Nrog txoj kev loj hlob sai ntawm cov thev naus laus zis niaj hnub no, LED (Light Emitting Diode), ua kom muaj txiaj ntsig zoo, txuag hluav taws xob, thiab kev siv hluav taws xob zoo ib puag ncig, tau maj mam dhau los ua ib feem tseem ceeb ntawm tib neeg lub neej. Txawm li cas los xij, thaum peb xav txuas lub LED rau lub zog hluav taws xob, peb puas tuaj yeem txuas ncaj qha rau LED mus rau 12V roj teeb? Qhov teeb meem no muaj qee qhov kev paub txog hluav taws xob thiab circuits, cia peb delve tob rau hauv nws.
Raws li cov khoom siv semiconductor, LED yog tus cwj pwm los ntawm qhov yuav tsum tau ua haujlwm nyob rau hauv qhov tsim nyog voltage thiab tam sim no thiaj li yuav emit lub teeb ib txwm. Feem ntau hais lus, qhov hluav taws xob ua haujlwm ntawm LED yog nyob rau hauv qhov kev teev tseg, thiab tshaj lossis poob qis hauv qab no yuav ua rau LED ua haujlwm tsis zoo lossis puas tsuaj. Yog li ntawd, thaum xav txog kev sib txuas ntawm LED mus rau 12V roj teeb, peb yuav tsum xub nkag siab txog qhov kev ua haujlwm ntawm LED.
Feem ntau cov LED khiav hauj lwm voltages ntawm 2V txog 3.5V. Qhov no txhais tau hais tias yog ib qho LED nrog lub zog ua haujlwm ntawm 3V ncaj qha mus rau 12V roj teeb, nws yuav ua rau qhov hluav taws xob siab dhau thiab tuaj yeem ua rau LED puas. Txhawm rau ua kom lub zog ua haujlwm ib txwm muaj ntawm LED, peb yuav tsum ntxiv cov resistors tsim nyog ntawm LED thiab lub roj teeb kom txwv qhov tam sim no. Qhov no yuav pab txo cov roj teeb hluav taws xob mus rau hauv qhov yuav tsum tau ua haujlwm voltage ntau ntawm LED, thaum tiv thaiv LED los ntawm kev puas tsuaj ntau dhau tam sim no.
Thaum tsim cov resistors, peb tuaj yeem siv Ohm txoj cai los xam cov nqi tiv thaiv. Ohm txoj cai tau hais tias V{{0}} IR, qhov twg V yog qhov voltage, kuv yog tam sim no, thiab R yog qhov tsis kam. Piv txwv tias LED yuav tsum tau ua haujlwm tam sim no ntawm 20mA (0.02A) thiab ua haujlwm voltage ntawm 3V, txuas rau 12V roj teeb. Peb tuaj yeem suav tus nqi tiv thaiv uas yuav tsum tau siv Ohm txoj cai:
12V -3V=9V (qhov hluav taws xob poob rau LED)
Kuv =0.02A (LED tam sim no)
Raws li Ohm txoj cai, R{{0}}V/I=9V/0.02A=450 Ω
Yog li ntawd, peb yuav tsum tau txuas lub resistor ntawm kwv yees li 450 Ω los txwv qhov tam sim no kom ntseeg tau tias LED tuaj yeem ua haujlwm ib txwm ntawm 12V roj teeb. Qhov no resistor yuav haus ntau dhau voltage, kom ntseeg tau tias LED tau txais qhov tseeb tam sim no thiab voltage.
Nws yuav tsum raug sau tseg tias cov qauv sib txawv, xim, thiab lub zog ntawm LEDs muaj qhov sib txawv ntawm kev ua haujlwm. Yog li ntawd, thaum txuas LEDs, peb yuav tsum sab laj cov LED specifications kom tau qhov tseeb kev khiav hauj lwm voltage thiab tam sim no tus nqi. Tsis tas li ntawd, lub zog ntawm tus resistor kuj yuav tsum tau txiav txim siab kom ntseeg tau tias tus resistor tsis overheat. Cov mis laij lej fais fab P=IV tuaj yeem siv tau, qhov twg P yog lub zog, Kuv yog tam sim no, thiab V yog qhov hluav taws xob los xam qhov yuav tsum tau muaj zog tiv thaiv.
Hauv cov ntsiab lus, txawm hais tias LEDs tuaj yeem txuas nrog 12V roj teeb, nws yog ib qho tsim nyog yuav tsum tau them sai sai rau qhov kev khiav hauj lwm voltage thiab tam sim no cov kev cai ntawm LEDs. Txhawm rau kom ntseeg tau tias kev ua haujlwm ib txwm muaj thiab kev ua neej nyob ntawm LEDs, peb yuav tsum siv cov resistors tsim nyog los txwv tam sim no thiab xyuas kom meej tias lub zog ntawm cov resistors tsis dhau. Nws yog ib qho tseem ceeb kom nkag siab txog cov lus qhia tshwj xeeb ntawm LED thiab qee qhov kev paub txog hluav taws xob yooj yim thaum txuas mus rau lub zog hluav taws xob, txhawm rau kom tsis txhob ua rau LED puas thiab ua tiav cov teeb pom kev zoo tshaj plaws.
