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Reference Guide

Electronics II - Reference Guides

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Electrical Engineering
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permacharts TM E le c t r o n ic sII Operational Amplifiers (OP AMPS) Transistors As Switches • Linear applications involve negative feedback (amplif•These involve positive or no feedback •Where signal at base (gate) determines if switch is on or off smmer DAC andADC,integrators,differentiators,filters,•tIn these cases,the high gain of the op amp causes the outputAR • As a result,the voltage at its input is held at ª 0 to become saturated at either its positive or negative extreme, • “Off”whenBi= 0 fi iE= 0 is the cutoff state • Non-linear applications include comparators,Schmitt triggers,a volt short of the supply voltages • VBE£ 0.3V oscillators,ideal diodes,etc. • If V is made more negative than ª –5 V,then the INVERTING CONFIGURATION DC OFFSET base-emitter junction may break down • (+) and (–) at the input • For real op amps,there is a small DC input offIOt volt•“On”when iB ≥ C / bfiu CEis 0.2V:saturation state indicate the polarity of v and a small DC input bias cBrrent I • uBEis still 0.7V, as in the active state tat makes 0positive •The effect of each is DC offset at the output • i () is inverting input • General purpose op amp has typi=a5 mV ,I= 0.1 mA FIELD-EFFECT TRANSISTOR (FET) terminal because if IO dc B • Modeled by a resistads(on) the“on”state v(–)≠,then Ø SCHMITT TRIGGER • Control is by gate-source voltage i 0 • An op amp alone can be • (i+) indicates used as comparator but • VPtypically –10V to –1V non-inverting input terminal V0 R 2 • ds(on)ypically 30 W to 500 W because ii v≠,then 0Ø V1= − R1 i can chatter • “Off”:u £ V ;On”:u =0 • Gain depends only 1n R a2d R Solution: Schmitt trigger GS P GS • Ideally,v = 0,A•=,R = • ,R = 0 can provide hysteresis by •VFET,DFET,and HEXFET haveds(on)f only a few ohms i in out positive feedback NON-INVERTING CONFIGURATION • Input terminals compare P OWER INVERTER USING EMITTER-COUPLED LOGIC to voltages and output Example: Converts is either +14 or –14, power at 12dcto power at 118ac depending on which input voltage is higher υ0 = R1 2 υ 1 R1 VOLTAGE FOLLOWER • u = u o 1 OSCILLATOR • Only purpose is buffering • Schmitt trigger can be modified to make an oscillator to generate a square wave • As with Schmitt m trigger,ueeps o DIFFERENTIAL CONFIGURATION changing due to • If1u is grounded,then positive feedback c u2sees an inverting . configuration • Negative feedback • If uis grounded,then u sees produces 1by s a non-inverting configuration charging a capacitor t • Frequency depends on υυ0 112 2± the va
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