Ipakethe ye-MOSFET yokuTshintsha ukuKhethwa kweThubhu kunye neMizobo yeSekethe

Inyathelo lokuqala kukwenza ukhetho lweIi-MOSFETs, eziza kwiindidi ezimbini eziphambili: i-N-channel kunye ne-P-channel. Kwiinkqubo zamandla, ii-MOSFET zinokucingelwa njengezitshixo zombane. Xa i-voltage echanekileyo yongezwa phakathi kwesango kunye nomthombo we-N-channel MOSFET, ukutshintsha kwayo kuqhuba. Ngexesha lokuqhuba, umsinga unokuhamba ngokutshintsha ukusuka kwi-drain ukuya kumthombo. Kukho ukuchasana kwangaphakathi phakathi komsele kunye nomthombo obizwa ngokuba yi-RDS (ON). Kufuneka kucace ukuba isango le-MOSFET sisikhululo se-impedance terminal, ngoko ke i-voltage ihlala yongezwa esangweni. Oku kukuchasana kumhlaba apho isango liqhagamshelwe kulo kumzobo wesiphaluka owenziwe kamva. Ukuba isango lishiywe lijinga, isixhobo asiyi kusebenza njengoko siyilelwe kwaye sinokuvula okanye sivale ngamaxesha angafanelekanga, okukhokelela ekulahlekelweni kwamandla okunokwenzeka kwinkqubo. Xa i-voltage phakathi komthombo kunye nesango i-zero, i-switch iyacima kwaye yangoku iyeka ukuhamba ngesixhobo. Nangona isixhobo sicinyiwe okwangoku, kusekho into encinci yangoku, ebizwa ngokuba yi-leakage current, okanye i-IDSS.

Inyathelo 1: Khetha isitishi esingu-N okanye i-P

Inyathelo lokuqala ekukhetheni isixhobo esichanekileyo soyilo kukwenza isigqibo sokuba sisebenzise i-N-channel okanye i-P-channel MOSFET. kwisicelo samandla esiqhelekileyo, xa i-MOSFET ibekwe phantsi kwaye umthwalo uqhagamshelwe kumbane we-trunk, ukuba i-MOSFET yenza iswitsha yecala lombane ophantsi. Kwi-low voltage side switch, i-N-channelI-MOSFETkufuneka isetyenziswe ngenxa yokuqwalaselwa kwamandla ombane afunekayo ukucima okanye ukuvula isixhobo. Xa i-MOSFET iqhagamshelwe ebhasini kwaye umthwalo uphantsi, iswitshi yecala lombane ophezulu kufuneka isetyenziswe. I-P-channel MOSFET idla ngokusetyenziswa kule topology, kwakhona kuqwalaselo lokuqhuba kombane.

Inyathelo 2: Misela umlinganiselo wangoku

Inyathelo lesibini kukukhetha ireyithingi yangoku ye-MOSFET. Ngokuxhomekeke kwisakhiwo sesekethe, eli nqanaba langoku kufuneka libe ngowona mzuzu uphezulu onokuwuthwala umthwalo phantsi kwazo zonke iimeko. Ngokufana nemeko yombane, umyili kufuneka aqinisekise ukuba i-MOSFET ekhethiweyo inokumelana nolu mlinganiselo lwangoku, naxa inkqubo ivelisa imisinga ye-spike. Amatyala amabini angoku aqwalaselwayo yimowudi eqhubekayo kunye ne-pulse spikes. Le parameter isekwe kwityhubhu ye-FDN304P DATASHEET njengesalathiso kwaye iiparamitha ziboniswe kumzobo:

Kwimo eqhubekayo yokuqhuba, i-MOSFET ikwimo ezinzileyo, xa ikhoyo ngoku ihamba ngokuqhubekayo kwisixhobo. I-Pulse spikes kuxa kukho umyinge omkhulu wokutyanda (okanye i-spike current) ehamba ngesixhobo. Emva kokuba ubuninzi bangoku phantsi kwezi meko sele buchongiwe, yinto nje yokukhetha ngokuthe ngqo isixhobo esinokumelana nalo mbane uphezulu.

Emva kokukhetha i-current rated, kufuneka kwakhona ubale ilahleko yokuqhuba. Enyanisweni, iI-MOSFETayisosixhobo esifanelekileyo, kuba kwinkqubo yokuqhuba kuya kubakho ukulahleka kwamandla, okubizwa ngokuba yilahleko yokuqhuba. I-MOSFET kwi "on" njengokumelana okuguquguqukayo, okugqitywe yi-RDS yesixhobo (ON), kunye nobushushu kunye notshintsho oluphawulekayo. Ukutshatyalaliswa kwamandla kwesixhobo kungabalwa kwi-Iload2 x RDS (ON), kwaye ekubeni i-resistance on-resistance ihluka ngeqondo lokushisa, ukuchithwa kwamandla kuyahluka ngokulinganayo. Iphezulu i-voltage ye-VGS esetyenziswa kwi-MOSFET, encinci i-RDS (ON) iya kuba; ngokuchaseneyo nokuphezulu i-RDS(ON) iya kuba. Kumyili wenkqubo, kulapho urhwebo lungena khona ngokuxhomekeke kumbane wenkqubo. Kuyilo oluphathwayo, kulula (kwaye kuxhaphake ngakumbi) ukusebenzisa amandla ombane asezantsi, ngelixa kuyilo lwemizi-mveliso, kunokusetyenziswa amandla ombane aphezulu. Qaphela ukuba i-RDS (ON) ukuxhathisa inyuka kancinane ngoku. Ukwahluka kwiiparitha ezahlukeneyo zombane ze-RDS (ON) ukuchasana kunokufumaneka kwiphepha ledatha yezobugcisa elinikezelwe ngumenzi.

Inyathelo lesi-3: Misela iiMfuno zeThermal

Inyathelo elilandelayo ekukhetheni i-MOSFET kukubala iimfuno ze-thermal zesistim. Umyili kufuneka athathele ingqalelo iimeko ezimbini ezahlukeneyo, eyona meko imbi kunye neyenyani. Ukubalwa kweyona meko imbi kakhulu kuyacetyiswa kuba esi siphumo sibonelela ngomda omkhulu wokhuseleko kwaye siqinisekisa ukuba inkqubo ayiyi kusilela. Kukwakho nemilinganiselo ethile ekufuneka iqwalaselwe kwiphepha ledatha le-MOSFET; njengokumelana ne-thermal phakathi kwe-semiconductor junction yesixhobo esipakishweyo kunye nokusingqongileyo, kunye nobushushu obuphezulu besiphambuka.

Ubushushu be-junction yesixhobo bulingana nobushushu obuphezulu be-ambient kunye nemveliso yokumelana ne-thermal kunye nokuchithwa kwamandla (iqondo lokushisa elidibeneyo = ubushushu obuphezulu be-ambient + [ukuxhathisa kwe-thermal × ukuchithwa kwamandla]). Ukusuka kolu mlinganiso ubuninzi bokuchithwa kwamandla kwenkqubo kunokusombululeka, okuchazwa ngokulingana ne-I2 x RDS (ON). Ekubeni abasebenzi banqume ubuninzi bangoku oza kudlula kwisixhobo, i-RDS (ON) ingabalwa ngamaqondo okushisa ahlukeneyo. Kubalulekile ukuba uqaphele ukuba xa ujongene neemodeli ezilula ze-thermal, umyili kufuneka acinge kwakhona umthamo wokushisa we-semiconductor junction / device case kunye nemeko / indalo; oko kukuthi, kuyafuneka ukuba ibhodi yesekethe eprintiweyo kunye nephakheji musa ukufudumala ngokukhawuleza.

Ngokwesiqhelo, i-PMOSFET, kuya kubakho i-parasitic diode ekhoyo, umsebenzi wediode kukuthintela uqhagamshelo lokubuyela umva komthombo, kwi-PMOS, inzuzo ngaphezulu kwe-NMOS kukuba i-voltage yokuvula inokuba yi-0, kunye nomahluko wombane phakathi kombane. I-voltage ye-DS ayininzi, ngelixa i-NMOS ikwimeko ifuna ukuba i-VGS ibe nkulu kunomgubasi, okuya kukhokelela kulawulo lombane ngokungenakuphepheka kunombane ofunekayo, kwaye kuya kubakho. ingxaki engeyomfuneko. I-PMOS ikhethwa njengotshintsho lolawulo kwezi zicelo zimbini zilandelayo:

Ubushushu be-junction yesixhobo bulingana nobushushu obuphezulu be-ambient kunye nemveliso yokumelana ne-thermal kunye nokuchithwa kwamandla (iqondo lokushisa elidibeneyo = ubushushu obuphezulu be-ambient + [ukuxhathisa kwe-thermal × ukuchithwa kwamandla]). Ukusuka kolu mlinganiso ubuninzi bokuchithwa kwamandla kwenkqubo kunokusombululeka, okuchazwa ngokulingana ne-I2 x RDS (ON). Ekubeni umyili unqume ubuninzi bangoku oza kudlula kwisixhobo, i-RDS (ON) ingabalwa ngamaqondo okushisa ahlukeneyo. Kubalulekile ukuba uqaphele ukuba xa ujongene neemodeli ezilula ze-thermal, umyili kufuneka acinge kwakhona umthamo wokushisa we-semiconductor junction / device case kunye nemeko / indalo; oko kukuthi, kuyafuneka ukuba ibhodi yesekethe eprintiweyo kunye nephakheji musa ukufudumala ngokukhawuleza.

Ngokwesiqhelo, i-PMOSFET, kuya kubakho i-parasitic diode ekhoyo, umsebenzi wediode kukuthintela uqhagamshelo lokubuyela umva komthombo, kwi-PMOS, inzuzo ngaphezulu kwe-NMOS kukuba i-voltage yokuvula inokuba yi-0, kunye nomahluko wombane phakathi kombane. I-voltage ye-DS ayininzi, ngelixa i-NMOS ikwimeko ifuna ukuba i-VGS ibe nkulu kunomgubasi, okuya kukhokelela kulawulo lombane ngokungenakuphepheka kunombane ofunekayo, kwaye kuya kubakho. ingxaki engeyomfuneko. I-PMOS ikhethwa njengotshintsho lolawulo kwezi zicelo zimbini zilandelayo:

Ukujonga le sekethi, uphawu lolawulo lwe-PGC lulawula ukuba i-V4.2 inikezela ngamandla kwi-P_GPRS. Le sekethi, umthombo kunye neetheminali zokuhambisa amanzi aziqhagamshelwanga ngasemva, i-R110 kunye ne-R113 zikho ngengqiqo yokuba isango lolawulo le-R110 langoku alikho likhulu kakhulu, i-R113 ilawula isango lesiqhelo, i-R113 yokutsala ukuya phezulu, ukusuka kwi-PMOS. , kodwa kwakhona kunokubonwa njengokutsalwa-phezulu kwisiginali yokulawula, xa izikhonkwane zangaphakathi ze-MCU kunye nokutsalwa, oko kukuthi, imveliso ye-drain evulekileyo xa imveliso ivulekile, kwaye ayikwazi ukuyiqhuba i-PMOS, ngeli xesha, kuyafuneka amandla ombane angaphandle anikwe ukutsalwa, ngoko ke i-resistor R113 idlala iindima ezimbini. Kuya kufuneka i-voltage yangaphandle ukunika ukutsalwa, ngoko ke i-resistor R113 idlala iindima ezimbini. I-r110 inokuba ncinci, ukuya kwi-100 ohms nayo ingabakho.