ELTE 1403

Forward biased : Varactor is a silicon diode optimized for its Varactor variable capacitance when reversed- biased. Used for tuning frequency- cathode anode dependent equipment.

Zener Diode is designed to operate in the Zener electron breakdown region; used for N P flow regulation.

+ depletion layer Avalanche Effect Reverse voltage exceeds the breakdown voltage and the minority carriers are given An ideal diode acts like a closed switch when forward enough energy to dislodge valence electrons from biased and an open switch when reverse biased. 1st their orbits. These free electrons then dislodge approximation calculations assume an ideal diode. others. 2nd approximation calculations take into account the Zener Effect The electric field becomes strong enough voltage drop across the diode. 3rd approximation across the junction of a heavily-doped reverse-biased calculations additionally take into account bulk diode to pull valence electrons from their shells. For resistance. breakdown below 5V, the Zener effect Voltage Drop silicon diode .7V germanium diode .3V dominates, above 6V the avalanche effect dominates. Second Approximation for a Zener Diode Bulk Resistance rB = DE/DI A digital multimeter won't measure the resistance on a Iz = zener current V = supply voltage diode due to insufficient voltage. The diode check Vin -Vz in I z = R + R Vz = zener voltage function of a digital multimeter reads the knee s z R = source resistance voltage. The knee voltage is the voltage at which a s Rz = zener resistance forward biased diode begins to conduct. Zener Resistance is the small series resistance of a zener diode when it operates in the breakdown region.

Diode Ratings: DVout = DIz Rz DV = change in output voltage PIV Reverse Breakdown Voltage DIz = change in zener current R = zener resistance If Forward Current Limit z IS Saturation Current - minority carrier current of a reverse-biased diode R Forward Resistance Vp V 2 f Half-Wave Rectifier: V = = rms Vk Knee Voltage dc p p

diode reverse voltage: PIV = Vp

Light Emitting Diode When forward-biased, diode forward current: I diode = Idc free electrons combine with holes near the LED junction. As they move from an area of Half-Wave Rectifier With PIV = 2Vp higher energy to lower energy, they emit Capacitor Filter: radiation. Assume 2V drop unless specified. Vdc = Vp = Vrms 2

Schottky Diode has almost no charge storage, so can switch on and off much Schottky Vp V 2 Full-Wave Rectifier: V = = rms faster than an ordinary diode. Has dc p p metallic/silicon junction; low power V is the voltage across the full secondary winding) handling; .25V offset voltage; used for high p frequencies. diode reverse voltage: PIV = Vp 1 diode forward current: I diode = 2 I dc

Tom Penick [email protected] www.teicontrols.com/notes 06/12/98 Full-Wave Rectifier With V = 1 V = 1 V 2 Capacitor Filter: dc 2 p 2 rms Bias: difference in potential between base and emitter.

2V Base Bias p Vrms 2 2 DC Alpha: I Bridge Rectifier: V = = a = C VBB VCC dc p p (slightly less DC than 1) I E diode reverse voltage: PIV = Vp RB R C b diode forward current: I = 1 I a = DC diode 2 dc DC IB IC bDC +1 DC Beta: Bridge Rectifier With I C Vdc = Vp = Vrms 2 (usually 50 - b = Capacitor Filter: DC I V 300) B Further refined to include rip IE V = .7V the effect of ripple voltage: Vdc = Vp - BE 2 hFE is the same as bDC, the collector to emitter current gain Ripple Formula for a Vrip = peak-to-peak ripple The four operating regions of a are saturation, capacitor-input filter Idc = dc peak load current active, cutoff, and breakdown. f = ripple frequency (twice DC and AC Load Lines, Q Point I the input frequency for a V = dc I rip f C full-wave rectifier) C C = filter capacitance VCEQ V + I r ICQ + AC load line CEQ CQ L rL I C(SAT) DC load line A choke is an iron-core inductor with a Q VCE(CUTOFF) large value of L in Henrys. The X L = 2pf L choke has an inductive reactance in VCE ohms of: The DC Load Line is a graph representing all possible dc A capacitor has an inductive reactance 1 operating points of the transistor for a specific load in ohms of: X C = 2pfC . VCE is the x-axis and IC is the y-axis. The equation is V = V - I R . The horizontal The resonant frequency of an inductor 1 CE CC C C and capacitor (or varactor) in f = intercept will be the supply voltage VCC and the parallel: 2p LC vertical intercept will be the collector current when the transistor is saturated, i.e. the collector/emitter is considered a closed switch. Clipper: Removes either the positive or negative peaks The Q Point is the operating point of the transistor, of a sine wave by shorting through a diode. usually located near the middle of the DC Load Line AC Load Line The Q point Clamper: Raises or lowers the sine wave so that it VCEQ moves along the AC load i = I + becomes mostly positive or mostly negative. c(sat) CQ r Or Gate: Output goes high when any input is high. line. Steeper than the DC L load line. And Gate: Output goes high when all inputs are high vce(cutoff ) = VCEQ + ICQrL AC Compliance - maximum peak to peak AC output voltage without clipping. AC Compliance is calculated by finding the smaller of the following: heavily lightly npn Cutoff Clipping: Saturation Clipping: doped doped n n PP = 2ICQrL PP = 2VCEQ Emitter Base Collector p When the Q point is centered on the DC load line, cutoff clipping occurs first because the AC load line is always n p n steeper than the DC load line. DC Compliance is the DC voltage range over which the pnp p p transistor can operate; in other words VCC. IE IB IC electron flow n

(the n is next to forward biased reverse biased the arrow)

IE = IB + IC VCE = VCC - IC RC

Tom Penick [email protected] www.teicontrols.com/notes 06/12/98 Voltage Divider Bias: The Base Bias VCC AC Emitter Resistance of a Transistor: 25mV circuit above is usually impractical re¢ = in linear circuits because the Q IE R1 RC point is unpredictable due to variations in bDC. The Voltage I AC Beta: Called b as opposed to bdc (DC i C b = c Divider Bias shown at right solves Beta). Referred to as hfe as opposed to ib this problem. When bDC is known, hFE for DC Beta. I may be calculated as: E CE Characteristics: VCC VB -VBE Output is out of I @ IE E R + (R R ) /b phase with input E 1 2 dc High voltage gain is R1 RC R2 RE possible R1 R2 But when RE >> , May be used with a RL bdc swamping resistor to stabilize the VB -VBE the equation may be reduced to: I @ voltage gain E R In a matched load E R2 RE 1) Calculate the voltage at the base condition, RL = RC 2) The emitter voltage is .7 less than the base 3) Calculate I E AC Input Impedance of CE 4) I @ I zin = R1 R2 bre¢ C E : 5) Calculate voltage drop across RC AC Voltage Gain (CE) when the Vout rL emitter is AC ground: A = = When designing the voltage divider bias amplifier, the V r¢ current through the voltage divider should be at least in e Swamping Resistor To 10 times the current through the base. zin(base) = b(rE + re¢) To center Q on the DC load line, V will be ½V , V will desensitize a CE amplifier to CE CC E ¢ be about .1VCC. changes in r’e, a resistor rE is zin = R1 R2 b(rE + re ) To center Q on the AC added between the emitter and VCC r load line, use the I = ac ground. This stabilizes the A = L CQ amount of gain, but also formula: RC + RE + rL rE + re¢ reduces it. Heavy Swamping The value of Other Methods zin = R1 R2 brE rE is much larger than the value Emitter Collector r Emitter Bias of r’e: A = L Feedback Bias Feedback Bias r V V E CC CC AC Input Voltage when a source v z VCC in in resistor (a resistor in series with vb = RC RB RC the input) is present. Rs + zin RC AC Load Resistance, rL, rc, or rLac, is the parallel RB IC IB IC combination of all AC paths from collector to ground. Remember the battery and capacitors are considered IC IB shorts. AC Power delivered to the load (class A amplifier): where VL is rms: using peak to peak volts: I IB IE E V 2 V 2 I L PP E PL = PL = RB RE R 8R RE L L Quiescent Power Dissipation -VEE PDQ = VCEQ I CQ of a transistor: V -V V -V CC BE CC BE VEE -VBE Efficiency of a stage: P I C @ I C @ I @ L(max) R + R /b R + R /b E PL is load power at AC h = ´100% E B dc C B dc RE compliance PCC Total Current Drain is the voltage AC Resistance of a Diode: I CC = I1 + I CQ 25mV divider current plus the collector current: where I is the dc current through the r = ac Cascaded Stages Gain: diode. To a second approximation, I A = A1 A2 A3 consider the .7V drop across the Cascaded Stages The AC load diode in calculating the value I. resistance of one stage is affected by rL = RC zin the impedance of the following stage:

Tom Penick [email protected] www.teicontrols.com/notes 06/12/98 Field Effect Transistors CC Characteristics: Common Collector Voltage gain < 1 (Emitter Follower) Junction Field Effect Transistor JFET High input impedance VCC N channel P channel AC output is in phase D D Low-distortion R 1 Has power gain G G Can be placed at the output of a CE amplifier to reduce S S output loading and Creating a Never R 2 RE RL thereby increase the depletion region forward Drain gain. by reverse biasing biased n the gate reduces Gate p p Input Impedance (high) of a CC: R R b(r + r¢) (pinches) current 1 2 L e between the drain n AC Voltage Gain of a CC is slightly VGG VDD rL and the source. less than 1: A = Source rL + re¢ AC Power Gain of a CC: rL G = b = bA @ b Metal Oxide Silicon Field Effect Transistors rL + re¢ Enhancement-type MOSFET AC Output Power of a CC: 2 Pout = ie rL N channel P channel D D The Darlington Darlington Pair B B Amplifier VCC G S G S consists of R 1 cascaded CC’s G Gate for a very large Thin silicon increase in D Drain dioxide layer input B Substrate* Metal Drain impedance. S Source n Gate Substrate R R R p 2 E L *usually connected n internally to Source The Zener Follower is a Zener Follower the source voltage regulator circuit that offers improved load Depletion-type MOSFET handling over the zener N channel P channel regulator. Voltage output + is .7V less than the value Vin D D R L of the zener diode. - B B G S G S

Depletion-type MOSFET CB Characteristics: Common Base Low input impedance V MOSFET’s do CC Gate may be Large voltage gain not have thermal Drain AC output in phase runaway. positive or negative Useful at high n frequencies Gate p Substrate Not as popular as CE or CC n R A differential L Source amplifier is a CB driven by a CE

Tom Penick [email protected] www.teicontrols.com/notes 06/12/98