1.Semiconductor diode. It is used in microwave applications

1.Semiconductor diodes are widely used throughout all areas of the electronics industry from electronics design through to production and repair. The semiconductor diode is very versatile, and there are very many variants and different types of diode that enable all the variety of different applications to be met.• Backward diode: This type of diode is sometimes also called the back diode. Although not widely used, it is a form of PN junction diode that is very similar to the tunnel diode in its operation. It finds a few specialist applications where its particular properties can be used.• BARITT diode: This form of diode gains its name from the words Barrier Injection Transit Time diode. It is used in microwave applications and bears many similarities to the more widely used IMPATT diode.• Gunn Diode: Although not a diode in the form of a PN junction, this type of diode is a semiconductor device that has two terminals. It is generally used for generating microwave signals.• Laser diode: This type of diode is not the same as the ordinary light emitting diode because it produces coherent light. Laser diodes are widely used in many applications from DVD and CD drives to laser light pointers for presentations. Although laser diodes are much cheaper than other forms of laser generator, they are considerably more expensive than LEDs. They also have a limited life. • Light emitting diodes: The light emitting diode or LED is one of the most popular types of diode. When forward biased with current flowing through the junction, light is produced. The diodes use component semiconductors, and can produce a variety of colours, although the original colour was red. There are also very many new LED developments that are changing the way displays can be used and manufactured. High output LEDs and OLEDs are two examples.• Photodiode: The photo-diode is used for detecting light. It is found that when light strikes a PN junction it can create electrons and holes. Typically photo-diodes are operated under reverse bias conditions where even small amounts of current flow resulting from the light can be easily detected. Photo-diodes can also be used to generate electricity. For some applications, PIN diodes work very well as photodetectors.• PIN diode: This type of diode is typified by its construction. It has the standard P type and N-type areas, but between them there is an area of Intrinsic semiconductor which has no doping. The area of the intrinsic semiconductor has the effect of increasing the area of the depletion region which can be useful for switching applications as well as for use in photodiodes, etc.• PN Junction: The standard PN junction may be thought of as the normal or standard type of diode in use today. These diodes can come as small signal types for use in radio frequency, or other low current  applications which may be termed as can be varied by changing the bias signal  diodes.  Other  types  may  be on  the  diode  as  this  will  vary  the intended  for  high  current  and  high width of the depletion region which voltage applications and are will accordingly change the normally termed rectifier diodes. capacitance. • Schottky diodes: This type of diode •  Zener diode:  The Zener diode is a has  a  lower  forward  voltage  drop very  useful  type  of  diode  as  it than  ordinary  silicon  PN  junction provides a stable reference voltage. diodes. At low currents the drop may As  a  result  it  is  used  in  vast be somewhere between 0.15 and 0.4 quantities.  It  is  run  under  reverse volts as opposed to 0.6 volts for a bias conditions and it is found that silicon   diode.   To   achieve   this when a certain voltage is reached it performance they are constructed in breaks down. If the current is limited a  different  way  to  normal  diodes through a resistor, it enables a stable having  a  metal  to  semiconductor voltage to be produced. This type of contact.  They  are  widely  used  as diode  is  therefore  widely  used  to clamping diodes, in RF applications, provide a reference voltage in power and also for rectifier applications. supplies.   Two   types   of   reverse• Step recovery  diode: A  form  of breakdown  are  apparent  in  these microwave diode used for generating diodes: Zener breakdown and Impact and  shaping  pulses  at  very  high Ionisation. However the name Zener frequencies. These diodes rely on a diode is used for the reference diodes very fast turn off characteristic of the regardless of the form of breakdown diode for their operation. that is employed. • Tunnel diode:  Although not widely • used today,  the tunnel diode was 2. used for   microwave applications where its performance exceeded that •  Half Wave Rectifier circuit: In half• of other devices of the day. wave rectification, when  a.c supply Varactor diode or varicap is applied at the input, only positive diode:  This type of diode is used in half  cycle  appears  across  the  load many radio frequency (RF) whereas  the  negative  half  cycle  is applications. The diode has a reverse suppressed. In a single phase supply, bias placed upon it  and this varies it requires a single diode while in a the  width  of  the  depletion  layer three phase supply it requires three according  to  the  voltage  placed diodes.  It  is  not  efficient  because across the diode. In this only  half  of  the  input  waveforms configuration the varactor or varicap reaches  the  output.  To  reduce  the diode acts like a capacitor with the ripples or to eliminate the harmonics depletion region being the insulating of the AC frequency from the output, dielectric  and  the  capacitor  plates more filtering is needed in half wave formed   by   the   extent   of   the rectifier circuit. conduction regions. The capacitance  Average voltage, Vaverage =Vm/? | Average Current, Iaverage =Im/? Rms Voltage, Vrms =Vm/2 | Rms Current, Irms =Im/2 • Full Wave Rectifier circuits: In full wave rectification, during both the half cycles when a.c. supply is applied to the input, current flows through the load in the samedirection. Full wave rectifiercircuit yields a higher average output voltage by changing the both polarities of the input waveform to pulsating DC. This type of rectification can be achieved by using at least two crystal diodes, conducting current alternatively. During positive as well as the negative half-cycle of the input AC the following two circuits namely centre tap full wave rectifier and full wave bridge rectifier is employed to obtain the same direction of flow of current in the load resistor. Average voltage, Vaverage =2Vm/? | Average  Current, Iaverage =2Im/? RMS Voltage, Vrms =Vm/?2 |    RMS Current, Irms =Im/?2 • Full wave center tap rectifier: Centre tap rectifier circuit employs a transformer with secondary winding tapped at the centre point. Two diodes are connected in the circuit so that each one of them uses one-half cycle of the input AC voltage. For rectification, one diode utilises the ac voltage appearing across the upper half of secondary winding while other diode uses the lower half of the secondary winding. The output and efficiency of this circuit are high because AC supply delivers power during both the halves. • Full Wave Bridge Rectifier: Bridge rectifier circuit is one of the efficient forms of full wave rectifier that utilises four diodes in a bridge topology. In place of centre tap transformer, in this case, an ordinary transformer is used. The AC supply to be rectified is applied to the diagonally opposite ends of the bridge and the load resistor is connected across the remaining two diagonally opposite ends of the bridge.3.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. CENTER TAP TRANSFORMERIn 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.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.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 engineFilter capacitors are not the same as reservoir capacitors, the tasks the two perform are different, albeit relatedA 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 asnickel-chrome). Resistors are also implemented within integrated circuits particularly analog devices, and can also be integrated into hybrid and printed circuits.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. 4.• Clamp: Also called a “dc restorer” in Sedra & Smith”. When a signal drives an open-ended capacitor the average voltage level on the output terminal of the capacitor is determined by the initial charge on that terminal and may therefore be quite unpredictable. Thus it is necessary to connect the output to ground or some other reference voltage via a large resistor. This action drains any excess charge and results in an average or DC output voltage of zero.• Clippers/Limiters: “A diode clipping circuit can be used to limit the voltage swing of a signal. Figure Ö shows a diode circuit that clips both the positive and negative voltage swings to references voltages.”• Power Conversion: One significant application of diodes is to convert AC power to DC power. A single diode or four diodes can be used to transform 110V household power to DC by forming a half-way (single diodes) or a full-wave (four diodes) rectifier. A diode does this by allowing only half of the AC waveform to travel through it. When this voltage pulse is used to charge a capacitor, the output voltage appears to be a steady DC voltage with a small voltage ripple.Using a full wave rectifier makes this process even more efficient by routing the AC pulses so both the positive and negative halves of the input sine wave are seen as only positive pulses, effectively doubling the frequency of the input pulses to the capacitor which helps keep it charged and deliver a more stable voltage.Diodes and capacitors can also be used to create a number of types of voltage multipliers to take a small AC voltage and multiply it to create very high voltage outputs. Both AC and DC outputs are possible using the right configuration of capacitors and diodes.• Demodulation of Signals: Diodes also function well as protection devices for sensitive electronic components. When used as voltage protection devices, the diodes arenon-conducting under normal operating conditions but immediately short any high voltage spike to ground where it cannot harm an integrated circuit. Specialized diodes called transient voltage suppressors are designed specifically for over-voltage protection and can handle very large power spikes for short time periods, typical characteristics of a voltage spike or electric shock, which would normally damage components and shorten the life of an electronic product.• Current Steering: The basic application of diodes is to steer current and make sure it only flows in the proper direction. One area where the current steering capability of diodes is used to good effect is in switching from power from a power supply to running from a battery. When a device is plugged in and charging, for example, a cell phone or uninterruptible power supply, the device should be drawing power only from the external power supply and not the battery and while the device is plugged in the battery should be drawing power and recharging. As soon as the power source is removed, the battery should power the device so no interruption in noticed by the user.• Diode Logic”To the left (above) you see a basic Diode Logic OR gate. We’ll assume that a logic 1 is represented by +5 volts, and a logic 0 is represented by ground, or zero volts. In this figure, if both inputs are left unconnected or are both at logic 0, output Z will also be held at zero volts by the resistor, and will thus be a logic 0 as well. However, if either input is raised to +5 volts, its diode will become forward biased and will therefore conduct. This in turn will force the output up to logic 1. If both inputs are logic 1, the output will still be logic 1. Hence, this gate correctly performs a logical OR function. “To the right (above) is the equivalent AND gate. We use the same logic levels, but the diodes are reversed and the resistor is set to pull the output voltage up to a logic 1 state. For this example, +V = +5 volts, although other voltages can just as easily be used. Now, if both inputs are unconnected or if they are both at logic 1, output Z will be at logic 1. If either input is grounded (logic 0), that diode will conduct and will pull the output down to logic 0 as well. Both inputs must be logic 1 in order for the output to be logic 1, so this circuit performs the logical AND function.”


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