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B6 - Section B6 Rectification Using Semiconductor Diodes...

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Section B6: Rectification Using Semiconductor Diodes Practically, we live in an ac world. However, many times a dc signal is required and we have to have a way to convert between ac and dc. This requires restricting the original ac signal that may alternate between positive and negative values to one that has values only on one side of the zero reference. The process of this conversion is called rectification and may be classified as either half-wave rectification or full-wave rectification. Half-Wave Rectification The simplest form of half-wave rectification is shown in Figure 3.30 in your text and is reproduced below in a more generic form. Part (a) of this modified figure corresponds to a simple two resistor circuit, where the relationship between the input and output voltages is defined by voltage division. The circuit in part (b) actually illustrates the process of half-wave rectification. The rectifier uses the ideal diode current characteristics ; i.e., current flows when the diode is forward biased and no current flows when the diode is reverse biased. If we further assume that we’re dealing with an ideal diode (with V on =0.7V), there is a simple 0.7 V drop across the diode in the forward bias region (that accounts for the turn-on voltage of a silicon diode). Using all this information, there are two distinct expressions for v o – a modified voltage divider relationship for forward bias, and a constant zero for reverse bias.
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To keep the numbers straightforward in the example of Figure 3.30 in your text, a 100 V ac input is assumed with 90 V dropped across the load resistor due to the voltage divider (and by considering the 0.7 V drop across the diode as negligible). This figure and discussion are quite good for illustration purposes, but keep in mind that sometimes the 0.7 V may not be negligible!
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