ELE641A-powe Electronics power point presentation.pptx

PPT on power electronics

1. GOOD MORNING TO ALL Welcome to Online Class Kindly mute your microphone & Video Waiting for others to join…… Use Chat box to communicate Class will start soon…….

2. ELE641A: Non-conventional Energy Sources and Power Electronics UNIT 1 : Energy Resources and Photovoltaic Systems( Hours:15) (HH) UNIT 11 : Wind, Geothermal and Piezo Electric Energy harvesting ( Hours:15)(HH) UNIT 111 : Power Electronics ( Hours: 15)(OVJ)

3. CIA 1: Discuss the application of Power electronics in Biomedical instrumentations : Date of submission : 27/01/23 Evaluation Rubric/s :  Written assignments will be evaluated out of 20 as per the following rubrics( Minimum Five pages) Contents Marks IEEE reference format 4 Content/Theory 4 Diagrams 4 Journal reference 4( minimum four) Applications 4(minimum five) Total 20

4. Power Electronics Introduction, study of power devices, power diode and power transistor, UJT, SCR, SCR as a half wave and full wave rectifier, power control using SCR. DIAC ,TRIAC, power MOSFET and IGBT, Applications-charge controllers with IGBT/MOSFET, Concept of UPS, types, offline and line interactive, functional block diagram, dc choppers, Inverters , Switched mode power supply (SMPS).

5. Power Electronics

6. Power Electronics Power electronics is one of the important branches of electronics and electrical engineering. It deals with the conversion and control of electrical energy. We know that AC voltage and current of fixed frequency available from the main supply. This supply cannot be used directly always. The figure shown above shows the basic functioning of the power electronic systems. The electric energy in one form is given at the input of the power electronic systems and it converts the energy into another form. For example, the input can be an AC and the output can be DC. We know that such a conversion is done by an rectifier. Hence rectifier can be considered as a power electronic system. The power electronic systems ,therefore performs the conversion of electronic energy. It also control the amount of energy given to the output.The word power means high amplitude current and voltages

7. Application of power Electronics Uninterruptible power supplies and stand by power supplies for critical load such as computers and medical equipment etc Power control in resistance welding induction heating, electrolysis, process industry etc Power conversion for HVDC and HVAC transmission system Speed control of motors which are used in traction drivers, textile mills, rolling mills, cranes, lifts, compressor, pumps , elevators , etc Solid state power compensators, static contactors, transformer tap changers etc High voltage supplies for electrostatics precipitators, and X ray generators Power supplies for communication systems, telephone exchanges and satellite systems etc

8. Advantages of power electronic controllers Fast dynamic response due to static device High efficiency of conversion due to low losses in electronic devices Increased operating life and reduced maintenance since there are no moving parts Power electronic controllers use digital or microprocessor-based control. Hence their operation is highly flexible. Since solid state device are used, electromagnetic interference and acoustic noise is reduced.

9. Draw back of power electronic controllers The power electronic controllers generate harmonics. These harmonics affect the performance of other loads The power factor of some power electronic controller is very low. Hence power factor correction is necessary to reduce reactive power For very simple conversion requirements, power electronic converters may be costly. Here note the advantages outweigh the disadvantages. Hence power electronic controllers are used in large number of applications

10. Power semiconductor devices Power semiconductor devices DIODES THYRISTORS TRANSISTORS General purpose SCR (Silicon controlled rectifier) BJT High speed GTO (Gate turn off thyristor) MOSFET Schottky RCT (Reverse conducting thyristor) IGBT   SITH (Static induction thyristor) SIT   GATT (Gate Assisted turn off thyristor)     LASCR (light activated silicon controlled rectifier)     MCT (Mos controlled thyristor)     TRIAC (Triode for alternating current)  

11. Semiconductor power diodes Power diodes are required in most of the power converters. Power diode is an un controlled device. When the anode (A) is positive with respect to cathode (K), the diode start conducting. Normally a forward bias of 1 volt is sufficient to push the diode in conduction mode. Current flows from anode to cathode.

12. Semiconductor power diodes The structure of the power diode is slightly different from small signal diodes. In this figure ,it is observed that there is a heavily doped n+ substrate with doping level of 10 19 /cm 3 . This substrate forms the cathode of the diode. On n+ substrate, lightly doped n - epitaxial layer is grown. This layer is called drift region. The doping level of n- layer is about 10 14 /cm 3 . Then a pn junction is formed by diffusing a heavily doped p+ region. This p+ region forms the anode of the diode. The doping level of the p+ region is about 10 19 /cm 3. The thickness of the p+ region is about 10µm and that of n+ substrate is about 250 µm. The thickness of the n- drift layer depends on the breakdown voltage of the diode. For higher breakdown voltages, the drift region is wide. The n- drift region is absent in low power signal diodes. The drift region absorbs the depletion layer of the reverse biased p + n - junction.

13. Types of power diodes General purpose diodes : These diodes have high reverse recovery time of the order of about 25µsec. Hence, these diodes are used in low speed applications such as rectifiers and converters. The can operate upto 1khz. Their current – voltage rating are 1A/50V to 1000A/500V . Application: Battery charging, electroplating, welding, UPS Fast recovery diodes : These diodes have reverse recovery time less than 5 µsec. Hence these diodes are used in high speed applications such as choppers and inverters, SMPS These diodes have rating from 1A/50V to 100A/3kV

14. Types of diodes Schottky diodes : In Schottky diode pn junction is eliminated. A thin layer of metal is placed directly on the semiconductor. Normally aluminium is deposited on n-type semiconductor. The metal is anode and semiconductor is cathode. Since there is no pn junction ,the storage time is absent. Hence turn of time is very small. Hence Schottky diodes have very high switching frequencies. The drift layer is absent.

15. Applications of power diodes Hence on state losses are very low. But Schottky diodes have large reverse leakage current. Their breakdown voltage capability is less than 100V. The Schottky diodes are used in low voltage converters as feedback and freewheeling diodes Applications of power diodes Power diodes are required in almost all power converters. Some of the applications are given below. Power diodes are used in un controlled rectifiers Feedback and freewheeling operation in choppers, inverters and controlled converters use power diodes Almost all the commutating circuits for SCR’s use power diodes Half controlled converters and half bridge inverters use power diodes

16. Thyristor Family There are eight types of power devices in thyristor family. They are 1.Silicon controlled rectifiers (SCR) 2.Gate turn off thyristor (GTO) 3.Reverse conducting thyristor (RCT) 4.Static induction thyristor (SITH) 5.Gate assisted turn off thyristor (GATT) 6Light activated silicon-controlled rectifier (LASCR) 7MOS controlled thyristor (MCT) 8TRIAC Out of all these devices, SCR is the most commonly used thyristor

17. POWER BJT The transistor family of the device consist of power BJT, MOSFETS, IGBT and SIT. These devices have fully controlled turn on and turn off behaviour. They do not need external commutation components. BJT, IGBT and MOSFETS are widely used in switched mode power supplies and PWM inverters. Due to the developments in manufacturing technology, it is possible to manufacture devices having high operating frequencies, low on state losses, and higher current /voltage rating

18. Structure of Power BJT

19. Structure of Power BJT The basic structure of power BJT is different from small signal transistors. The figure given below shows the vertical cross section of the power BJT. In the structure it is observed that there is a highly doped emitter region (10 19 per cm 3 ). The emitter region has the thickness of about 10µm. The base has the moderating doping of about 10 16 per cm 3 . Thickness of the base can vary from 5 to 20 µm. Small base thickness provide good amplification capabilities. But the breakdown voltage capability of the transistor is reduced for small base region. The collector is split in to two regions as shown in the diagram. These two regions are n-(10 14 per cm 3 ) and n+(10 19 per cm 3 ). The n- region has the light doping and it is called collector drift region. The thickness of the n- region determine breakdown voltage capability of the transistor. Thickness of this region is in the order of 50-200 µm. The n+ region has high doping density. This region serves as collector contact for external circuits. Thickness of this layer is in the order of 250 µm.

20. Steady state characteristics of BJT (Out put characteristics)

21. Steady state characteristics of BJT(Output characteristics) The VI characteristics of power BJT is shown below. These characteristics are also called output characteristics. The collector current Ic is plotted with respect to collector emitter voltage VcE For different values of base current I B. There are four regions in the graph. That is Cut-off region, Active region, quasi saturation and hard saturation region . The cut off region is area where the base current is almost zero. Hence no collector flows and transistor is in the off condition. In the quasi saturation and hard saturation, the base drive is applied and the transistor is in the ON state. Hence the collector flows depending upon the load. The BJT is never operated in the active region. It is operated in the cut off and saturation condition. Thus, BJT act as switch.

22. Steady state characteristics of BJT The BV SUS is the maximum collector to emitter voltage that can be sustained when BJT is carrying substantial collector current. BV CEO is the maximum collector to emitter breakdown voltage that can be sustained when the base current is zero, and BV CBO is the collector base breakdown voltage when the emitter is open circuited. Primary breakdown: The primary breakdown in BJT take place because of the avalanche breakdown of the collector base junction. The large power dissipation is normally leads to primary breakdown. Secondary breakdown. It clear from the above graph that, at larger collector current, the collector emitter voltage drops. Due to this drop in voltage the collector current increases. Here there is substantial increase in power dissipations. This power dissipation is not evenly spread across the entire volume of the device. But it is concentrated in the highly localized region In these region the local temperature grows very rapidly and BJT is damaged due secondary breakdown

23. Merits, Demerits & Applications of BJT Merits of BJT BJT have small turn on and turn off times, hence their switching frequencies are higher BJT have small turn on losses Base drive has full control over the operation of BJT BJT is a bipolar device BJT are available easily with much reduced cost Demerits of BJT Drive circuit of BJT is complex Storage charge in base reduces switching frequiences Negative temperature coefficients create problems in paralleling of BJT

24. Advantages of BJT Switched mode power supplies Bridge inverters DC to DC converters (Choppers) Power factor techniques Name of the device Volt-Current Rating Operating frequency BJT 2kV/ 1kA 10kHz MOSFET 1kV/50A 100kHz IGBT 1.5kV/400A 20kHz SIT 1.2kV/300A 100kHz

25. Unijunction Transistor (UJT)

26. Unijunction Transistor (UJT) UJT is a three terminal semiconductor switching device When the device is triggered ,the emitter current increases regeneratively until it is limited by emitter power supply It consist of n type silicon bar with electrical connection on each end These connections are to base B1 and base B2 A pn junction is formed between p type emitter and the bar The emitter E is near to base B2 The device has only pn junction and three leads With one junction ,the device is really a form of diode Two base terminals are taken from the one section of diode,it is called double based diode Emitter is heavily doped , n region is lightly doped

27. Working of UJT Figure a Figure b

28. Working of UJT Normally B2 is positive with respect to B1 If a voltage VBB is applied between B2 and B1 with emitter open ,a voltage gradient established along the n bar The emitter is near to B2. Hence more voltage gradient is between E and B1 This voltage V1 establish a reverse bias on PN junction and emitter current cut off If a proper positive voltage is applied to emitter E, it overcomes the negative reverse bias voltage and junction become forward biased

29. Working of UJT The holes injected from emitter are repelled by positive B2 and attracted towards B1, and there by emitter current IE increases As more holes are injected ,a condition of saturation will be reached ,At this point emitter current is limited by only emitter power supply. The device is said to be in ON state If a negative pulse is applied to E ,the junction become reverse bised and current cut off,The device is in OFF state

30. Equivalent Circuit of UJT

31. Equivalent Circuit of UJT The resistance of the silicon bar is called interbase resistance R BB It is represented by two resistance in series RB1 and RB2 The resistance RB1 is marked as variable ,because its value depend on biasing voltage The PN junction is replaced by diode D With no voltage applied to the UJT , the interbase resistance is given by the relation R BB = RB1 + RB2 If a voltage VBB is applied between the base with emitter open,the voltage will devide across RB1 and RB2 The voltage V1 across RB1 is equal to[ RB1/RB1+RB2] xVBB V1/VBB = RB1/RB1+RB2 = η = Intrinsic stand off ratio That is V1 = η VBB, this reverse bias the diode and current zero

32. Equivalent Circuit of UJT If a progressively rising + ve voltage is applied to the emitter ,the diode will become forward biased when the input voltage exceeds η VBB by VD The forward voltage across the silicon diode is Vp = η VBB + VD When the diode start conducting ,the holes are injected from p type to n type bar These holes are moving towards B1 The emitter current increase regeneratively until ,it is limited by emitter power supply

33. Characteristics of UJT

34. Characteristics of UJT Initially in the cut off region as VE increases from zero, leakage current flows from terminal B2 to emitter This current is due to minority charge carriers Above a certain value of VE, forward current IE begins to flow, increasing until the peak voltage VP and current IP reached at the point P After the peak point P, an attempt to increase VE, causes ,the sudden increase in IE and corresponding decrease in VE.This is a negative resistance region of the curve This – ve portion of the curve last until a vally point V is reached and the corresponding voltage Vv and the current Iv. After the vally point ,the device is in saturation condition

35. UJT application & Advantage UJT Typical applications: Used in oscillators Used in pulse and voltage sensing circuits Used in triggering circuits Used in saw tooth generation circuits Advantages of UJT It is a low-cost device It has an excellent characteristic It is a low power absorbing device under normal condition

36. DIAC A diac is a two terminal, three-layer bidirectional device which can be switched from its OFF state to ON state for either polarity of applied voltages. The diac can be constructed in either npn or pnp forms. The above figure shows the basic construction of pnp form. Two leads are connected to p region of the silicon separated by n region. The structure of the diac is very much similar to that of a transistor. However, there are some differences. There is no terminal attached to the base The three regions are nearly identical in size The doping concentration are identical to give symmetrical properties

37. Working of DIAC When a positive or negative voltage are applied across the terminals of the diac, only a small leakage current I BO will flow through device. As the applied voltage is increased ,the leakage current will continue to flow until the voltage reaches the breakover voltage V BO . At this point avalanche breakdown of the reverse biased junction occurs and the device exhibits a negative resistance ie current through the device increases with decreases the value of the applied voltages. The voltage across the device then drops to break back voltages Vw . The V I characteristics of a diac is shown below. For applied positive voltage less than +V BO and negative voltage less than -V BO , a small leakage current ± I BO flows through the device. Under such condition ,the diac blocks the flow of current and effectively behaves an open circuits.

38. DIAC characteristics Application: The Diac are used primarily for triggering of TRIAC in adjustable phase control of ac main power. Some of the circuit applications of Diac are light dimming, heat control, Universal motor speed control

39. Name the Device??

40. Silicon Controlled Rectifier (SCR) When a PN junction is added to a junction transistor, the resulting three PN junction device is called SCR. It is clear that it is essentially an ordinary rectifier(PN) and a junction transistor(NPN)combined in to one unit to form a PNPN device. One terminal is taken from outer P material called anode(A) ,second from outer N material called cathode( K),and third from the base of the transistor section called gate (G).

41. Structure of SCR

42. Working of SCR ( When the gate is Open) The figure given above shows the SCR circuit with gate open, that is no voltage applied to the gate. Under this condition J2 is reversed while the junction J1 and J3 are forward biased. Hence the situation in the junction J1 and J3 are just in an NPN transistor with gate open.No current flows through the load RL and SCR is cut off If the applied voltage is gradually increased a stage is reached where the reverse biased junction J2 brakes down.The SCR now conducts heavily and said to be in the ON state.The applied voltage at which SCR conducts heavily with out gate voltage is called breakover voltage.

43. Working of SCR ( When the gate is with + Ve voltage) A small positive voltage to the gate as shown in the diagram. Now the junction J3 is forward biased and junction J2 reverse biased. The electron from n type material starts flowing across the junction J3 towards the left where as the holes from P type materials towards right. As a result the electron from the junction J3 are attracted towards the junction J2.and gate current starts flowing. As soon as the gate current flows the anode current increases. The increased anode current in turn makes more electron available at the junction J2. This process continues and with in small time the junction J2 breakdown and SCR starts conducting heavily

44. The equivalent circuit of SCR :

45. The equivalent circuit of SCR

46. Working of SCR The transistor equivalent circuit of SCR is given below. It consist of an npn and pnp transistor connected as shown in the diagram. The collector of each transistor is coupled to the base of the other ,making a positive feedback loop. Assume that the supply voltage V is less than the breakover voltage. With gate open (switch S open ),there is no base current in the transistor T2.There fore no current flows in the collector of T2 and hence that of T1.Under such condition SCR is open If the switch S is closed, a small gate current will flow through the base of T2 which means its collector current will increase. The collector current of T2 is the base current of T1,there fore the collector current of T1 increases. But the collector current of T1 is the base current of T2. This action is accumulative since an increase of current in one transistor causes an increase of current in another transistor. As a result of this action both transistor driven to saturation, and heavy flows through the load RL. Under such condition SCR closes

47. SCR Characteristics

48. SCR Characteristics When anode is + ve with respect to cathode, the curve between V and I is called forward characteristics. In the above figure OABC is the forward characteristics of SCR at Ig = 0. When the supply voltage is increased from zero a point AB A reached, when SCR starts conducting. Under this condition, the voltage across the diode suddenly drops as shown in dotted line AB and most of the voltage appears across the load RL. When anode is negative with respect to cathode, the curve between V and I is known as reverse characteristics. If the reverse voltage is gradually increased, at first anode current remain small, and at some reverse voltage avalanche break down occurs and SCR starts conducting heavily in reverse direction as shown by the curve DE. The maximum reverse voltage at which starts conducting heavily is known as reverse breakdown voltage.

49. SCR as Half wave Rectifier

50. One important application of SCR is the controlled half wave rectification. The AC supply to be rectified is supplied through the transformer. The load RL is connected in series with Anode. The variable resistance r is inserted in the gate circuit to control the gate current During the - ve half cycle of the AC ,the SCR will not conduct. The SCR will conduct during the + ve half cycle provided ,proper gate current is made to flow. Greater the gate current ,the lesser the supply voltage at which SCR turned ON. Suppose that gate current is adjusted in such a way that SCR turns on at a voltage V 1 . The angle α is the firing angle at which SCR starts conduction. Hence conduction angle Ф = (180 – α) or (180 – ø )

51. An ordinary halfwave rectifier will conduct full + ve half cycles, where as SCR halfwave rectifier can be made to conduct at any point by adjusting the gate current. Therefore SCR can control the power fed to the load and hence name controlled rectifier. Let v = Vm Sin ø be the alternating voltage appearing across the secondary. Let α Be the firing angle. It means that rectifier will conduct from α to 180 during the + ve half cycle

52. Average voltage and Current

53. SCR as Full wave rectifier

54. The angle of conduction can be changed by adjusting the gate current Suppose the gate currents are so adjusted that SCR conducts as the secondary voltage becomes V1 Hence during the + ve half cycle of the AC input , the SCR1 will start conduction only when the voltage across the upper half of the secondary becomes V1 as shown in the graph. During the – ve half cycles of the AC input the SCR2 will conduct when the voltage across the lower half become V1. It may be seen that current through the load is in the same direction on both half cycles of the AC input.

55. Vav and Iav

56. Important Terms in SCR Breakover voltage Peak reverse voltage Holding current Forward current rating Circuit fusing rating Breakover voltage : It is the minimum forward voltage ,gate being open, at which SCR starts conducting heavily ie turned on. If the breakover vpltage of SCR is 200V, it means that it can block a forward voltage as long as supply voltage is less than 200V.If the supply voltage is more than this value,then SCR will be turned on . Peak Reverse voltage: It is the maximum reverse voltage (cathode + ve with respect to anode) that can be applied to an SCR without conducting in the reverse direction

57. Holding Current : It is the maximum anode current, gate being open, at which SCR is turned off from ON conditions. Thus if SCR has a holding current of 5mA ,it means that anode current is made less than 5mA ,then SCR will be turned off . Forward Current Rating: It is the maximum anode current that an SCR is capable of passing without destructions. If the value of the current exceeds this value ,SCR may be destroyed due to intensive heating at the junction Circuit fusing rating ( I 2 t ) : It is the product of the square of the forward surge current and the time duration of the surge. It indicate the maximum forward surge current capability of SCR.

58. TRIAC (TRIode for alternating current)

59. TRIAC A triac is a three terminal four layered semiconductor device whose forward and reverse characteristics are identical to forward characteristics of SCR. The three terminals are designed as main terminal MT1 ,main terminal MT2 and the Gate G. Figure( i ) above shows the basic structure of Triac. A Triac is equivalent to two separate SCR connected in reverse parallel( ie anode of each connected to cathode of the other) with gate connected as shown in figure (ii).Therefore the Triac acts like a bidirectional switch ie it can conduct current in either direction. figure(iii) shows the symbol of Triac.It consist of two parallel diode connected in opposite direction with a single gate terminal G. The gate provides the control over conduction in either direction.

60. TRIAC

61. TRIAC Triac is equivalent to two separate SCR connected in reverse parallel. Figure(a) shows the basic structure of SCR. If we split the basic structure in to two parts as shown in figure(b),we have two SCR as shown in figure(b),The left part in figure(b) consist of a pnpn device (p1n2p2n4) having three pn junction and constitutes SCR1. Simillarly the right part consist of another pnpn device(p2n3p1n1) having three pn junction and constitutes SCR2 .Suppose the main terminal MT2 is + ve and main terminal MT1 is - ve , if the Triac is fired in to conduction by proper gate current, the Triac will conduct as shown in figure(b) (left portion). In relation to figure ( c),SCR1 is ON and SCR2 is OFF. Now suppose MT2 is negative and MT1 is positive, with proper current Triac will be fired in to conduction. The current through the device will follow the path as shown in figure (b)(right portion).Now SCR2 ON and SCR1 OFF

62. TRIAC

63. TRIAC Mode of operations

64. TRIAC Mode of operation In mode 1 operation, MT2 is positive and Gate G is positive. In This mode the operation is identical to SCR. In mode 2 operation MT2 is negative and Gate G is positive. This is an ineffective mode and must be avoided. In mode 3 operation MT2 is positive and gate G is negative. This mode is less efficient than mode 1 but not as poor as mode 2. In mode 4 MT2 is negative and gate G is also negative. This mode is slightly less efficient than mode 1. The mode 1 and mode4 are efficient modes in TRIAC operation. These modes are called normal modes of TRIAC operation.

65. Difference between SCR & TRIAC SCR TRIAC It is unidirectional, ie it can conduct in forward direction only It is bidirectional, ie it can conduct in forward as well as in reverse direction It is triggered by a narrow positive pulse applied at the gate terminal It is triggered by a narrow pulse of either positive or negative polarity applied at the gate terminal SCR is available with large current rating Triacs are available with lower current rating, compared to that of SCR It has a fast turn off and therefore can be used to switch ac supply frequencies upto few kHz It has comparatively larger turn off time than SCR. Therefore, its use is limited to ac supply frequencies up to 400Hz

66. Merits, Limitations and applications of TRIAC Merits of TRIAC Triac is a bidirectional device, that is it can conduct in both direction Single gate controls the conduction in both direction Triacs with high voltage and current ratings are available Demerits of Triac Triacs are latching device like SCR, hence they are not suitable for DC power applications Gate has no control over the conduction once the Triac is turned on Triacs have very small switching frequencies Applications of Triac 1)AC power controllers and heaters, fan etc, controllers 2)Triggering device for SCRs

67. Power MOSFETs

68. Power MOSFETs A power MOSFETs have three terminals called Drain, Sources and Gate in place of corresponding three terminals collector, emitter and base for BJT. The circuit symbol of power MOSFETs is shown above. The arrow indicates the direction of electron flow. A BJT is a current controlled device, where as power MOSFETs is a voltage-controlled device. As its operation depend on the flow of majority carriers only, MOSFETs is a unipolar device. The control signal or base current in BJT is much larger than control signal (gate current) required in MOSFETs. This is because the gate circuit impedance in MOSFETs is extremely high, of the order of 10 9 ohm. This large impedance permits the MOSFETs gate to be driven directly from microelectronic circuits suffers from second breakdown voltage, where as MOSFETS is free from this problem. power MOSFETs are finding increasing applications in low power high frequency converters. Power MOSFETS are of two types, n channel enhancement MOSFETs and p channel enhancement MOSFETs

69. Power MOSFETs N channel enhancement MOSFETs is more common because of higher mobility of electrons. The simplified structure of n channel planar MOSFETs of low power rating is shown above. On p substrate (or body), two heavily doped n+ region are diffused as shown. An insulating layer of silicon dioxide(sio2) is grown on the surface. Now insulating layer is etched in order to embed metallic source and drain terminals. note that n+ region makes contact with sources and drain terminals as shown in figure. A layer of metal is also deposited on SIO2 layer so as to form the gate of the MOSFETs When the gate circuit is open, no current flow from drain to sources and load because of one reversed biased n+p junction. When the gate is made positive with respect to sources, an electric field is established as shown in figure. Eventually induced negative charges in the p substrate below sio2 layers are formed. These negative charges called electron, from n channel and current can flow from drain to sources as shown by arrows

70. Power MOSFETs If Vgs is made more positive, n channel become more deep and there fore more current flows from D to S. This shows that the drain current Id is enhanced by the gradual increase of gate voltage and the name enhancement MOSFETs. The main disadvantage of n channel planar MOSFETs is that conducting n channel in between drain and sources gives large on state resistances. This leads to high power dissipation in n channel. This shows that planar MOSFETs constructions is feasible only for low power MOSFETS

71. High Power MOSFETs

72. High power MOSFETs The construction details of high power MOSFETs are shown above. In this figure shown a planar diffused metal oxide semiconductor (DMOS) structure for n channel which is quite common for power MOSFETs. on n+ substrate, high resistivity n- layer is epitaxially grown. The thickness of n- layer determine the voltage blocking capability of the device. On the other side of n+ substrate, a metal layer is deposited to form the drain terminal. Now p- layer is diffused in the epitaxially grown n- layer. further n+ region are diffused in p- region as shown. As before SIO 2 layer is added, which is then etched so as to fit metallic source and gate terminals. A power MOSFETS actually consist of parallel connection of thousands of basic MOSFETs cell on the same single chip silicon Power MOSFETS conduction is due to majority carriers, therefore the time delay caused by removal or recombination’s of majority carriers are eliminated. Thus, power MOSFETS can work at switching frequencies in the megahertz range

73. Merits & Demerits of MOSFETs Merits of MOSFETs MOSFETs are majority carrier device MOSFETs have positive temperature coefficients MOSFETs have very simple driver circuits MOSFETS have short turn off and turn on times ,hence they operate at high frequencies MOSFETs do not require commutation circuits Gate has full control over the operation of MOSFETs Demerits of MOSFETs On state loss in MOSFETs are very high MOSFETs are used only for low power applications MOSFETs suffer from static charges

74. Applications High frequency low power inverters High frequency SMPS High frequency inverters and choppers Low power AC and DC drivers

75. Difference between BJT & MOSFETs Sl no BJT MOSFETs 1 This is a bipolar device This is mobility carrier device 2 Controlled by base Controlled by Gate 3 Current controlled devices Voltage controlled device 4 Negative temperature coefficients Positive temperature coefficients 5 Losses are low Losses are higher than BJT 6 Drive circuit is complex Drive circuit is simple 7 Switching frequency is lower Switching frequency is high 8 BJT suitable for high power application MOSFETs suitable for low power applications

76. IGBT ( Insulated Gate Bipolar Transistor) IGBT is the latest device in power electronics . It is obtained by combining the property of BJT and MOSFET . We know that BJT has lower on state loss for higher values of collector current. But the drive requirement of BJT is little complicated. The drive of MOSFET is very simple. But the MOSFET has high on state loss. The gate circuit of MOSFET and collector emitter circuit of BJT are combined together to form a new device .This device is called IGBT . Thus IGBT has the advantage of both BJT and MOSFET . The symbol of IGBT is given below. Symbol indicate the combination of MOSFET and BJT.

77. IGBT The IGBT has three terminal, Gate (G), collector ( C ) , and emitter ( E ) .Current flow from collector to emitter whenever a voltage between gate and emitter is applied. The IGBT is said to have turned ‘ ON’ . When the gate emitter voltage is removed, IGBT is turned off. Thus gate has full control over conduction of IGBT. When the gate to emitter voltage is applied, a very small current flows. This is similar to gate circuit of MOSFET . The on state collector to emitter drop is very small like BJT .

78. Basic Structure & Working of IGBT The basic structure is shown above . The p+ injecting layer is heavily doped. It has the doping density of 10 19 per cm3.The doping of other layer is similar to that of MOSFETs. The n+ layer also have the doping density of 10 19 per cm3. P type body region has the doping level of 10 16 per cm3.The n- drift region is lightly doped ie 10 14 per cm3.

79. IGBT The basic structure of IGBT is almost same as powerMOSFET However ,there is a difference in substrate The n+ substrate at the Drain in power MOSFET is substituted In the IGBT by p+ substrate called collector When V GS, greater than V GS (threshold), the channel of electron is formed below the gate as shown in the diagram . These electron attracts holes from p+ layer. Hence holes are injected from p+ layer in to n- drift region. Thus holes/electron current starts flowing from collector to emitter . when the holes enter p type body region, they attract more electrons from n+ layer. This action is exactly similar to MOSFET

80. IGBT Merits It is a voltage controlled device .Hence driver circuit is very simple On state losses are reduced Switching frequencies are higher than thyristors No commutation circuits are required Gate have full control over the operation of IGBT IGBT have approximately flat temperature coefficient Demerits IGBT have static charge problems IGBT are costlier than BJT and MOSFET Application of IGBT AC motors drivers, ie inverters DC to DC power supplies, ie choppers UPS systems Harmonic compensators.

81. IGBT – Characteristics The static VI or output characteristics of an IGBT is shown above, It is the graph between V CE versus I C for different value of V GE. In the forward direction, the graph is similar to that of BJT.But here the controlling parameter is the V GE because IGBT is a voltage controlled device The transfer characteristics is the graph between I C versus V GE as shown in figure c.This is similar to that of power MOSFET .When VGE is less than the threshold voltage ,IGBT is in the off state.

82. UNINTERRUPTED POWER SUPPLY (UPS) An uninterruptible power supply , also uninterruptible power source , UPS or battery/flywheel backup , is an electrical apparatus that provides emergency power to a load when the input power source, typically mains power , fails

83. UPS A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide near-instantaneous protection from input power interruptions, by supplying energy stored in batteries, supercapacitors, or flywheels . The on-battery runtime of most uninterruptible power sources is relatively short (only a few minutes) but sufficient to start a standby power source or properly shut down the protected equipment . A UPS is typically used to protect hardware such as computers, data centers, telecommunication equipment or other electrical equipment where an unexpected power disruption could cause injuries, fatalities, serious business disruption or data loss. UPS units range in size from units designed to protect a single computer without a video monitor (around 200 volt-ampere rating) to large units powering entire data centers or buildings.

84. UPS The primary role of any UPS is to provide short-term power when the input power source fails. However, most UPS units are also capable in varying degrees of correcting common utility power problems : Voltage spik e or sustained overvoltage Momentary or sustained reduction in input voltage Noise, defined as a high frequency transient or oscillation, usually injected into the line by nearby equipment Instability of the mains frequency Harmonic distortion: defined as a departure from the ideal sinusoidal waveform expected on the line

85. Classification of UPS Offline/Standby UPS Line -interactive Online/double-conversion

86. UPS- Standby

87. UPS Power is normally directly taken from the Utility with some filtering and surge protection. When the utility fails, the power switches to the inverter. The term standby is due to the battery and DC/AC inverter being in standby most of the time. There is a slight break in output power of several tens of milliseconds that wouldn't affect most computers and devices but may very adversely affect Industrial Control systems. These are electrically more efficient in normal operation and low cost.

88. UPS- Line interactive

89. Power is also normally directly taken from the utility with more active filtering for a better waveform output. When the utility has some distortions outside of set boundaries, the Inverter kicks in the direction from DC to AC . As the inverter is constantly connected to the output, there is no break in output power during switching from utility to battery. So these are also used by Industrial Control systems. These are less efficient and higher cost.

90. UPS – Double conversion

91. Power is always converted from the utility's AC to DC and back to AC to the output. When the utility blacks out, the battery starts to supply to the DC portion instead of the rectifier. As the output power is constantly generated by the inverter, it's output waveform is the most perfect of all . So these are suitable for use by any application that demands high quality electrical supply. Due to the constant double conversion, they are less efficient and higher cost due to the additional components.

92. INVERTER A n inverter is used to produce an un-interrupted 220V AC or 110V AC (depending on the line voltage of the particular country) supply to the device connected as the load at the output socket. The inverter gives constant AC voltage at its output socket when the AC mains power supply is not available.

93. Block diagram of inverter

94. When the AC mains power supply is not available. An oscillator circuit inside the inverter produces a 50Hz MOS drive signal. This MOS drive signal will be amplified by the driver section and sent to the output section. MOSFETs or Transistors are used for the switching operation. When these switching devices receive the MOS drive signal from the driver circuit, they start switching between ON & OFF states at a rate of 50 Hz . This switching action of the MOSFETs or Transistors cause a 50Hz current to the primary of the inverter transformer. This results in a 220V AC or 110V AC (depending on the winding ratio of the inverter transformer) at the secondary or the inverter transformer. This secondary voltage is made available at the output socket of the inverter by a changeover relay.

95. When the AC mains power supply is available. The AC mains sensor senses it and the supply goes to the Relay and battery charging section of the inverter . AC main sensor activates a relay and this relay will directly pass the AC mains supply to the output socket. The load will by driven by the line voltage in this situation. Also the line voltage is given to the battery charging section where the line voltage is converted to a DC voltage(12V DC or 24V DC usually),then regulated and battery is charged using it . There are special circuits for sensing the battery voltage and when the battery is fully charged the charging is stopped. In some inverters there will be a trickle charging circuit which keeps the battery constantly at full charge.

96. Automation in an Inverter. I nverter contains various circuits to automatically sense and tackle various situations that may occur when the inverter is running or in standby. This automaton section looks after conditions such as overload, over heat, low battery, over charge etc. Respective of the situation, the automation section may switch the battery to charging mode or switch OFF. The various conditions will be indicated to the operator by means of glowing LEDs or sounding alarms. In advanced inverters LCD screens are used to visually indicate the conditions.

97. What is Difference between UPS & Inverter We are heavily dependent upon appliances that run on electricity such as fans, lights, AC, fridge, Computer and so on. Whenever there is a power cut, electricity supply to these appliances is cut off and they stop working. However, if we have backup supply devices such as UPS and inverter, we can ensure Power supply to appliances and not bothered with power cuts. However, people remain confused with the difference between a UPS and an inverter because UPS and inverters both are providing back up power supplies during main power outage. Inverters are preferred more for general electric appliances whose working does not get affected by extended delays in power supply. UPS are used for electronics appliances such as computer, servers, workstations, Medical Equipment which perform critical task and cannot tolerate delays in power supply. An off-line ups (the standard) switch to the batteries in 3 to 8 milliseconds, after the main power has been lost. While Inverter changes over in about 500 milliseconds.

98. UPS UPS means uninterrupted power supply. Uninterruptible power supply (UPS) provides uninterrupted power to the equipment. It means switching time from power cut to battery power is vey less hence important and critical equipment like computer, desktop .Medical Instruments is not switch off and we can lose data. A UPS is a complete system that is consisting of many parts that include batteries, a charge controller, circuitry any transfer switch for switching between the mains and back-up battery, and an inverter. An inverter is needed because the battery can only store DC power and we need to convert that back to AC in order to match the appliances connected in the main power line. UPS= Battery charger + Inverter UPS is nothing but inverter with inbuilt battery charger. UPS give backup only 10 to 20 minutes. The main intention of it is to provide backup only for small time so that you can save the programs and data. UPS also gives protection against line abnormalities like Surge, Voltage fluctuation, Under Voltage, Over Voltage, Spike, Noise.

99. Inverter Inverter circuit simple converters battery DC current to AC and supply In inverter inverts the direct current to an alternating current. During normal condition electrical supply is direct feed to the Load. It also takes the supply from the AC source and charges the battery. During the power cut, the inverter receives the supply from the battery and convert it DC to AC Power and provides the power supply to the electrical equipment. Inverters purpose is to provide power backup to total home appliances, lights, fans. Inverter uses flat plate or tubular battery to store electricity. So it requires continuous maintenance, needs to fill the distilled water toppings at regular intervals of time. Inverter does not give protection against line abnormalities

100. Conclusion The UPS and inverter both provide the backup supply to the electrical system. Two major differences between the UPS and inverter are that The switching of UPS from the main supply to the battery is very immediate so it is used to provide backup power of important or critical electronics equipment. whereas in inverter the switching from mains supply to battery takes times so it used to provide less important electrical equipment . The UPS provide protection to the load against Spike, Voltage fluctuation, Noise while Inverter does not provide any protection to the load.

101. Comparison between UPS & INVERTER Descriptions UPS Inverter Definition UPS means Uninterruptable Power Supply. Inverter is a device which converts DC electricity to AC Function It is an electric circuit (device) which instantly backs up power supply for a gadget. The gadgets works continues to work on smoothly and there is no damage to it.   Inverter consist circuitry which converts AC to DC and stores in the battery. When power supply goes off, that DC power is converted back to AC and is transmitted to the respective electronic gadget. Principles It first converts AC to DC Power to charge the battery than Convert DC Power to AC Power (Inverter) and this AC power is supplied to Load. However, UPS monitors the input voltage level and processes it in terms of voltage regulations. UPS= Battery charger + Inverter Inverter converts DC power (stored in its battery) to AC Power supplied to the devices. Normally AC Power charges the battery .It uses relays and sensors to detect when to use DC power or AC Power, for DC power.

102. Back up Time Power Back up for Short Duration Power Back up for Long Duration Types (a) Offline UPS, (b) Online UPS and (c) Line-interactive UPS.   (a) Square Wave, (b) Quasi Wave, (c) Sine Wave Main Part Rectifier/charger, Inverter ,controller Inverter and controller. Switch over Time 3 to 8 milliseconds. 500 milliseconds. Voltage Fluctuations While voltage fluctuations in input supply can be adjusted by the UPS, the output voltages are desired to be as smooth as possible. In smoothing the voltage outputs, UPS are considered better as compared to inverter.   Inverter does not give protection against voltage fluctuations

103. Circuitry Sophistication UPS circuitry is far more sophisticated than that of inverter’s Inverter has Simple circuit then UPS Pricing UPS more expensive than an inverter. Inverter is less expensive than UPS Application UPS are used for electronics Application such as computer, servers, Network Switches, workstations, Medical Equipment, Processing Equipment which perform critical task and cannot tolerate delays in power supply. Inverters are preferred more for general electric Application which working does not affected by extended delays in power supply. Protection UPS provide protection against voltage spikes, voltage drops, instability of the main frequency and harmonic distortions Inverter does not provide protection against Line abnormalities. Battery Used sealed maintenance free (SMF) battery Used flat plate or tubular battery Battery Maintenance Do not require any maintenance. Requires continuous maintenance, needs to fill the distilled water toppings at regular intervals of time Energy Consumption More due to constant battery Charging Less

104. SMPS

105. SMPS A switched-mode power supply ( switching-mode power supply , switch-mode power supply , switched power supply , SMPS , or switcher ) is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently . Like other power supplies, an SMPS transfers power from a source, like mains power, to a load, such as a personal computer, while converting voltage and current characteristics. Unlike a linear power supply, the pass transistor of a switching-mode supply continually switches between low-dissipation, full-on and full-off states, and spends very little time in the high dissipation transitions, which minimizes wasted energy. Ideally, a switched-mode power supply dissipates no power. Voltage regulation is achieved by varying the ratio of on-to-off time .

106. In contrast, a linear power supply regulates the output voltage by continually dissipating power in the pass transistor. This higher power conversion efficiency is an important advantage of a switched-mode power supply. Switched-mode power supplies may also be substantially smaller and lighter than a linear supply due to the smaller transformer size and weight . A linear regulator provides the desired output voltage by dissipating excess power in o hmic losses (e.g., in a resistor or in the collector–emitter region of a pass transistor in its active mode). A linear regulator regulates either output voltage or current by dissipating the excess electric power in the form of heat , and hence its maximum power efficiency is voltage-out/voltage-in since the volt difference is wasted.

107. In a SMPS, the output current flow depends on the input power signal, the storage elements and circuit topologies used, and also on the pattern used (e.g., pulse-width modulation with an adjustable duty cycle) to drive the switching elements. The spectral density of these switching waveforms has energy concentrated at relatively high frequencies. As such, switching transients and ripple introduced onto the output waveforms can be filtered with a small LC filter

108. Advantages & Disadvantages The main advantage of the switching power supply is greater efficiency because the switching transistor dissipates little power when acting as a switch. Other advantages include smaller size and lighter weight from the elimination of heavy line-frequency transformers, and lower heat generation due to higher efficiency. Disadvantages include greater complexity, the generation of high-amplitude, high-frequency energy that the low-pass filter must block to avoid electromagnetic interference (EMI), a ripple voltage at the switching frequency and the harmonic frequencies thereof . Very low cost SMPSs may couple electrical switching noise back onto the mains power line, causing interference with A/V equipment connected to the same phase. Non-power-factor-corrected SMPSs also cause harmonic distortion.

109. Block diagram of SMPS

110. Input rectifier stage If the SMPS has an AC input, then the first stage is to convert the input to DC. This is called rectification . A SMPS with a DC input does not require this stage. In some power supplies (mostly computer ATX power supplies ), the rectifier circuit can be configured as a voltage doubler by the addition of a switch operated either manually or automatically. This feature permits operation from power sources that are normally at 115 V or at 230 V. The rectifier produces an unregulated DC voltage which is then sent to a large filter capacitor

111. Inverter stage This section refers to the block marked chopper in the diagram. The inverter stage converts DC, whether directly from the input or from the rectifier stage described above, to AC by running it through a power oscillator, whose output transformer is very small with few windings at a frequency of tens or hundreds of kilohertz. The frequency is usually chosen to be above 20 kHz, to make it inaudible to humans. The switching is implemented as a multistage (to achieve high gain) MOSFET amplifier. MOSFETs are a type of transistor with a low on-resistance and a high current-handling capacity.

112. SMPS Voltage converter and output rectifier If the output is required to be isolated from the input, as is usually the case in mains power supplies, the inverted AC is used to drive the primary winding of a high-frequency transformer. This converts the voltage up or down to the required output level on its secondary winding. The output transformer in the block diagram serves this purpose . Regulations A feedback circuit monitors the output voltage and compares it with a reference voltage, as shown in the block diagram above. Depending on design and safety requirements, the controller may contain an isolation mechanism (such as an opto-coupler) to isolate it from the DC output. Switching supplies in computers, TVs, VCRs and for smartphones/tablets have these opto-couplers to tightly control the output voltage.