An AC powered unregulated power supply usually uses a transformer to convert the voltage from the wall outlet (mains) to a different, nowadays usually lower, voltage. If it is used to produce DC, a rectifier is used to convert alternating voltage to a pulsating direct voltage, followed by a filter, comprising one or more capacitors, resistors, and sometimes inductors, to filter out (smooth) most of the pulsation. A small remaining unwanted alternating voltage component at mains or twice mains power frequency
(depending upon whether half- or full-wave rectification is used)—ripple—is unavoidably superimposed on the direct output voltage.
For purposes such as charging batteries the ripple is not a problem, and the simplest unregulated mains-powered DC power supply circuit consists of a transformer driving a single diode in series with a resistor.
Before the introduction of solid-state electronics, equipment used valves (vacuum tubes) which required high voltages; power supplies used step-up transformers, rectifiers, and filters to generate one or more direct voltages of some hundreds of volts, and a low alternating voltage for filaments. Only the most advanced equipment used expensive and bulky regulated power supplies.

TRANSFORMER
A transformer is a static electrical device that transfers energy by inductive coupling between its winding circuits. A varying current in the primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic flux through the secondary winding. This varying magnetic flux induces a varying electromotive force (EMF) or voltage in the secondary winding.
Transformers range in size from thumbnail-sized used in microphones to units weighing hundreds of tons interconnecting the power grid . A wide range of transformer designs are used in electronic and electric power applications. Transformers are essential for the transmission , distribution , and utilization of electrical energy .
In electronics, a center tap is a contact made to a point halfway along a winding of a transformer or inductor , or along the element of a resistor or a potentiometer . Taps are sometimes used on inductors for the coupling of signals, and may not necessarily be at the half-way point, but rather, closer to one end. A common application of this is in the Hartley oscillator . Inductors with taps also permit the transformation of the amplitude of alternating current (AC) voltages for the purpose of power conversion, in which case, they are referred to as autotransformers , since there is only one winding. An example of an autotransformer is an automobile ignition coil . Potentiometer tapping provides one or more connections along the device's element, along with the usual connections at each of the two ends of the element, and the slider connection. Potentiometer taps allow for circuit functions that would otherwise not be available with the usual construction of just the two end connections and one slider connection.
• In a rectifier , a center-tapped transformer and two diodes can form a full-wave rectifier that allows both half-cycles of the AC waveform to contribute to the direct current, making it smoother than a half-wave rectifier . This form of circuit saves on rectifier diodes compared to a diode bridge , but has poorer utilization of the transformer windings. Center-tapped two-diode rectifiers were a common feature of power supplies in vacuum tube equipment. Modern semiconductor diodes are low-cost and compact so usually a four-diode bridge is used (up to a few hundred watts total output) which produces the same quality of DC as the center-tapped configuration with a more compact and cheaper power transformer. Center-tapped configurations may still be used in high-current applications, such as large automotive battery chargers, where the extra transformer cost is offset by less costly rectifiers. Center-tapped transformers are also used for dual-voltage power supplies. When a center-tapped transformer is combined with a bridge (four diode) rectifier, it is possible to produce a positive and a

negative voltage with respect to a ground at the tap. Dual voltage supplies are important for all sorts of electronics equipment.
A full-wave rectifier using two diodes and a center tap transformer.
RECTIFIER
A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The process is known as rectification . Physically, rectifiers take a number of forms, including vacuum tube diodes , mercury-arc valves , copper and selenium oxide rectifiers, solid-state diodes, silicon-controlled rectifiers and other silicon-based semiconductor switches. Historically, even synchronous electromechanical switches and motors have been used. Early radio receivers, called crystal radios , used a " cat's whisker " of fine wire pressing on a crystal of galena (lead sulfide) to serve as a point-contact rectifier or "crystal detector".
Rectifiers have many uses, but are often found serving as components of DC power supplies and high-voltage direct current power transmission systems. Rectification may serve in roles other than to generate direct current for use as a source of power. As noted, detectors of radio signals serve as rectifiers. In gas heating systems flame rectification is used to detect presence of flame.
The simple process of rectification produces a type of DC characterized by pulsating voltages and currents (although still unidirectional). Depending upon the type of end-use, this type of DC current may then be further modified into the type of relatively constant voltage DC characteristically produced by such sources as batteries and solar cells .
A more complex circuitry device which performs the opposite function, converting DC to AC, is known as an inverter .
•
Single-phase rectifiers
• Half-wave rectification
• Full-wave rectification

A full-wave rectifier converts the whole of the input waveform to one of constant polarity
(positive or negative) at its output. Full-wave rectification converts both polarities of the input waveform to pulsating DC (direct current), and yields a higher average output voltage. Two diodes and a center tapped transformer , or four diodes in a bridge configuration and any AC source (including a transformer without center tap), are needed.
[3]
Single semiconductor diodes, double diodes with common cathode or common anode, and four-diode bridges, are manufactured as single components.
Bridge rectifier: a full-wave rectifier using 4 diodes. full-wave rectifier. Twice as many turns are required on the transformer For single-phase AC, if the transformer is center-tapped, then two diodes back-to-back (cathode-to-cathode or anode-to-anode, depending upon output polarity required) can form a secondary to obtain the same output voltage than for a bridge rectifier, but the power rating is unchanged.
Full-wave rectifier using a center tap transformer and 2 diodes.

FILTER CAPACITOR
Filter capacitors are capacitors used for filtering of undesirable frequencies. They are common in electrical and electronic equipment, and cover a number of applications, such as:
• Glitch removal on Direct current (DC) power rails
• Radio frequency interference (RFI) removal for signal or power lines entering or leaving equipment
• Capacitors used after a voltage regulator to further smooth dc power supplies
• Capacitors used in audio, intermediate frequency (IF) or radio frequency (RF) frequency filters (e.g. low pass, high pass, notch, etc.)
• Arc suppression , such as across the contact breaker or 'points' in a spark-ignition engine
Filter capacitors are not the same as reservoir capacitors , the tasks the two perform are different, albeit related
The simple capacitor filter is the most basic type of power supply filter. The application of the simple capacitor filter is very limited. It is sometimes used on extremely high-voltage, low-current power supplies for cathode-ray and similar electron tubes, which require very little load current from the supply. The capacitor filter is also used where the power-supply ripple frequency is not critical; this frequency can be relatively high. The capacitor (C1) shown in figure 4-15 is a simple filter connected across the output of the rectifier in parallel with the load.
Figure 4-15. - Full-wave rectifier with a capacitor filter.
When this filter is used, the RC charge time of the filter capacitor (C1) must be short and the RC discharge time must be long to eliminate ripple action. In other words, the capacitor must charge up fast, preferably with no discharge at all. Better filtering also results when the input frequency is high; therefore, the full-wave rectifier output is easier to filter than that of the half-wave rectifier because of its higher frequency.
For you to have a better understanding of the effect that filtering has on E avg
, a comparison of a rectifier circuit with a filter and one without a filter is illustrated in views A and B of figure 4-16. The output waveforms in figure 4-16 represent the unfiltered and filtered outputs of the half-wave rectifier circuit.

Current pulses flow through the load resistance (R
L
) each time a diode conducts. The dashed line indicates the average value of output voltage. For the half-wave rectifier, E avg
is less than half (or approximately 0.318) of the peak output voltage. This value is still much less than that of the applied voltage. With no capacitor connected across the output of the rectifier circuit, the waveform in view A has a large pulsating component (ripple) compared with the average or dc component. When a capacitor is connected across the output (view B), the average value of output voltage (E avg
) is increased due to the filtering action of capacitor C1.
Operation of the simple capacitor filter using a full-wave rectifier is basically the same as that discussed for the half-wave rectifier. Referring to figure 4-18, you should notice that because one of the diodes is always conducting on. either alternation, the filter capacitor charges and discharges during each half cycle. (Note that each diode conducts only for that portion of time when the peak secondary voltage is greater than the charge across the capacitor.)
Full-wave rectifier (with capacitor filter)
Another thing to keep in mind is that the ripple component (E
r
) of the output voltage is an ac voltage and the average output voltage (E avg
) is the dc component of the output. Since the filter capacitor offers a relatively low impedance to ac, the majority of the ac component flows through the filter capacitor.
The ac component is therefore bypassed (shunted) around the load resistance, and the entire dc component (or E avg
) flows through the load resistance. This statement can be clarified by using the formula for X
C
in a half-wave and full-wave rectifier. First, you must establish some values for the circuit.
Remember, also, that the load resistance is an important consideration. If load resistance is made small, the load current increases, and the average value of output voltage (E avg
) decreases. The RC discharge time constant is a direct function of the value of the load resistance; therefore, the rate of capacitor voltage discharge is a direct function of the current through the load. The greater the load current, the more rapid the discharge of the capacitor, and the lower the average value of output voltage. For this reason, the simple capacitive filter is seldom used with rectifier circuits that must supply a relatively large load current. Using the simple capacitive filter in conjunction with a full-wave or bridge rectifier provides improved filtering because the increased ripple frequency decreases the capacitive reactance of the filter capacitor.

A resistor is a passive two terminal electrical component that implements electrical resistor as a circuit element.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. This relationship is represented by Ohm's law. where I is the current through the conductor in units of amperes V is the potential difference measured across the conductor in units of volts and R is the resistance of the conductor in units of ohm .The ratio of the voltage applied across a resistor's terminals to the intensity of current in the circuit is called its resistance, and this can be assumed to be a constant (independent of the voltage) for ordinary resistors working within their ratings.
Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel-chrome). Resistors are also implemented within integrated circuits particularly analog devices, and can also be integrated into hybrid and printed circuits.
The electrical functionality of a resistor is specified by its resistance: common commercial resistors are manufactured over a range of more than nine orders of magnitude. When specifying that resistance in an electronic design, the required precision of the resistance may require attention to the manufacturing tolerance of the chosen resistor, according to its specific application. The temperature coefficient of the resistance may also be of concern in some precision applications. Practical resistors are also specified as having a maximum power rating which must exceed the anticipated power dissipation of that resistor in a particular circuit: this is mainly of concern in power electronics applications. Resistors with higher power ratings are physically larger and may require heat sinks. In a high-voltage circuit, attention must sometimes be paid to the rated maximum working voltage of the resistor.
Practical resistors have a series inductance and a small parallel capacitance; these specifications can be important in high-frequency applications. In a low-noise amplifier or pre-amp, the noise characteristics of a resistor may be an issue. The unwanted inductance, excess noise, and temperature coefficient are mainly dependent on the technology used in manufacturing the resistor. They are not normally specified individually for a particular family of resistors manufactured using a particular technology.
[1]
A family of discrete resistors is also characterized according to its form factor, that is, the size of the device and the position of its leads (or terminals) which is relevant in the practical manufacturing of circuits using them.

STANDARD COLOUR CODE
Color
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Gray
White
Gold
Silver
None
Significant figures
–
–
8
9
–
6
7
4
5
2
3
0
1
Multiplier
×10 0
×10 1
×10 2
×10 3
×10 4
×10 5
×10 6
×10 7
×10 8
×10 9
×10 -1
×10 -2
–
Tolerance
±1%
–
±2%
(±5%)
±0.5%
±0.1%
–
±0.25%
±5%
±10%
±20%
J
K
M
G 50
15
– 25
D 20
C 10
B 5
±0.05% (±10%) A 1
–
Temp. Coefficient
(ppm/K)
250
F 100
U
S
R
P
Q
Z
Z
M
K
–
–
–
–

A voltage regulator is designed to automatically maintain a constant voltage level. A voltage regulator may be a simple "feed-forward" design or may include negative feedback control loops . It may use an electromechanical mechanism , or electronic components. Depending on the design, it may be used to regulate one or more AC or DC voltages.
Electronic voltage regulators are found in devices such as computer power supplies where they stabilize the DC voltages used by the processor and other elements. In automobile alternators and central power station generator plants, voltage regulators control the output of the plant. In an electric power distribution system, voltage regulators may be installed at a substation or along distribution lines so that all customers receive steady voltage independent of how much power is drawn from the line.

: To make a 5V DC power supply and operate EX-OR gate with this dc power supply.
1.
Centre tap transformer(12-0-12)
2.
Two diodes (1N4007)
3.
Capacitor(1000µf,25V)
4.
Voltage regulator(7805)
5.
Two current limiting resistors
6.
Light emitting diodes
7.
Quad 2-input XOR GATE(7486)

XOR GATE
The XOR gate (sometimes EOR gate , or EXOR gate ) is a digital logic gate that implements an exclusive or ; that is, a true output (1) results if one, and only one, of the inputs to the gate is true (1). If both inputs are false (0) or both are true (1), a false output (0) results..Its behavior is summarized in the truth table shown on the right. A way to remember XOR is "one or the other but not both".
XOR represents the inequality function, i.e., the output is HIGH (1) if the inputs are not alike otherwise the output is LOW (0). XOR can also be viewed as addition modulo 2. As a result,
XOR gates are used to implement binary addition in computers. A half adder consists of an XOR gate and an AND gate .
There are two symbols for XOR gates: the 'distinctive' symbol and the 'rectangular' symbol. For more information see Logic Gate Symbols .
'Distinctive' XOR Symbol

'Rectangular' XOR Symbol
The XOR gate with inputs A and B implements the logical expressions: or
This device contains four independent gates each of which performs the logic exclusive-OR function
.

MUKESH SINGH(UE124036)
• NIKHIL CHHABRA(UE124039)
• NITESH HINGONIA(UE124041)
• KARAM CHAND(UE124024)