Chapter Three-Diodes - Copy.pptx - 1 Chapter 3 Diodes and...

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© Niwareeba Roland 1 Diodes and Applications Chapter 3
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© Niwareeba Roland 2 Chapter Objectives Use a diode in common applications Analyze the voltage-current ( V - I ) characteristic of a diode Explain how the three diode models differ Explain and analyze the operation of half-wave rectifiers Explain and analyze the operation of full-wave rectifiers Explain and analyze power supply filters and regulators Explain and analyze the operation of diode limiters and clampers Explain and analyze the operation of diode voltage multipliers Interpret and use diode datasheets Troubleshoot diodes and power supply circuits
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© Niwareeba Roland 3 The diode A diode is a two-terminal semiconductor device formed by two doped regions of silicon separated by a pn junction. It is the simplest and most fundamental nonlinear circuit element. Just like a resistor, a diode has two terminals; but unlike the resistor, which has a linear (straight-line) relationship between the current flowing through it and the voltage appearing across it, the diode has nonlinear i-v characteristic.
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© Niwareeba Roland 4 Biasing a diode Biasing refers to the use of a dc voltage to establish certain operating conditions for an electronic device. In relation to a diode, there are two bias conditions: forward and reverse. Either of these bias conditions is established by connecting a sufficient dc voltage of the proper polarity across the pn junction.
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© Niwareeba Roland 5 Forward bias Forward bias is the condition that allows current through the pn junction. Figure below shows a dc voltage source connected by conductive material (contacts and wire) across a diode in the direction to produce forward bias. The external bias voltage is designated V BIAS . The resistor, R, limits the current to a value that will not damage the diode.
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© Niwareeba Roland 6 Forward bias Notice that the negative side of V BIAS is connected to the n region of the diode and the positive side is connected to the p region. This is one requirement for forward bias. A second requirement is that the bias voltage must be greater than the barrier potential. Because like charges repel, the negative side of the bias-voltage source “pushes” the free electrons, which are the majority carriers in the n region, toward the pn junction. This flow of free electrons is called electron current. The negative side of the source also provides a continuous flow of electrons through the external connection (conductor) and into the n region as shown...
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© Niwareeba Roland 7 Forward bias A forward-biased diode showing the flow of majority carriers and the voltage due to the barrier potential across the depletion region.
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© Niwareeba Roland 8 Forward bias The bias-voltage source imparts sufficient energy to the free electrons for them to overcome the barrier potential of the depletion region and move through into the p region. Once in the p region, these conduction electrons have lost enough energy to immediately combine with holes in the valance band.
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