EECE312_Ch_02_Semic - Chapter 2: Semiconductors Devices and...

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Unformatted text preview: Chapter 2: Semiconductors Devices and circuits EECE312 Electronics Dr. Walid Kamali Fall 2007 Outline Intro to Electronics Engineering Rectifiers and Power Supplies The pn junction Diode BJT Operation Field Effect Transistors (a) diode circuit symbol; (b) i v characteristic; (c) equivalent circuit in the reverse direction; (d) equivalent circuit in the forward direction. The Ideal Diode The two modes of operation of ideal diodes and the use of an external circuit to limit the forward current (a) and the reverse voltage (b) . Operational modes Half-wave Rectifier circuit Input waveform. p L dc dc L p T T T L p T L dc V R I V R V dt dt t R V T dt t i T I = = = + = = 2 2 ) sin( 1 ) ( 1 Ideal Rectifying Diode Circuit Transfer Characteristic Conduction angle Application: Battery Charger Half-wave rectifier . (b) Equivalent circuit of the half-wave rectifier with the diode replaced with a realistic model. (c) Transfer characteristic of the rectifier circuit. (d) Input and output waveforms, assuming that r D << R. The bridge rectifier: (a) circuit; (b) input and output waveforms. Full-wave rectifier utilizing a transformer with a center-tapped secondary winding: (a) circuit; (b) transfer characteristic assuming a constant- voltage-drop model for the diodes; (c) input and output waveforms. Calculation of the DC Component (ideal case) For the half wave rectifier, The time average of the current in the load For the full wave rectifier, The time average of the current in the load p L d c d c L p T T T L p T L d c V R I V R V d t d t t R V T d t t i T I = = = + = = 2 2 ) s i n ( 1 ) ( 1 p L dc dc L p T T T L p L p T L dc V R I V R V dt t R V dt t R V T dt t i T I 2 2 ) sin( ) sin( 1 ) ( 1 2 2 = = = + = = (a) The effect of a filter capacitor. (b) Input and output waveforms assuming an ideal diode. The circuit provides a dc voltage equal to the peak of the input sine wave. (peak detector) Voltage and current waveforms in the peak rectifier circuit with CR >> T - = + C fR V V V V L p dc 4 1 1 2 min max Waveforms in the full-wave peak rectifier. Block diagram of a dc power supply Semiconductors Conduction made by electrons that break loose from their bonding structure due to thermal energy Hole movement is as if a positive charge is moving in the opposite direction of the electrons movement Two-dimensional representation of the silicon crystal. The circles represent the inner core of silicon atoms, with +4 indicating its positive charge of +4q, which is neutralized by the charge of the four valence electrons. Observe how the covalent bonds are formed by sharing of the valence electrons. At 0 K, all bonds are intact and no free electrons are available for current conduction. At room temperature, some of the covalent bonds are broken by thermal ionization. Each broken bond gives At room temperature, some of the covalent bonds are broken by thermal ionization....
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EECE312_Ch_02_Semic - Chapter 2: Semiconductors Devices and...

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