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  • 2 22.2 Rezistoare dependente

    ����������$SOLFD LLOH�WHUPLVWRDUHORU�37&

    $SOLFD LLOH�WHUPLVWRDUHORU�37&�VXQW�IRDUWH�QXPHURDVH��FkWHYD�GLQWUH�HOH�ILLQGXUP�WRDUHOH��SURWHF LD�vPSRWULYD�VXSUDFXUHQ LORU�úL�D�VXSUDWHPSHUDWXULL��LQGLFDWRDUHde nivel, circuit de demagnetizare pentru tuburile cinescop color, termostate cuYDORUL�IL[H�DOH�WHPSHUDWXULL��UHOHH�GH�WHPSRUL]DUH��P�VXU�WRUL�GH�WHPSHUDWXU��úL�PDLUDU�FRPSHQVDUHD�YDULD LHL�FX�WHPSHUDWXUD�D�DOWRU�HOHPHQWH�GH�FLUFXLW�

    Cele prezentate la începutul capitolului�GH�DSOLFD LL�SHQWUX�WHUPLVWRDUHOH�17&VH�SRW�DSOLFD�úL�vQ�FD]XO�WHUPLVWRDUHORU�37&��R�FODVLILFDUH�XQLWDU��D�DSOLFD LLORU�ILLQGGHVWXO�GH�GLILFLO�GH�UHDOL]DW��3HQWUX�XQLWDWHD�SUH]HQW�ULL�YRP�XWLOL]D�DFHHDúL�FODVLILFDUHúL�YRP�vPS�U L�DSOLFD LLOH�GXS��UHJLPXO�GH�OXFUX�DO�WHUPLVWRDUHORU�37&��vQ�UHJLP�GHvQF�O]LUH�LQGLUHFW��VDX�vQ�UHJLP�GH�vQF�O]LUH�GLUHFW��

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    8Q�H[HPSOX�GH�DSOLFD LH�HVWH�SUH]HQWDW�vQ�ILJXUD�2.118.Montajul din figura 2.118 este un circuit comparator. La temperaturi T

  • Cap.2 Rezistoare

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    R2

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    'LQ� DFHHDúL� FDWHJRULH�GH� DSOLFD LL� IDFH� SDUWH� úL� H[HPSOXO� XUP�WRU�� UHJODUHDWHPSHUDWXULL�OD�PDúLQD�GH�VS�ODW�DXWRPDW��

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    TN2(60°C)

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    θ(°C)

    Fig. 2.120 Utilizarea termistoarelor PTC la reglarea temperaturii.

  • &RPSRQHQWH�úL�FLUFXLWH�SDVLYH Note de curs

    3

    În acest ciUFXLW� UH]LVWHQ D� GH� VDUFLQ�� 5L� VH� DIO�� vQ� FXSODM� WHUPLF� VWUkQV� FXtermistoarele PTC RT1-RT3, fiecare corespunzând unei temperaturi prestabilite careWUHEXLH� UHJODW���(OHPHQWXO� GH� FRQWURO� DO� FXUHQWXOXL� SULQ� UH]LVWHQ D� GH� VDUFLQ�� HVWHtriacul T1�� /D� R� DQDOL]�� VLPSOLILFDW�� SXWHP� FRQVLGHUD� WULDFXO� FD� XQ� FRPXWDWRUcaracterizat prin parametrul tensiune de prag Up. Atât timp cât tensiunea deFRPDQG��8c este mai mare ca Up triacul conduce curentul electric. În caz contrarWULDFXO�HVWH�EORFDW��DYkQG�R�UH]LVWHQ ��SUDFWLF�LQILQLW���5ROXO�WHUPLVWRDUHORU�HVWH�GH�DVHVL]D� FUHúWHUHD� WHPSHUDWXULL� úL� D� FRPDQGD� EORFDUHD� WULDFXOXL�� OD� R� DQXPLW�

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  • Cap.2 Rezistoare

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    3ULQ�GHILQL LH�SXWHUHD�HOHFWULF��LQMHFWDW��vQ�WHUPLVWRU�HVWH�3 5,2 , unde R esteUH]LVWHQ D� WHUPLVWRUXOXL� vQDLQWH�GH�EDVFXODUH�� OD� WHPSHUDWXUD� DPELDQW��7a. PutereaGLVLSDW��GH�WHUPLVWRU�HVWH�3 '�7b-Ta) unde Tb este temperatura de basculare iar TaHVWH� WHPSHUDWXUD� DPELDQW�� úL� '� HVWH� FRHILFLHQWXO� GH� GLVLSD LH� DO� WHUPLVWRUXOXL�5HXQLQG� FHOH� GRX�� UHOD LL� VH� RE LQH� 5,2=D(Tb-Ta��� UHOD LH� YDODELO�� SHQWUXtemperaturi ambiante mai mici sau egale cu Tb.

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    La aplicarea unei tensiuni de alimentare UA circuitului serie din figura 2.121echilibrul se atinge în punctul M1, la un curent relativ ridicat. Echilibrul seVWDELOHúWH�vQ�SXQFWXO�03�QXPDL�GDF��YkUIXO�%�DO�FDUDFWHULVWLFLL�,�8��D�WHUPLVWRUXOXLVH�VLWXHD]��VXE�GUHDSWD�GH�VDUFLQ���$FHVW�OXFUX�VH�SRDWH�vQWkPSOD�vQ�WUHL�VLWXD LL����UA FUHúWH�� ��� WHPSHUDWXUD� DPELDQW�� FUHúWH�� ��� UH]LVWHQ D� GH� VDUFLQ�� VFDGH�� 3ULQstabilirea echilibrului în punctul M3 VH� H[SOLF�� úL� SURWHF LD� UHDOL]DW�� GHtermistoarele PTC.

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    ′ (vezi figura 2.122) la punctul M1�SULQ�FRERUkUHD�GUHSWHL�GH�VDUFLQ�VXE�SRU LXQHD�FXUEDW��D�FDUDFWHULVWLFLL�WHUPLVWRUXOXL��$FHVW�OXFUX�VH�SRDWH�vQWkPSODGDF��WHQVLXQHD�GH�DOLPHQWDUH�VFDGH��OD�PHQ LQHUHD�FRQVWDQW��D�VDUFLQLL��YH]L�ILJXUD2.126��D���VDX�GDF��YDORDUHD�UH]LVWHQ HL�GH�VDUFLQ��FUHúWH��OD�WHQVLXQH�GH�DOLPHQWDUHFRQVWDQW���FD�vQ�ILJXUD�2.126 (b).

    'H�DLFL�UH]XOW��úL�RSHUD LLOH�SUDFWLFH�FDUH�VH�IDF�vQ�FD]XO�vQ�FDUH�R�SURWHF LH�FXWHUPLVWRU� 37&� vQ� VHULH� D� IRVW� DFWLYDW��� 'H� FHOH�PDL� PXOWH� RUL�� vQV��� vQWUHUXSHUHDWHQVLXQLL�GH�DOLPHQWDUH�HVWH�VLQJXUD�YDULDQW��SRVLELO��

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    (a) (b)Fig. 2.126 “Resetarea” termistorului PTC (a) prin reducerea tensiunii de alimentare;

    ��E��SULQ�FUHúWHUHD�UH]LVWHQ HL�GH�VDUFLQ��

    'LQWUH� PXOWLSOHOH� GRPHQLL� GH� DSOLFD LH� FDUH� XWLOL]HD]�� SURWHF LD� FXtermistoare PTC conectate în serie, amintim:

    • WUDQVIRUPDWRDUH�úL�PRWRDUH�HOHFWULFH�• surse de alimentare;• difuzoare;• VLVWHPH�GH�LOXPLQDUH�IOXRUHVFHQW��• vQF�O]LWRDUH�úL�ERLOHUH��PDúLQL�GH�VS�ODW�• OLQLL�GH�WHOHFRPXQLFD LL��FHQWUDOH�WHOHIRQLFH�• linii de transmisiuni de date (ISDN);• porturi ale calculatoarelor (USB, video, mouse, tastaturi, SCSI).

    Exemplu. 6H� YD� H[HPSOLILFD� FX� DFHHDúL� DSOLFD LH� SUH]HQWDW�� vQ� FXOHJHUHD� GH� SUREOHPH� >�@Problema 3.2.9 pag 76.

    S�� VH� DOHDJ�� XQ� WHUPLVWRU� 37&�� GLQ� JDPD� 3KLOLSV� ����� ��������� PRGHO� 37&� ��� FXtemperatura de basculare Tb=140°&��FDUH�V��SURWHMH]H�XQ�GLIX]RU�DOLPHQWDW�GH�OD�XQ�DPSOLILFDWRUDXGLR�GDF��

    temperatura de lucru este Ta=25°C;curentul normal de lucru I≤0,5A;WHQVLXQHD�PD[LP��GH�OXFUX�8a=20V;FXUHQWXO�GH�VXSUDVDUFLQ��PD[LP�,M=10A.

    Datele electrice ale termistoarelor PTC 30 sunt prezentate în Tabelul 2.18.Deoarece Vmax≥UA�� UH]XOW�� F�� WHUPLVWRDUHOH� GLQ� DFHDVW�� FDWHJRULH� FRUHVSXQG�� OD� SULPD

    H[DPLQDUH��FHULQ HORU�6H�YD�DOHJH�XQ�WHUPLVWRU�FDUH�vQGHSOLQHúWH�PLQLPDO�FRQGL LLOH� ,nc≥I (Int non trip în limba

    HQJOH]���vQ�WDEHO��úL�,max≥IM��&RUHVSXQGH�FRQGL LHL�WHUPLVWRUXOXL���������������FX�525=1,1Ω.

  • Cap.2 Rezistoare

    8

    Tabelul 2.18 Date de catalog pentru termistoarele Philips 2322 66.4/5/6 model PTC 30, [33].

    Conform figurii 2.123, în cazul unei supratensiuni echilibrul se va stabili în punctul M3′,

    OD�XQ�FXUHQW� DSUR[LPDWLY� HJDO� FX� FHO� UH]LGXDO�� 6H� SRDWH� FDOFXOD� úL� WLPSXO� QHFHVDU� FRPXW�ULL� SHbaza graficului din figura 2.127��FXUED�QU����$VWIHO��VH�FDOFXOHD]��UDSRUWXO�,M/Inc= 10/0.83 ≅���úLGLQ�ILJXU��UH]XOW��WLPSXO�GH�FRPXWDUH�Wb= 0,6 s.

    Fig. 2.127 Timpul de comutare al termistoarelor PTC Philips 2322 66.4/5/6, [33].

    7UHEXLH�I�FXW��UHPDUFD�F��YDORULOH�FXUHQ LORU�GH�FRPXWDUH�QRQ�FRPXWDUH�GHSLQG�GH�WHPSHUDWXU��ca în figura 2.128.

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    $VWIHO�� GDF�� WHPSHUDWXUD� DPELDQW�� HVWH� GLIHULW�� GH� ��°&� VH� YD� LQH� VHDPD� GH� JUDILFHOHprezentate.

    Fig. 2.128�9DULD LD�FX�WHPSHUDWXUD�D�FXUHQ LORU�,F��,t), Inc (Int), Imax pentru termistoarele PTCPhilips 2322 66.4/5/6, [33].

    2 (b) Demagnetizarea tuburilor cinescop colorDe foarte mult timp demagnetizarea tuburilor cinescop a fost una din

    DSOLFD LLOH�LPSRUWDQWH�SHQWUX�WHUPLVWRDUHOH�37&�� LQkQG�VHDPD�GH�QXP�UXO�PDUH�GHreceptoare de televiziune sau monitoare care se produc.

    7XEXULOH�FLQHVFRS�FRORU�SRVHG��vQ�VSDWHOH�HFUDQXOXL�R�PDVF��SHUIRUDW���FDUHHVWH� UHDOL]DW�� GH� RELFHL� GLQ� PHWDOH� FDUH� VH� SRW� PDJQHWL]D� IRDUWH� XúRU� �PDWHULDOHPDJQHWLFH� PRL��� 0DJQHWL]DUHD� P�úWLL� SHUIRUDWH� SRDWH� IL� SURGXV�� GH� FkPSXULPDJQHWLFH� H[WHUQH� FXP� DU� IL� PDJQH LL� SHUPDQHQ L� DL� GLIX]RDUHORU�� ERELQH�HOHFWURPDJQH L� VDX� FKLDU� GH� FkPSXO�PDJQHWLF� WHUHVWUX��&D� XUPDUH� D�PDJQHWL] �ULLP�úWLL� SHUIRUDWH�� FDOLWDWHD� LPDJLQLL� VH� vQU�XW� HúWH� FXORULOH� QHPDLILLQG� SXUH� VDXDYkQG�ORF�LUL]D LL�GH�FXORDUH��'LQ�DFHVW�PRWLY�WRDWH�UHFHSWRDUHOH�GH�WHOHYL]LXQH�VDXPRQLWRDUHOH� FRORU� VXQW� SUHY�]XWH� FX� R� ERELQ�� GH� GHPDJQHWL]DUH� SODVDW�� vQ� MXUXOWXEXOXL�FLQHVFRS��3ULQFLSLXO�GH�GHPDJQHWL]DUH���GHJDXVVLQJ����vQ�HQJOH] ���FRQVW��vQVXSXQHUHD�P�úWLL�SHUIRUDWH�OD�XQ�FkPS�PDJQHWLF�DYkQG�LQL LDO�R�DPSOLWXGLQH�PDUH�GDU� GHVFUHVF�WRDUH� vQ� WLPS�� &D� XUPDUH�� PDWHULDOXO� GLQ� FDUH� HVWH� UHDOL]DW �� PDVFDSDUFXUJH� FLFOXUL� GH� KLVWHUH]LV� FX� DPSOLWXGLQH� GHVFUHVF �WRDUH�� LDU� PDJQHWL]DUHDUHPDQHQW��HVWH�DGXV��OD�R�YDORDUH�FRQYHQDELO�GH�VF�]XW��

    'H� RELFHL�� ERELQD� GH� GHPDJQHWL]DUH� HVWH� DOLPHQWDW �� GLUHFW� GH� OD� WHQVLXQHDDOWHUQDWLY�� D� UH HOHL� GH� ���9�� &XUHQWXO� SULQ� ERELQ�� WUHEXLH� V�� DLE�� LQL LDO� RDPSOLWXGLQH� GH� FLUFD� �$�� LDU� GXS�� FLUFD� XQ�PLQXW� YDORDUHD� FXUHQWXOXL� WUHEXLH� V �VFDG��VXE�,res = 2mA (vezi figura 2.130).

  • Cap.2 Rezistoare

    10

    Fig. 2.129�3ULQFLSLXO�UHDOL]�ULL�GHPDJQHWL]�ULL�

    $FHVW�OXFUX�HVWH�QHFHVDU�SHQWUX�FD�LPDJLQHD�V��QX�ILH�SHUWXUEDW��GH�FXUHQWXOUH]LGXDO��SULQ�ERELQD�GH�GHPDJQHWL]DUH��,GHDO�DU�IL�FD�ERELQD�GH�GHPDJQHWL]DUH�V �ILH� VFRDV�� FRPSOHW�GLQ�FLUFXLW�� vQV�� DFHVW� OXFUX�SUHVXSXQH�FRVWXUL�PDUL��2� VROX LHIRDUWH� EXQ�� úL� HFRQRPLF�� R� FRQVWLWXLH� XWLOL]DUHD� WHUPLVWRDUHORU� 37&� vQ� VHULH� FXbobina de demagnetizare.

    Fig. 2.130�(YROX LD�vQ�WLPS�D�FXUHQWXOXL�GH�GHPDJQHWL]DUH�

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    ([LVW��GRX��YDULDQWH�GH�UHDOL]DUH�D�GHPDJQHWL]�ULL�FX�WHUPLVWRDUH�37&��FX�XQWHUPLVWRU�37&�VDX�FX�GRX��WHUPLVWRDUH�

    La varianta cu un singur termistor se cRQHFWHD]��HIHFWLY�WHUPLVWRUXO�vQ�VHULHcu bobina de demagnetizare, vezi figura 2.131.

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    Fig. 2.131 Circuit de demagnetizare cu un singur termistor.

    /D� FRQHFWDUHD� DOLPHQW�ULL�� WHUPLVWRUXO� HVWH� UHFH� úL� DUH� UH]LVWHQ D� PLF��� 3HP�VXU�� FH� WHUPLVWRUXO� VH� vQF�O]HúWH�� FUHúWH� úL� UH]LVWHQ D� OXL�� FXUHQWXO� SULQ� FLUFXLWscade, ajungând la valoarea curentului rezidual IRes.

    Valoarea curentului rezidual IRes�SRDWH�V��SURGXF��GLVWRUVLRQ�UL�DOH�LPDJLQLL�EUXP�� vQ� VSHFLDO� OD� UHFHSWRDUHOH� 79� FX� GLDJRQDO�� PDUH�� 'LQ� DFHVW� PRWLY� VHXWLOL]HD]��PRQWDMXO�FX�GRX��WHUPLVWRDUH�37&��OD�FDUH�XQXO�GLQ�WHUPLVWRDUH�DUH�UROXOGH� HOHPHQW� GH� vQF�O]LUH�� 'LQ� ILJXUD� ������ VH� REVHUY�� F��� RGDW�� FX� FUHúWHUHDWHPSHUDWXULL� DPELDQWH� DUH� ORF� úL� VF�GHUHD� YDORULL� FXUHQWXOXL� UH]LGXDO�� 5ROXO� FHOXLGH�DO� GRLOHD� WHUPLVWRU� HVWH� WRFPDL� GH� D� DVLJXUD� R� WHPSHUDWXU�� ULGLFDW�� SHQWUXWHUPLVWRUXO�DIODW� vQ�VHULH�FX�ERELQD�GH�GHPDJQHWL]DUH��6H�XWLOL]HD]��GRX��YDULDQWHde conectare, prezentate în figura 2.132.

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    Fig. 2.132 &LUFXLWH�GH�GHPDJQHWL]DUH�FX�GRX��WHUPLVWRDUH�

    La varianta din figura 2.132� �D��� FHOH� GRX�� WHUPLVWRDUH� VH� DIO�� vQ� VHULH� FXbobina de demagnetizare Ld��'XS��XQ�DQXPLW�WLPS�GH�OD�FRQHFWDUH��WHUPLVWRUXO�5T1SUHLD� UROXO�XQXL� UH]LVWRU�GH� vQF�O]LUH�SHQWUX� WHUPLVWRUXO�5T2��5H]LVWRUXO�5� DVLJXU�pentru RT1� XQ� FXUHQW� FDUH� vO� PHQ LQH� OD� R� WHPSHUDWXU�� ULGLFDW��� &HOH� GRX�

  • Cap.2 Rezistoare

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    WHUPLVWRDUH�VXQW�UHDOL]DWH�vQ�DFHHDúL�XQLWDWH�FRQVWUXFWLY���vQ�DúD�IHO�vQFkW�vQWUH�HOH�V�existe un cuplaj termic bun.

    La montajul din figura 2.132 (b) este eliminat rezistorul auxiliar R,IXQF LRQDUHD�FLUFXLWXOXL�ILLQG�VLPLODU���ÌQ�ILJXUD�2.133�VH�REVHUY��F���vQ�OLSVD�OXL�5T1YDORDUHD� UH]LVWHQ HL� OXL� 5T2 corespunde punctului M1� LDU� vQ� SUH]HQ D� OXL� 5T1punctului M2, asigurând astfel un curent mai mic prin circuit. De asemenea, seREVHUY��F��FHOH�GRX��WHUPLVWRDUH�DX�FDUDFWHULVWLFL�GLIHULWH�

    R(log)

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    Fig. 2.133 Caracteristicile termistoarelor utilizate la demagnetizare.

    'LQ� SXQFW� GH� YHGHUH� FRQVWUXFWLY� FHOH� GRX�� WHUPLVWRDUH� VXQW� UHDOL]DWH� VXEIRUP��GH�GLVFXUL�FRQHFWDWH� vQ� DFHHDúL� FDUFDV��� FRPSRQHQWD� ILLQG�XQ�GLVSR]LWLY� FXtrei terminale, ca în figura 2.134.

    Termistoaredisc

    lamelearcuite

    Fig. 2.134�&RQVWUXF LD�GLVSR]LWLYXOXL�FX�GRX��WHUPLVWRDUH�XWLOL]DW�OD�GHPDJQHWL]DUH�

    ���F��7HUPLVWRDUH�37&�SHQWUX�SURWHF LD�YROWPHWUHORU�GLJLWDOH��'00�'LIHUHQ D�SULQFLSDO��vQWUH�WHUPLVWRDUHOH�SHQWUX�SURWHF LD�YROWPHWUHORU�GLJLWDOH

    úL� WHUPLVWRDUHOH� XWLOL]DWH� vQ� JHQHUDO� OD� SURWHF LH� HVWH� YDORDUHD� IRDUWH� UHGXV�� DFXUHQ LORU�GH�QRQ�FRPXWDUH�,nc, respectiv de comutare Ic. În acest caz, la o tensiuneH[FHVLY�� DSOLFDW�� OD� ERUQH� WHUPLVWRUXO� YD� DF LRQD� IRDUWH� UDSLG�� SURWHMkQG� DVWIHOcircuitul, vezi figura 2.135.

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    Fig. 2.135 8WLOL]DUHD�WHUPLVWRDUHORU�37&�OD�SURWHF LD�YROWPHWUHORU�HOHFWURQLFH�

    Curentul de comutare Ic�SHQWUX�DFHVWH�WHUPLVWRDUH�DUH�YDORDUHD�FXSULQV��vQWUH�����P$�� 5H]LVWHQ �� LQL LDO�� 5T25� HVWH� FXSULQV�� vQWUH� VXWH� GH� RKPL� úL� XQLW� L� GHNLORRKPL�� FUHVFkQG� SXWHUQLF� SkQ�� OD� ��·���� 0Ω. Valoarea relativ mare aUH]LVWHQ HL� LQL LDOH� QX� HVWH� VXS�U�WRDUH� GHRDUHFH� FLUFXLWXO� GH� LQWUDUH� SUH]LQW�LPSHGDQ H�FX�YDORUL�PDUL�

    2 (d) Termistoare PTC pentru pornirea motoarelor electrice.$FHVWH�WHUPLVWRDUH�VXQW�XWLOL]DWH�vQ�FRQH[LXQH�VHULH�FX�vQI �úXUDUHD�GH�SRUQLUH

    a motoarelor electrice. La pornirea motoarelor (de ex. motoare de frigider sau aleLQVWDOD LLORU�GH�DHU�FRQGL LRQDW��FXUHQWXO�QHFHVDU�vQ�vQI�úXUDUHD�DX[LOLDU��GH�SRUQLUHHVWH�UHODWLY�PDUH��GXS��SRUQLUH�DFHVW�FXUHQW�QHPDLILLQG�QHFHVDU��7HUPLVWRUXO�37&SRDWH�FX�VXFFHV�V��vQGHSOLQHDVF��DFHVWH�FHULQ H�DGLF��V��DVLJXUH�OD�SRUQLUH�XQ�FXUHQWLPSRUWDQW� LDU� GXS�� SRUQLUH� V�� VFRDW�� SUDFWLF� GLQ� FLUFXLW� vQI�úXUDUHD� DX[LOLDU��&RQHFWDUHD�WHUPLVWRUXOXL�SRDWH�IL�XUP�ULW��vQ�VFKHPD�GLQ�ILJXUD�2.136.

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    Fig. 2.136 Utilizarea termistoarelor PTC la pornirea motoarelor electrice.

  • Cap.2 Rezistoare

    14

    ���H��&LUFXLWH�GH�vQF�O]LUH�WHUPRVWDWDWH7HUPLVWRDUHOH� 37&�SRW� IL� XWLOL]DWH� FD� HOHPHQWH� GH� vQF�O]LUH� SHQWUX� OLFKLGH�

    aer sau mai nou pentru oglinzile automobilelor.$YDQWDMXO� WHUPLVWRDUHORU� ID �� GH� HOHPHQWHOH� UH]LVWLYH� FODVLFH� HVWH� IDSWXO� F�� SULQXWLOL]DUHD� ORU� VH� UHDOL]HD]�� VLPXOWDQ� úL� WHUPRVWDWDUHD� RELHFWXOXL� vQF�O]LW�� $VWIHO�GXS�� FH� WHPSHUDWXUD� GH� EDVFXODUH� D� IRVW� DWLQV��� WHUPLVWRUXO� GLVLS�� PDL� SX LQ�F�OGXU��� UH]LVWHQ D�FUHVFkQG�SXWHUQLF��7HUPLVWRUXO�HVWH�XWLOL]DW� vQ�DFHVW�FLUFXLW�DWkWFD�HOHPHQW�GLVLSDWLY�GDU�úL�FD�HOHPHQW�UHJXODWRU��YH]L�ILJXUD�2.137.

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    Fig. 2.137 8WLOL]DUHD�WHUPLVWRDUHORU�37&�FD�HOHPHQW�GH�vQF�O]LUH�FX�WHPSHUDWXU��FRQWURODW��

    2 (f) Indicatoare de nivelUtilizarea termistoarelor PTC în circuite de sesizare (indicare) a nivelului

    IOXLGHORU� VH� ED]HD]�� SH� DFHODúL� SULQFLSLX� SUH]HQWDW� OD� DSOLFD LLOH� VLPLODUH� FXWHUPLVWRDUHOH� 17&� úL� DQXPH� SH� IDSWXO� F�� vQ� OLFKLG� FRHILFLHQWXO� GH� GLVLSD LH� DOtermistoarelor este mai mare ca în aer. În cazul termistoarelor PTC, curentul deIXQF LRQDUH�FDUH�VH�VWDELOHúWH�SULQ�WHUPLVWRU�HVWH�PDL�PDUH�DWXQFL�FkQG�WHUPLVWRUXO�HVWHLPHUVDW� vQ� OLFKLG� ID �� GH� VLWXD LD� FkQG� GLVLS�� vQ� DHU�� ÌQ� PRG� HFKLYDOHQW�� UH]LVWHQ DWHUPLVWRUXOXL� LPHUVDW� vQ� OLFKLG� HVWH� PDL� PLF��� ÌQ� ILJXUD� 2.138 a fost prezentat unLQGLFDWRU� GH� QLYHO� FX�PDL�PXOWH� WHUPLVWRDUH� 37&� SODVDWH� SH� YHUWLFDO�� vQ� IOXLGXO� DOF�UXL�QLYHO�VH�P�VRDU���&XUHQWXO�SULQ�FLUFXLW�HVWH�R�LQGLFD LH�D�QLYHOXOXL�IOXLGXOXL�

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    Fig. 2.138 Utilizarea termistoarelor PTC în indicatoare de nivel a lichidelor.

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    Când un termistor PTC este conectat în serie cu bobina unui releu, releulHVWH� DQFODQúDW� �DF LRQDW�� LPHGLDW� GXS�� FRQHFWDUHD� WHQVLXQLL�� XUPkQG� V�� ILHGH]DFWLYDW�GXS��XQ�WLPS��WLPS�vQ�FDUH�WHUPLVWRUXO�VH�vQF�O]HúWH�

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    (a) (b)Fig. 2.139��D��5HDOL]DUHD�XQHL�WHPSRUL]�UL���E��HYROX LD�vQ�WLPS�D�FXUHQWXOXL�

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    'DF��WHUPLVWRUXO�VH�FRQHFWHD]��vQ�SDUDOHO�FX�UHOHXO��DQFODQúDUHD�DUH�ORF�GXS�XQ�WLPS��WLPS�QHFHVDU�WHUPLVWRUXOXL�SHQWUX�D�VH�vQF�O]L�

    ���K��6XUV��GH�FXUHQW�FRQVWDQW&RQHFWkQG�XQ�WHUPLVWRU�37&�vQ�SDUDOHO�FX�XQ�UH]LVWRU�HVWH�SRVLELO�V��VH�DVLJXUH�SULQUH]LVWRUXO�GH�VDUFLQ��5V�XQ�FXUHQW�DSUR[LPDWLY�FRQVWDQW�

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