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Reference Guide

Conductors & Semiconductors - Reference Guides

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Electrical Engineering
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l e a r n • r e f e r e n c e • r e v i e w permacharts TM CConductors & Semiconductors BASICS TERMS Conductor Valence and conduction bands for electrons Diode Two semiconductor materials fabricated in the overlap at room temperature, allowing relatively form of a PN junction with a semiconductor-metal free movement of electrons junction at each end Semiconductor Valence and conduction bands have an energy Zener Diode Diode constructed so increase in current in reverse gap that can be jumped by a significant number direction (when diode is reverse-biased) will be of thermally excited electrons at room non-destructive temperature, making these materials Frequency Cycles per second • f = 1/t semiconductors • Symbol = f • Common semiconductor materials include • Units = hertz (Hz or s ) silicon and germanium N-type Material Majority of free charge carriers in semiconductor Resistance A measure of the opposition to current flow material are negative • Symbol = R • Units = Ohm (W) Forward-/ Connection across a PN junction • In forward- bias, P-type Material Majority of free charge carriers in semiconductor Reverse-biasing current flows from P-type material to N-type material are positive • In reverse-bias, current flows from N-type Doping Mixing in a few atoms of a different material into material to P-type a semiconductor material, in order to generate Capacitance Ability to store electric charge • Symbol = C more charge carriers (such as, doping a crystal of • Units = Farad (F) pure silicon with arsenic atoms to form N-type material) Electric Current A measure of the flow of electrons • Symbol = I PN Junction Junction of P- and N-type semiconductor materials • Unit = Ampere (A) which develop an electric field across the junctionnsulator Valence and conduction bands for electrons do that repels both majority carriers away from the not overlap at room temperature, and have an junction energy gap that cannot be jumped by electrons at room temperature; this does not allow movement of electrons, making these materials insulators ELECTRIC CIRCUIT APPLICATIONS OF ORDINARY DIODES w RECTIFIERS w • Rectifiers may be half-wave or w full-wave . • A half-wave cuts p off the bottom (or top) of the e input signal r • A full-wave flips bottom of signal m so that both positive and a negative halves c of the AC wave appear across h load resistor a • Half-wave rectifiers produce r an output signal t with a fundamental s frequency that . is same as input c AC signal o • Full-wave rectifiers m double the input AC signal frequency • Power supply applications commonly use a • An operational amplifier may be combined with a physical diode to produce a circuit transformer to isolate the power supply from a that responds like a perfect diode, which is also known as an active full/half-wave 110-V AC line rectifier • A half-wave rectifier may be connected to th• This circuit overcomes forward voltage drop of the conducting diode transformer secondary (as shown) to generate • In an active half-wave rectifier, Daracteristics are being improved, while D only typical half-wave output signal 1 2 provides a current feedback path around the amplifier1when D is not conducting 1 CONDUCTORS & SEMICONDUCTORS • 1-55080-808-7 © 1996-2010 Mindsource Technologies Inc. permachartsM l e a r n • r e f e r e n c e • r e v i e w ELECTRIC CIRCUIT APPLICATIONS OF ORDINARY DIODES (CONT’D) C LAMPING CLIPPING • As an alternative to • A diode clipping circuit is used to limit the voltage swing of a signal connecting a capacitor to • If signal voltage is between limits set by voltage references, then the ground (or some other signal is unaffected as neither diode conducts voltage reference), a DC reference for the • For signal voltage swings beyond limits, appropriate diode conducts, causing additional voltage drop across resistor R output signal may be established using a diode clamp • Clamp allows no part of the wave to go negative CHARGE PUMP • For ideal cases, output voltage of charge pump circuit is proportional to number of input signal pulses, and may be used to INTERGRATED CIRCUIT VOLTAGE REGULATIONS count the number of input pulses during some time interval • This is a transient circuit; a switch is necessary to discharge • A simple power supply circuit using a transformer and rectifier, a capacitor C2between counting intervals and establish a zero-count low-pass filter circuit (i.e., an electrolytic capacitor), and a three voltage reference terminal regulator may be used as a DC supply (as shown) • The most popular units of three terminal regulators provide up to 1 • For step size 2V to be small compared to V, allowing a signal like A output current and are known as 79xx or LM320-xx for negative that shown, value of 1 must be much less than 2 voltages, or 78xx or LM340-xx for positive voltages • Voltage increase on2C is 2V = 1C ÷ (1 + C2)](V -2V ) Note: xx indicates the voltage sizes (for example, 5, 6, 10, 12, 15, 18, and 24) • Values for 1 and C2vary with operation requirements • Minimum size for C is 0.1 µF; a typical value for C is 1 µF 1 2 • Input voltage across regulator must be at least 2.5 volts higher than output voltage; a 5 volt drop across the regulator is commonly used FREQUENCY TO VOLTAGE CONVERTER • Adding a load resistor to a charge pump causes circuit to become a frequency to voltage converter • If 1 2 Rf << 1 + 2 (where f is frequency), then a linear relationship between voltage and frequency is acquired • V = [(C C ) ÷ (C + C )] RVf 2 1 2 1 2 m • Design requirements may be simplified to 2/C << Rf << 11C o c . s t r INDUCTIVE SURGE SUPPRESSION a • When an inductive load is switched out of a circuit, transient voltage surges across the switch (causing sparks, radio frequency h noise, damage to solid state transistor switches, etc.) may be c TABLE OF RESISTIVITIES suppressed using a diode a • (Ohms/meter at room temperature) • For AC current, two Zener diodes (as shown) are used • A series resistor in these diode bypass circuits may be necessary to m Conductors Semiconductors dissipate inductor energy more rapidly, depending on the Q of the r Silver 1.59 x 10-9 Carbon 3.5 x 105 inductor and other circuit considerations Copper
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