode shunt regulator

If there is no load resistance, shunt regulators can be used to dissipate total power through the series resistance and the Zener diode. Shunt regulators have an inherent current limiting advantage under load fault conditions because the series resistor limits excess current.    

                            

 A zener diode of break down voltage V_z is reverse connected to an input voltage source V_i across a load resistance R_L and a series resistor R_S. The voltage across the zener will remain steady at its break down voltage V_Z for all the values of zener current I_Z as long as the current remains in the break down region. Hence a regulated DC output voltage V₀ = V_Z is obtained across RL, whenever the input voltage remains within a minimum and maximum voltage.
             
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Implement Xnor Using Nand & Nor , Xor Using Nand & Nor

XNOR USING NAND ONLY

XNOR USING NOR ONLY

XOR USING NAND ONLY

XOR USING NOR ONLY

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V-I characteristics of p-n junction diode

V-I characteristics of p-n junction diode (~:http://gopalec201.blogspot.in/:~)

If we apply forward bias to the PN-junction diode, that means negative terminal is connected to the P-type material and the positive terminal is connected to the N-type material across the diode which has the effect of decreasing the width of the PN junction diode.

If we apply reverse bias to the PN-junction diode, that means positive terminal is connected to the P-type material and the negative terminal is connected to the N-type material across the diode which has the effect of increasing the width of the PN junction diode and no charge can flow across the junction

VI Characteristics of PN Junction Diode

Energy band diagram of n-type, p-type & pn junction diode

N-Type Band Structure The addition of donor impurities contributes electron energy levels high in the semiconductor band gap so that electrons can be easily excited into the conduction band. This shifts the effective Fermi levelto a point about halfway between the donor levels and the conduction band. Electrons can be elevated to the conduction band with the energy provided by an applied voltage and move through the material. The electrons are said to be the "majority carriers" for current flow in an n-type semiconductor.

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P-Type Band Structure The addition of acceptor impurities contributes hole levels low in the semiconductor band gap so that electrons can be easily excited from the valence band into these levels, leaving mobile holes in the valence band. This shifts the effective Fermi level to a point about halfway between the acceptor levels and the valence band. Electrons can be elevated from the valence band to the holes in the band gap with the energy provided by an applied voltage. Since electrons can be exchanged between the holes, the holes are said to be mobile. The holes are said to be the "majority carriers" for current flow in a p-type semiconductor.                               ~:gopalec201.blogspot.com:~

P-N Energy Bands

For a p-n junction at equilibrium, the Fermi levels match on the two sides of the junctions. Electrons and holes reach an equilibrium at the junction and form a depletion region. The upward direction in the diagram represents increasing electron energy. That implies that you would have to supply energy to get an electron to go up on the diagram, and supply energy to get a hole to go down.
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Cut off, Active and saturation regions of a Transistor

Cut off, Active and saturation  regions of a   transistor:

Transistor Biasing:-

                 The application of suitable dc voltages across the transistor terminals is called biasing. Each  junction of a transistor may be forward biased or reverse biased independently.These are following three different ways of biasing a transistor ,which is also known as modes of transistor operation.

Forward active:-

                        Emitter-Base junction is forward biased

                        Collector- base junction is reverse biased.

Saturation Region:-

                        

                    Emitter-Base junction  is forward biased

                    Collector- base junction is forward biased

In this mode transistor has a very large value of current. The transistor is operated in this mode, when it is used as a closed switch. 

Cut- off Region:-

                    Emitter-Base junction  is reverse biased

                    Collector- base junction is reverse biased

In this region both the junctions are Reverse Biased. In this mode transistor has zero current. The transistor is operated in this mode, when it is used as an open switch.

   Output characteristics of Common Emitter Transistor

    Modes of transistor action:

                   

S.no	Junction bias condition
1. 2. 3.	Mode	Emitter-base	Collector-base
	Forward-Active Saturation Cut-off	Forward Forward Reverse	Reverse Forward Reverse

Mass action law

MASS ACTION LAW:

This law states the relation between concentrations of minority and majority carriers at a constant temperature. It states that product of concentration of majority and minority carrier is constant at fixed temperature. According to the law

                                n * p = n_i² at constant temperature

• n_i² is the intrinsic concentration given by   and is constant at a temperature
• n is the concentration of electrons and p is the concentration of holes. So in p-type material, p is concentration of majority carriers and n is concentration of minority carriers. Similarly in n-type, n is concentration of majority carriers and p is concentration of minority carriers.

According to the law, if we increase the doping level of the material i.e. concentration of majority carriers, then concentration of minority carriers would decrease.

Frequency of output of full-wave rectifier

Frequency of output of full-wave rectifier

Frequency is measured by how frequently the period is completed in one second. The output signal completes a period twice as fast as the input frequency, as you can see in the diagram.

This is because the input wave is symmetrical, half positive and half negative. Making all the negative components into positive ones doubles the positive components. The positive component is only half of the original period. Thus the period is halved and the frequency is doubled.

Peak Inverse Voltage

Pick inverse voltage(PIV)

The Peak inverse voltage (PIV) equals the peak value of the input voltage, and the diode must be capable of withstanding this amount of repetition reverse voltage. For the diode in figure, the maximum value of reverse voltage, designated as PIV, occurs at peak of each positive alternation of the input voltage when the diode is forward biased.
Or simply ~  Peak Inverse Voltage (PIV) or Peak Reverse Voltage (PRV) refer to the maximum voltage a diode or other device can withstand in the reverse-biased direction before breakdown. Also may be called Reverse Breakdown Voltage.

Importance of PIV

Typically this is the maximum reverse polarity voltage that can be applied to a diode before it starts to break down and conduct current.  Diodes always have a reverse leakage current, although usually very small for rectifier diodes (100nA - 500uA would be typical), so the reverse voltage specification is the voltage at which the diode conducts a defined amount of current in the reverse direction.

Why NAND and NOR gate is called universal gates

Best answers :~

•  NAND and NOR gates are called universal gates because they can be used in place of all basic gates that AND ,OR and NOT.
  They can be used to implement any circuitory. We can use only one type of universal gate to implement any circuit.
  
  Gates are used as switches.
  They use a set of output signals to produce the desired output signal.

• All other gates/functions can be implemented by NOR or NAND gates. so they are called universal gates. In fact, in chips, entire logic maybe built using only NAND (or NOR) gates. eg: inverter-- nand with inputs shorted. and ------ nand followed by a inverter(using nand). or--------- giving inverted inputs to nand gate. If you delve deep into realms of VLSI you maybe able to understand the reason .Implementing with NAND is easier when considering power and area of the chip.

• NAND and NOR gates are called universal gates because they can be used in place of all basic gates that AND ,OR and NOT. They are inexpensive to make and they can be used to make any circuit thoughcan use only one type of universal gate to make any circuit. 
  Gates are mainly switches which can be used to decide the output of any input.They can be used to get desired results by givin inputs.

Varactor Diode

Varactor Diode & its application

Varactor

A varactor diode uses a p-n junction in reverse bias and has a structure such that the capacitance of the diode varies with the reverse voltage. A voltage controlled capacitance is useful for tuning applications. The capacitance is controlled by the method of doping in the depletion layer. Typical values are from tens to hundreds of picofarads.

Application of Varactor Diode

Following are the varactor diode applications:
1.  It is used in variable resonant tank LC circuit. Here C part is varied using varactor diode.
2.   AFC(Automatic Frequency Control) where in varactor diode is used to set LO signal.
3.   Varactor is used as frequency modulator.
4.  It is used as frequency multiplier in microwave receiver LO. 5.  It is used as RF phase shifter

Difference between Conductor, Semiconductor and Insulator

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Formation of N - type semiconductor

Formation of N - type semiconductor

An N - type semiconductor is formed when a small amount of pentavalent impurity is added to a pure Germenium or Silicon crystal. The addition of pentavalent impurity produces a large no. of free electrons in the host crystal.
To explain the formation of N - type semiconductor, let us introduce a pentavalent impurity atom into the lattice of pure silicon crystal. The pentavalent atom has 5 valance electrons, but only 4 form covalent bonds with the neighbouring atoms. The 5th electron finds no place in the covalent bonding so becomes free. Since an impurity atom provides one free electron, an enormous increase occurs in the no. of free electrons. The impure semiconductor so obtained is then called as N - type semiconductor where N represents negative charge on an electron. Thus the majority carrier in N - type semiconductor are free electrons. Holes are also present in the N - type semiconductor. These are thermally generated and since they are relatively few, they are called minority carrier.
The pentavalent impurity atom are called donour because each donate a free electron to the host crystal.

Formation of P - type semiconductor

Formation of P-type semiconductor

A P - type semiconductor is formed when a small amount of trivalent impurity is added to pure Germenium or silicon atom crystal. The addition of trivalent impurity produces a large no. of holes tothe host crystals. To explain the formation of P - type semiconductor, let us introduce a trivalent impurity into the lattice of a pure silicon crystal. The trivalent atom has 3 valance electrons and form covalent bonds with neighbouring atoms. The 4th bond is incomplete . the trivalent atom then attracts an electron from an adjacent atom there by completing the 4th bond and forming a hole in the adjacent atom. Since a trivalent impurity atom provides 1 hole, an enormous increase occurs in the number of holes. The impure crystals so obtained is called P - type

semiconductor where P represents the positive charge on hole. Thus the majority carrier in a P - type semiconductor are holes. Free electrons are also present in the P - type semiconductor. These are thermally generated and since they relatively few, they are called minority carriers. The trivalent impurity atoms are called acceptors because each accepts an electron when the atom is introduced into the host crystal.