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"/&"0 y ?? wfqwo  b"@ wwt |<88<8?  ~y#fff` xf` yf` <<>99` 9 0f <8>x<@ p 9y `faf`~yxcf`y@fc99 <c``??  `? |G  G@?~|@0 ?7pwȏ<?p???b"","  ? ? wvwo@@><  #ݙݿ9ٝ?#|"f""@ | b&b"$#~#p@;;@#wCgw?>?t6ws#qqHɈ#~y#@;;@#ݙݿy9ٜ]?#|"f:"@ | b&c$??<   wvwo@@  ? ? ???b"","?p7pwȏ<? 0@?~|G@ G ? |   @~@0 xxxx x#xwwtx0x 03xb"@>3 x 30wfwwox33x??8333???x"/&"03> yx ?? wfqwox x x0 3xb"@   x 03 >3wwt x x03 3303 x 03 ?303  3x# 03 030 x x 3 xx ?x   x 8 x >>> x 3 3030 x ? ?0033 x 0 00033 x 03>xxxxxGINF ;'DvTABL~;'Dddddd SoftSans dSoftSans dSoftSans dSoftSans dSoftSans dvTCLS>W+}>W+}>W+~>W+~n>W+6>WgB3>W+]W+^XW+^WW$nWWj3WW‚WW&WnW>W3WVCELLRULEBATTR  dCHRS Material TypATTR dCHRSeATTR dCHRS:CLLECELLRULE??ATTR dCHRSImpurity type:CLLECELLRULE-$ATTR dCHRSElement used:CLLECELLRULEATTR dCHRSValency Electrn.:CLLECELLRULEH?ATTR dCHRSElectric flow due to:CLLECELLRULEATTR dCHRSFlow of current:CLLECELLRULE6-ATTR dCHRSImpurities referred to:CLLECELLRULEATTR dCHRSN-TypeCLLECELLRULE ,ATTR dCHRS ATTR dCHRS Penta-valentCLLECELLRULE ,ATTR dCHRS ATTR dCHRS PhosphorusCLLECELLRULE,ATTR dCHRS ATTR dCHRS5CLLECELLRULE,ATTR dCHRS ATTR dCHRSextra electronsCLLECELLRULE ,ATTR dCHRS ATTR dCHRS -ve to +veCLLECELLRULE BATTR dCHRS ATTR dCHRS Donor ImpATTR dCHRS.CLLECELLRULEATTR dCHRSP-TypeCLLECELLRULE ,ATTR dCHRS ATTR dCHRS Tri-valentCLLECELLRULE ATTR dCHRS AluminiumCLLECELLRULEATTR dCHRS 3CLLECELLRULEATTR dCHRS holes (lack of electrons)CLLECELLRULE ,ATTR dCHRS ATTR dCHRS +ve to -veCLLECELLRULE,ATTR dCHRS ATTR dCHRS Acceptor Imp.CLLEGINFUtils:APPLICATIONS/PPaint/Brushes/FWriter5/Diodes.bshN N _-29BlackFORMILBMBMHD1 D,CMAP @@CAMGBODY00??~?~??0 ~?? @ 0P0` ||c? s8<|@c 00`  ||co? s<f@s 0` ||c? sf@{ 0P` ` ||c s8|@o0?  ||co?  s8`@g 0` ||c? s8`@c 0P`  ||c? s8`@c 0p`  ` ||co? s8<@ 0` ||c? s8<? ~?  `t[9r txvZ &)ƿZ@Q9@@%)⭜(޿bRc!@$)ޭk[޿~z!R!@$) [އ}{9R!xt{cTƧ{9XdGINFUtils:APPLICATIONS/PPaint/Brushes/FWriter5/DiodesExample1.bshNN2,q9BlackFORMILBMBMHD1P@h,CMAP @@CAMGBODY 000088'`8p|8x?s8~?s8~|8x'`8p88  Y}g&q 9َ VkZk JBR V=kB-k K”VjkJ! }iql &9  @??L6gf?833f?ZֻZ$)DJPI Dx?[>Z $ DzPIP0?[ֻZ.0`!)DBPIP??9ͷf@9D2H&@ DdD``qp?DFDP?`q @`@;0`FE 08?GINFUtils:APPLICATIONS/PPaint/Brushes/FWriter5/Line2.bshMXRMXRq6d9BlackFORMTILBMBMHD& D,CMAP0f"@@CAMGBODY<U߻TU߻TU߻Twww<GINF SHD1PWWLWPTMainTBDYRULEJATTR dCHRSElectronic Servicing yr.1 pt.1ATTR dCHRS ATTR hdCHRS ATTR hdCHRS ATTR hdCHRS ATTR dCHRS Lecture: 005 ATTR [dCHRS ATTR hdCHRS ATTR hdCHRS ATTR hdCHRS ATTR hdCHRS Wed-23-OctoberATTR hdCHRS-1996RULEATTR hdCHRSRULE &ATTR& xCHRS&The history of electrical current flowRULE ATTR dCHRSRULE {,ATTRY dCHRSYIn the early days of electricity, it was decided that current flows in a circuit from the Positive source to the Negative source. By that time very little was known about electric current flow. Linked with this theory, many other theories were based on, especially those which include electro-magnetism. Today this old theory is referred to the ATTR" dCHRS" conventional current flow theory.RULE ATTR dCHRSRULE 9XATTR dCHRSIn 1905 with the invention of the thermionic diode valve, it was shown and concluded that current is a flow of electrons from the negative to the positive terminal. This became known as theATTR dCHRS ATTR dCHRSelectron current flow theory.ATTR^ dCHRS^ This theory is used to explain electronic circuits and some parts of the transistor circuits.RULE ATTR dCHRSRULE gJATTR dCHRSWith the invention of the transistor (1947) a new theory about current flow was discovered. It was brought forward that a transistor is made up of two types of materials, the ATTR dCHRSn-typeATTR dCHRS and the ATTR dCHRSp-typeATTR dCHRS materials. TheATTR dCHRS N-TypeATTR dCHRS material is negatively induced material since there is a surplus (extra) electrons in the crystal structure. These electrons are called ATTR dCHRSdonor electronsATTR dCHRS. ATTR dCHRSTheATTR dCHRS P-TypeATTRe dCHRSe material is positively induced material since there is lack of electrons, or what they are called ATTR" dCHRS"holes, i.e. - acceptor electrons.ATTRG dCHRSG Electricity flows from the N-type material from the -ve to the +ve due the flow of the extra electrons, whereas in the P-type it flows in the opposite direction due the the flow of holes (lack of electrons). Hence the latter has the same direction of conventional current flow (from +ve to -ve) but is it is referred as the ATTR dCHRShole current flow theory.RULE ATTR dCHRSRULE  ATTRdCHRSSemiconductors (Si / Ge)RULE nATTRn dCHRSnThere are only two semiconductor elements, hence Silicon (si) and Germanium (Ge). Since Germanium is rare and so expensive, Silicon, which is very abundant and cheap, is used. Silicon (or Germanium) is obtained from ores, and are first refined (purified) to the extent of 1 part per 1 billion (1:1,000,000,000). At this stage the semiconductor becomes an insulator. RULE ATTR dCHRSRULE ATTR dCHRSIf the refined Si/Ge is added a certain ammount of impurity, they will behave as a conductor, and back to an insulator by a simple electric impulse. This can be switched between conductor/insulater at high rates such as 1 million times per second. These elements have a valency of 4. The outermost shell of Ge/Si needs 4 other valence electrons to have a full orbit of 8 electrons. To perform this, a single Si atom will share an electron with four other Si atoms adjecent to it, so it will have 8 electrons, as shown in the diagram.RULE ATTR dCHRSRULE sATTR dCHRSWhen a pentavalent impurity such as Phosphorus is added in the ratio of 1 atom per 10 million Si atoms (1:10,000,000), Si will become an n-type conductor. It conducts electricity since Phosphorus provides an extra electron to the lattice, (P=5eATTR dCHRS-ATTR dCHRS s, Si= 4eATTR dCHRS-ATTR dCHRSs) and so there will be wandering electrons which results in flow of electrcity. This flow in the n-type material is the same as the electron current flow theory, hence from -ve to +ve. ATTRG dCHRSGTherefore in N-type, the flow of electrical current is from -ve to +ve ATTRs dCHRSsdue the flow of extra electrons provided by the penta-valent impurity - Phosphorus in the Silicon crystal lattice. RULE ATTR dCHRSRULE BATTR dCHRSIn a P-type material, a trivalent impurity such as Aluminium is added in the same ratio of 1 atom per 10 million Si atoms (1:10,000,000). This makes a positive empty space called a hole running in the Si crystal lattice. These holes are considered +ve since they are a defficiency (lack) of electrons, and in fact they can accept electrons like positve charges. These wandering holes provide flow of electricity in the P-type material, which flow from the positive to the negative - the same as the conventional current flow. ATTRG dCHRSGTherefore in P-type, the flow of electrical current is from +ve to -ve ATTRy dCHRSydue the flow of holes (lack of electrons) provided by the tri-valent impurity - Aluminium in the Silicon crystal lattice.RULE ATTR dCHRSN-type and P-Type material is used in Diodes. This is made up of a semiconductor bar, of which half is p-type and half is n-type material. The following symbols all represent diodes.RULE ATTR dCHRSRULE ATTR dCHRSRULE ATTR dCHRSRULE ATTR dCHRSRULE ATTR dCHRSRULE ATTR dCHRSThe arrowhead in the electronic symbol shows the flow of conventional current. Diodes ensure uni-polarity, as they allow current to pass from one direction only, hence from +ve to -ve. These are used in rectifiers to convert dc to ac.RULE ATTR dCHRSRULE ATTR dCHRSRULEATTR dCHRSRMSTRULEATTR dCHRSLMSTRULEATTR dCHRS