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1. Identify the types of diodes.2. Discuss, illustrate and derive the related equations of various rectifier circuits.3. Discuss the block diagram of a power supply. You may illustrate it and the corresponding waveforms.4. State other applications of a diode. (Rectifier circuit is an application of diode)I. TYPES OF DIODELight Emitting Diode (LED): It is one of the most popular type of diodes and when this diode permits the transfer of electric current between the electrodes, light is produced.Avalanche Diode: This type of diode operates in the reverse bias, and used avalanche effect for its operation. The avalanche breakdown takes place across the entire PN junction, when the voltage drop is constant and is independent of current.Laser Diode: This type of diode is different from the LED type, as it produces coherent light. These diodes find their application in DVD and CD drives, laser pointers, etc.Schottky Diodes: these diodes are constructed differently from normal diodes, with metal to semiconductor contact. Schottky diodes are used in RF applications, rectifier applications and clamping diodes.Zener diode: This type of diode provides a stable reference voltage, thus is a very useful type and is used in vast quantities. In power supplies, these diodes are widely used to provide a reference voltage.Photodiode: Photodiodes are used to detect light and feature wide, transparent junctions. Generally, these diodes operate in reverse bias, wherein even small amounts of current flow, resulting from the light, can be detected with ease. Photodiodes can also be used to generate electricity, used as solar cells and even in photometry.Varicap Diode or Varactor Diode: This diode acts as a capacitor and capacitor plates are formed by the extent of conduction regions and the depletion region as the insulating dielectric. Rectifier Diode: These diodes are used to rectify alternating power inputs in power supplies. They can rectify current levels that range from an amp upwards.Small signal or Small current diode – These diodes assumes that the operating point is not affected because the signal is small.Transient voltage suppression diodes – This diode is used to protect the electronics that are sensitive against voltage spikes.Large signal diodes – The operating point in these diodes get affected as the signal is large.Gold doped diodes – These diodes use gold as the dopant and can operate at signal frequencies even if the forward voltage drop increases.Super barrier diodes – These are also called as the rectifier diodes. This diodes have the property of low reverse leakage current as that of normal p-n junction diode and low forward voltage drop as that of Schottky diode with surge handling ability.Point contact diodes – The construction of this diode is simpler and is used in analog applications and as a detector in radio receivers. This diode is built of n – type semiconductor and few conducting metals placed to be in contact with the semiconductor.Peltier diodes – This diode is used as heat engine and sensor for thermoelectric cooling.Gunn diode – This diode is made of materials like GaAs or InP that exhibit a negative differential resistance region.Crystal diode: This diode comprises of a thin sharpened metal wire which is pressed against the semiconducting crystal.Silicon controlled rectifier – As the name implies this diode can be controlled or triggered to the ON condition due to the application of small voltage.Vaccum diodes – This diode is two electrode vacuum tubes which can tolerate high inverse voltages.II. VARIOUS RECTIFIER CIRCUIT2.1 Single-Phase System2.1.1 Half-wave Rectifier (Center-tapped) – This is the simplest structure. Only one diode is placed at the secondary of the transformer. Using the definitions reported in the previous section, we get the following results: And, similarly, we can calculate the other parameters: The current in the secondary of the transformer can flow only when the diode conducts and therefore it is equal to the current in the load: The poor performance of this rectifier is also confirmed by the utilization of the transformer. It is clear that the inverse voltage seen by the diode in its blocking state is the negative half-wave of vS(t). Similarly, the current that flows across the diode is the same as flows in the load. For this topology, one has to choose diodes with: 2.1.2 Full-Wave Rectifier – In order to use both halves of the secondary AC voltage waveform, one can use two diodes and create a return path for the current by adding a tap at the centre of the secondary winding. This is the so-called centre-tapped rectifier. Using the definitions reported in the previous section and the symmetries, we get the following results: As it is a single-way topology, there is a direct current in both the secondary windings; these results in a low TUF (compared to the bridge solutions, see next section). TUF = 0.671 (or 0.572 TUF = according to some authors). (33) Even though this solution is much better than the previous one, there are some drawbacks. As can be seen, when a diode is conducting, the other, which is in the blocking state, sees the inverse voltage of both windings of the secondary. The PIV of the diodes is higher. From the diode current point of view, this topology is equivalent to two half-waves acting alternately. For this topology, one has to choose diodes with: 2.1.3 Full-wave Rectifier (Bridge) – The bridge structure is the best single-phase rectifier. At the cost of two more diodes, several advantages are obtained. This is a full-wave rectifier, but compared with the centre-tapped solution it uses a simpler transformer, with a single secondary and no additional taps. The rectification takes place by the conduction of couples of diodes. Diodes D1 and D4 are conducting during the positive half-wave of the voltage. Diode D2 and D3 are conducting during the negative half. This is a double-way topology. In each half-cycle the current flows in both directions in the secondary winding but always in the same direction in the load. There is no DC component in the winding and the core can be smaller than that for a centre-tapped rectifier with the same DC power rating. Since this is a full-wave topology, Eqs. (28) to (32) are still valid but the transformer utilization factor is different. A sinusoidal current flows in both the primary and secondary windings, therefore VAP = VAS. From the definition (14), using (26) and (28) and considering that iS (t) = iL(t) we get: Looking at the PIV of the diodes, VS is the highest voltage seen by each diode in its blocking state. Therefore the diodes must have III. BLOCK DIAGRAM OF POWER SUPPLYMany electronic circuits need a direct current (DC) voltage source, but what we commonly find are voltage sources of alternating current (AC).In order to achieve a direct current voltage source, the alternating current input must follow a conversion process like the one shown in the chart below.The chart shows the operation of a voltage power supply using a block diagram. It also shows the waveforms at the beginning (AC input), at the end (DC output) and between each of the blocks. Input signal which goes to the primary of the transformer is a sine wave and its amplitude depends on the country where we live (110/220 VAC or other). See the basic units of measurement in electronics. IV. STATE OTHER APPLICATIONS OF DIODEThe simplest semiconductor component, the diode, has an astonishing number of applications that are enabled by a number of practical and unique types of diodes that are vital in modern electronics.4.1 Application of Diode4.1.1 Rectifying a voltage, such as turning AC into DC voltages – The primary application of rectifiers is to derive DC power from an AC supply (AC to DC converter). Rectifiers are used inside the power supplies of virtually all electronic equipment. AC-DC power supplies may be broadly divided into linear power and switched-mode power supplies. In such power supplies, the rectifier will be in series following the transformer, and be followed by a smoothing filter and possibly a voltage regulator.4.1.2 Isolating signals from a supply – Electronic isolation is a means of preventing the transfer of direct current (dc) and unwanted alternating current (ac) between two parts of a system while still enabling signal and power transfer between those two parts.4.1.3 Voltage Reference – A voltage reference is an electronic device which produces a constant voltage regardless of the loading on the device, temperature changes, passage of time and power supply variations. 4.1.4 Mixing of Signals – The mixing of a number of audio signals is such a common thing to do that one would expect the Net to be riddled with articles on how and why signals are mixed. There are plenty of circuits that show how it can be done, but very little that explains the benefits or drawbacks of any particular scheme.4.1.5 Detection Signals – Detection theory or signal detection theory is a means to quantify the ability to discern between information-bearing patterns (called stimulus in living organisms, signal in machines) and random patterns that distract from the information (called noise, consisting of background stimuli and random activity of the detection machine and of the nervous system of the operator). In the field of electronics, the separation of such patterns from a disguising background is referred to as signal recovery. 4.1.6 Demodulation of Signals – The most common use for diodes is to remove the negative component of an AC signal so it can be worked with easier with electronics.4.1.7 Over-Voltage Protections – Diodes also function well as protection devices for sensitive electronic components. When used as voltage protection devices, the diodes are non-conducting under normal operating conditions but immediately short any high voltage spike to ground where it cannot harm an integrated circuit.4.1.8 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.References

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