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.
             
                                                                                      ~:http://gopalec201.blogspot.in/:~

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

                                                                   ~:http://gopalec201.blogspot.in/:~

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.