www.getmyuni.com Chapter 16 Other Two-Terminal Devices 11 www.getmyuni.com owT seciveDrehtOo-wTowT lanimreT rehtO rehtO--seciveD owTseciveD rehtO lanimreT- lanimreT seciveD lanimreT odideShcott ky odideShcott ky odide aartcorV odide aartcorV odidse reoPw odidse reoPw odide unnleT odide unnleT hPoteoodid hPoteoodid sllec ehPvoitoutcocnd sllec ehPvoitoutcocnd ttismreeIR ttismreeIR asplydisyrcsta ldq uiiL asplydisyrcsta ldq uiiL sllec Soalr sllec Soalr stiomhrserT stiomhrserT iaCrcneDd1vTuh 0iei/etoc lEryeec,s t ronic 2 2 aNaLsoBnoyLdhu. eli lesoRssb ektrat dy www.getmyuni.com DodeiShcottky DodeiShcottky arbrierAlso called ar-brier arbrier ycottkSh-, ar-brier ycottkShcarrier rufacse-, or -carrier rufacse ot-hdiode. oth arhacCtertiicss arhacCtertiicss (Compared with general-purpose diodes) • Lower forward voltage drop (0.2-.63V) • Higher forward current (up to 75A) • Significantly lower PIV • Higher reverse current • Faster switching rate snoitacilppAApplications snoitacilppA gnihciswt ycneuqfre higH•High frequency switching gnihciswt ycneuqfre higH snoitacilppaapplications snoitacilppa hihgwLo• egatlovLow- Low---voltage wLovoltage tnerruc high-high---current hihgcurrent egatlov tnerruc snoitacilppaapplications snoitacilppa sretrevnoc•CAAC- AC---to CA tototo-CD---DCDC converters sretrevnoc CD tnempiuqe noitacinummoC•Communication equipment tnempiuqe noitacinummoC stiuicrc noitatnemurstIn•Instrumentation circuits stiuicrc noitatnemurstIn Electronic Devices and Circuit Theory, 10/e 33 Robert L. Boylestad and Louis Nashelsky www.getmyuni.com edoiD rotcaraVVaractor Diode edoiD rotcaraV Also calledvacapir a VVC vacapir, VVC(voltage- variable capacitance),odidetnugni or odidetnugni. It basically acts like a variable capacitor. Electronic Devices and Circuit Theory, 10/e 44 Robert L. Boylestad and Louis Nashelsky www.getmyuni.com noitarepO edoiD rotcaraVVaractor Diode Operation noitarepO edoiD rotcaraV A reverse-biased varactor acts like a capacitor. Furthermore, the amount of reverse bias voltage determines the capacitance. As VR increases the capacitance decreases. C(0) C)=== T(VR n 1(+++ VRT V ) where C(0) = the capacitance with no reverse bias applied 1 1 n = /2 for alloy and /3 for diffused junctions VT = maximum reverse bias voltage VR = applied reverse bias voltage Electronic Devices and Circuit Theory, 10/e 55 Robert L. Boylestad and Louis Nashelsky www.getmyuni.com snoitacilppA edoiD rotcaraVsnoitacilppA edoiD rotcaraV snoitacilppA edoiD rotcaraV omadultoMFr omadultoMFr sedvcei lorntoc sedvcei lorntoc-yc-qenerf ycqenerf-Aut-coiamt Autcoiamt tsrelfibandpass Adj eustlab tsrelfibandpass Adj eustlab srefaiipmlaP acrteimr srefaiipmlaP acrteimr iaCrcneDd1vTuh 0iei/etoc lEryeec,s t ronic 6 6 aNaLsoBnoyLdhu. eli lesoRssb ektrat dy www.getmyuni.com sedoiD rewoPPower Diodes sedoiD rewoP • Power diodes used in high-power and high-temperature applications, such as power rectifier circuits, must be rated for power • Power diodes are sometimes referred to as rectifiers • They have the same symbol and operation as a general- purpose diode • Power diodes are physically larger than general-purpose diodes, and they require heat sinking. Electronic Devices and Circuit Theory, 10/e 77 Robert L. Boylestad and Louis Nashelsky www.getmyuni.com sedoiD lennuTTunnel Diodes sedoiD lennuT A tunnel diodengeavt has aie ngeavt ie stsiaenecr stsiaenecrregion, which means its current decreases as the forward-bias voltage increases. Electronic Devices and Circuit Theory, 10/e 88 Robert L. Boylestad and Louis Nashelsky www.getmyuni.com sedoiD lennuTTunnel Diodes sedoiD lennuT naOpreoti naOpreoti The characteristics of the tunnel diode indicate the negative resistance region. Note that this is only a small region of the characteristic curve. If the forward bias voltage is beyond the negative resistance region, the tunnel diode acts like a general-purpose diode. If the forward bias voltage is in the negative resistance region then the diode can be used as an oscillator. Electronic Devices and Circuit Theory, 10/e 99 Robert L. Boylestad and Louis Nashelsky www.getmyuni.com snoitacilppA edoiD lennuTsnoitacilppA edoiD lennuT snoitacilppA edoiD lennuT tusciricqeyec frgHih tusciricqeyec frgHih asrltloiOsc asrltloiOsc ontekrswntghcii Sw ontekrswntghcii Sw ganreetosr seuPl ganreetosr seuPl srefiAipml srefiAipml iaCrcneDd1vTuh 0iei/etoc lEryeec,s t ronic 10 10 aNaLsoBnoyLdhu. eli lesoRssb ektrat dy www.getmyuni.com sedoidotohPPhotodiodes sedoidotohP A photodiode conducts when light is applied to the junction. naOpreoti naOpreoti The photodiode is operated in reverse bias. When light of a particular wavelength strikes the junction it conducts. The higher the intensity of light (measured in foot-candles), the higher the conduction through the photodiode. ascAotippinl ascAotippinl • Instrumentation circuits as a sensor • Alarm system sensor • Detection of objects on a conveyor belt Note that the diode conducts somewhat with no light applied, this is called the dark current. Electronic Devices and Circuit Theory, 10/e 11 11 Robert L. Boylestad and Louis Nashelsky www.getmyuni.com slleC evitcudnocotohPPhotoconductive Cells slleC evitcudnocotohP eOpration eOpration A photoconductive cell varies resistance with intensity of light. Like a common resistor, a photoconductive cell has no polarity and can be placed into the circuit in either direction. lipc psatiAon lipc psatiAon • Light/darkness detection • Controlling intensity of lighting systems Electronic Devices and Circuit Theory, 10/e 12 12 Robert L. Boylestad and Louis Nashelsky www.getmyuni.com srettimE RIIR Emitters srettimE RI These are diodes that emit IR (infrared radiation) noitarepOOperation noitarepO IR emitter produce infrared radiation when forward biased. The higher the forward bias current, the greater the intensity of infrared radiation. The radiation pattern can vary from widely dispersed to a very narrow, focused beam. lipcpsatiAon lipcpsatiAon eeadrsrar ••Cd eeadrsrar Cd eeafnrt hsS•• eeafnrt hsS alar imstonrsnuI•• alar imstonrsnuI mirtsteanrsT•• RI mirtsteanrsT RI Electronic Devices and Circuit Theory, 10/e 13 13 Robert L. Boylestad and Louis Nashelsky www.getmyuni.com )sDCL( syalpsiD latsyrC diuqiLLiquid Crystal Displays (LCDs) )sDCL( syalpsiD latsyrC diuqiL There are two varieties—those with a light background and dark display or those with a dark background and light display. eOpration eOpration The background is either light or dark, when a voltage is applied to a segment then the alphanumeric display is visible. The amount of voltage necessary for display varies depending on the type of display, from 2 to 20V. Low power LCDs require less power than LEDs. But LEDs have faster response times and longer life. lipcpsatiAon lipcpsatiAon • Digital clocks • Digital thermometers • Odometers Electronic Devices and Circuit Theory, 10/e 14 14 Robert L. Boylestad and Louis Nashelsky www.getmyuni.com slleC raloSSolar Cells slleC raloS Solar cells produce a voltage when subjected to light energy. The greater the light intensity, the greater amount of voltage produced. Electronic Devices and Circuit Theory, 10/e 15 15 Robert L. Boylestad and Louis Nashelsky www.getmyuni.com srotsimrehTThermistors srotsimrehT Thermistors are resistors whose value changes with temperature. eOpration eOpration Thermistors are negative-coefficient devices—their resistance decreases as the temperature increases. lipcpsatiAon lipcpsatiAon • Sensors in instrumentation circuits • Temperature correction circuitry Electronic Devices and Circuit Theory, 10/e 16 16 Robert L. Boylestad and Louis Nashelsky.