DIODE PDF FILE
Small-Signal Diodes. Diode: a semiconductor device, which conduct the current in one direction only. Two terminals: anode and cathode. When the positive. P/ Lec5, P1. Diodes and Transistors. Diodes. • What do we use diodes for ? protect circuits by limiting the voltage (clipping and clamping) turn AC into DC. Introduction to Diodes. Lecture notes: page to Sedra & Smith (6th Ed): Sec. 3.* and Sedra & Smith (5th Ed): Sec. * and Sec.
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PDF | Electronic devices are components for controlling the flow of electrical currents for Prominent examples include diodes and transistors. Understand the basic structure of semiconductors and how they conduct current. Describe the characteristics and biasing of a pn junction diode. Describe the. A diode is a dispositive made of a semiconductor material, which has two terminals or elec- trodes (di-ode), that act like an on-off switch. When the diode is “on”.
A diode's I—V characteristic can be approximated by four regions of operation: At very large reverse bias, beyond the peak inverse voltage or PIV, a process called reverse breakdown occurs that causes a large increase in current i. The avalanche diode is deliberately designed for use in that manner.
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In the Zener diode , the concept of PIV is not applicable. A Zener diode contains a heavily doped p—n junction allowing electrons to tunnel from the valence band of the p-type material to the conduction band of the n-type material, such that the reverse voltage is "clamped" to a known value called the Zener voltage , and avalanche does not occur. Both devices, however, do have a limit to the maximum current and power they can withstand in the clamped reverse-voltage region.
Also, following the end of forward conduction in any diode, there is reverse current for a short time. The device does not attain its full blocking capability until the reverse current ceases.
Different Types of Diodes
For a bias less than the PIV, the reverse current is very small. However, this is temperature dependent, and at sufficiently high temperatures, a substantial amount of reverse current can be observed mA or more.
There is also a tiny surface leakage current caused by electrons simply going around the diode as though it were an imperfect insulator. With a small forward bias, where only a small forward current is conducted, the current—voltage curve is exponential in accordance with the ideal diode equation.
There is a definite forward voltage at which the diode starts to conduct significantly. This is called the knee voltage or cut-in voltage and is equal to the barrier potential of the p-n junction.
This is a feature of the exponential curve, and appears sharper on a current scale more compressed than in the diagram shown here. At larger forward currents the current-voltage curve starts to be dominated by the ohmic resistance of the bulk semiconductor. At this point, load current IL is maximum and this is full load condition. Circuit in Figure 7 a will limit the forward voltage to VZ while in the negative cycle, the zener will act as a forward biased diode and limit the negative voltage to 0.
Circuit in Figure 7 b will act in the opposite manner to the circuit in a. Back to back zener diodes as in Figure 7 c will limit both peaks to 0. In the negative cycle, D2 acts like a forward biased diode while D1 acts like zener diode so the peak will be limited to 0. Diodes designed to be used as voltage controlled capacitors are called varactors.
They always work in reverse bias. The depletion region acts as dielectric and p and n-types act like capacitor plates.
Figure 8 Varactor 3. This decreases the capacitance.
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As the reverse bias decreases, the depletion region becomes narrow and decreases the plate separation d. This increases the capacitance. When the LED is forward biased, electrons cross the pn junction and recombines with the holes in the p-type.
When these high energy electrons recombine with holes, they release energy in the form of photons. Kido, J. C , 1 , Shirota, K. Okumoto, H. Inada, Synth. Zhou, J. Blochwitz, M. Pfeiffer, A. Nollau, T. Fritz, K.
Leo, Adv. Era, C.
Saito, Chem. Hosokawa, H. Higashi, H. Nakamura, T. Kusumoto, Appl, Phys. Adachi, M. Baldo, S. Forrest, M.A p—n junction diode is made of a crystal of semiconductor , usually silicon, but germanium and gallium arsenide are also used. To attain this performance they are designed in a different way to compare with normal diodes having a metal to semiconductor contact. Automotive alternators are a common example, where the diode, which rectifies the AC into dc, provides better performance than the commutator or earlier, dynamo.
Sometimes the abbreviation CR for crystal rectifier is used. At the time of their invention, asymmetrical conduction devices were known as rectifiers. A negative temperature coefficient means the zener voltage will decrease with increase in temperature or increase with decrease in temperature. Diodes designed to be used as voltage controlled capacitors are called varactors.
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The free electrons in the conduction band releases energy in the form of light before they recombine with holes in the valence band. Reverse breakdown is lower than silicon rectifier diodes 3V to 10V. These diodes can come as small signal types for use in RF radio frequency , or other low current applications which may be called as signal diodes.