Applications Of Transistor At A Glance

1. Applications of Transistors
The transistoras an amplifier
1. A transistorcan be usedtoamplifycurrent.Thisisbecause asmall change in base currentcausesa
large change in collectorcurrent.
2. Example isa microphone.
3. Soundwavesthat are fed intothe microphone cause the diaphragminthe microphone tovibrate.
4. The electrical outputof the microphone changesaccordingtothe soundwaves.
5. As a result,the base currentis varyingbecause of the small alternatingvoltage producedbythe
microphone.
6. A small change inthe base currentcausesa large change inthe collectorcurrent.
7. The varyingcollectorcurrentflowsintothe loudspeaker.There,itischangedintothe soundwaves
correspondingtothe original soundwaves.
8. The frequenciesof bothwavesare equivalentbutthe amplitude of the soundwave fromthe
loudspeakerishigherthanthe soundwavesfedintothe microphone.
Component:Function
Microphone:To change soundsignal toelectrical signal
Capacitor:To blocka steadycurrentfromflowingintothe transistorandmicrophone.
Potential divider:Toapplya proportionof the total voltage acrossthe emitter-base junctionsothatthe
junctionisforward-biased.
Transistor:To amplifythe inputwave form.
Loudspeaker:Tochange the electrical signal tosoundwave.
The transistoras switch
1. In a transistor,nocurrentcan flowinthe collectorcircuitunlessacurrentflowsinthe base circuit.
Thispropertyallowsatransistorto be usedas switch.
2. The transistorcan be turnedon or off by changingthe base.

2. 3. There are a fewtypesof switchingcircuitsoperatedbytransistors.
(a) Light-OperatedSwitch
1. The circuitis designedtolightthe bulbinabrightenvironmentandtoturn it off inthe dark.
2. One of the componentsinthe potential dividerisalight-dependentresistor(LDR).Whenitisplaced
inDARKNESS,itsresistance islarge.The transistorisswitchedOFF.
3. When LDR islightedbybrightlight,itsresistance fallstosmall value resultinginmore supplyvoltage
and raisingthe base current.The transistorisswitchedon,collectorcurrentflowsandbulblightsup.
(b) Heat-operatedswitch
1. One importantcomponentinthe circuitof a heat-operatedswitchisthe thermistor.
2. Thermistoristype of resistorthat respondstothe surroundingtemperature.Itsresistanceincreases
whenthe temperature islowandvice versa.
3. When heatisappliedtothe thermistor,itsresistance dropsandagreatershare of supplyvoltage is
droppedacross R. The base currentincreasesfollowedbyagreaterincrease inthe collectorcurrent.The
bulbwill glowandthe sirenwill sound.
4. This particularcircuitissuitable asa fire alarmsystem.
(C)IntegratedCircuits
1. An integratedcircuit(IC) consistsof transistors,resistors,diodesandcapacitorscombinedtogetherin
one wafer-thinchipof silicon.
2. This isone wafer-thinchipiscalledamicrochip.
3. The microchipisonlya fewmillimeterssquare withathicknessof 0.5mm.
Advantagesof anIC:
a. Consumesasmall amountof electrical energy.
b. Verylittle heatisgenerated.
c. Occupiesa small space whichreducesthe size of circuits.

3. d. Can be builtat lowcost.