POWER TRANSISTORS AND THEIR TYPES

✏️POWER TRANSISTORS AND THEIR TYPES

📌Power transistors have controlled turn-on andturn-off characteristics.The power transistors can be classified broadly into five categories:

1. Metal oxide semiconductor field-effect transistors(MOSFETs)

2. COOLMOS

3. Bipolar junction transistors (BJTs)

4. Insulated-gate bipolar transistors (IGBTs)

📌Power MOSFETs

👉A power MOSFET is a voltage-controlled device and requires only a smallinput current.

👉The switching speed is very high and the switching times are of the order ofnanoseconds.Power MOSFETs find increasing applications in low-power high-frequencyconverters.

👉MOSFETs have the problems of electrostatic discharge and require specialcare in handling.

 👉it is relatively difficult to protect them under short-circuited fault conditions. 

The two types of MOSFETs are (1)depletion MOSFETs and 

(2) enhancement MOSFETs. 

👉An n-channel depletion-type MOSFET is formed on a p-type silicon substrate, with two heavily doped n+ silicon sections for low resistance connections.

 👉The gate is isolated from the channel by a thin oxide layer. 

👉The three terminals are called gate, drain, and source. The substrate is normally connected to the source. 

👉The gate-to-source voltage VGS could be either positive or negative. 

👉If VGS is negative, some of the electrons in the n-channel area are repelled and adepletion region is created below the oxide layer, resulting in a narrower effective channel and a high resistance from the drain to source RDS. 👉If VGS is made negative enough, the channel becomes completely depleted,offering a high value of RDS, and no current flows from the drain to source, IDS= 0. The value of VGS when this happens is called pinch-off voltage VP.

👉 On the other hand, if VGS is made positive, the channel becomes wider,and IDS increases due to reduction in RDS. 

👉With a p-channel depletion-type MOSFET,the polarities of VDS, IDS, and VGS are reversed. 

👉An n-channel enhancement-type MOSFET has no physical channelIf VGS is positive, an induced voltage attracts the electrons from the p-substrate and accumulates them at the surface beneath the oxide layer.

👉If VGS is greater than or equal to a value known as threshold voltage VT, a sufficient number of electrons are accumulated toform a virtual n-channel, as shown by shaded lines in Figure,and the current flows from the drain to source.

👉The polarities of VDS, IDS,and VGS are reversed for a p-channel enhancement-type MOSFETs. 

👉Because a depletion MOSFET remains on at zero gate voltage,where as an enhancement-type MOSFET remains off at zero gate voltage, the enhancement-type MOSFETS are generally used as switching devices in power electronics.

👉In order to reduce the on-state resistance by having a largercurrent conducting area, the V-type structure is commonly used for power MOSFETs.

👉The cross section of a power MOSFET known as a vertical (V) mosfet. 

👉When the gate has a sufficiently positive voltage with respect to thesource, the effect of its electric field pulls electrons from the n+ layer intothe p layer. 👉This opens a channel closest to the gate, which in turn allows the current to flow from the drain to the source.

👉There is a silicon oxide (SiO2) dielectric layer between the gate metal and then+ and p juncon.

 👉MOSFET is heavily doped on the drain side to create an n+ buffer below the n‐ drift layer. 

👉This buffer prevents the depleon layer from reaching the metal, and also reduces the forward voltage drop during conduction.

👉MOSFETs require low gate energy, and have a very fast switching speed and low switching losses. 

👉The input resistance is very high, 109 to 1011 Ω.MOSFETs, however, suffer from the disadvantage of high forward on-state resistance as shown in Figure above , and hence high on-state losses, which makes them less attractive as power devices, but they are excellent as gate amplifying devices for thyristors etc. 

👆CROSS SECTION OF N-CHANNEL MOSFET👆

👆CROSS SECTION OF P-CHANNEL MOSFET👆

WORKING OF STIRLING OR BRAYTON HEAT ENGINE

✏️WORKING OF A STIRLING ENGINE OR A BRAYTON HEAT ENGINE 

📌The  array  of  mirrors  focuses  the    sunlight the  concentrated  sunlight  then    heats  up the  working  fluid  to  temp  of    around 750˚C  with  in  the  receiver. 

📌The  heated  high  temp  working  fluid  is then  used  in  either  a  Stirling  or  Brayton heat  engine  cycle  to  produce  mechanical power  via  rational  kinetic  energy  and  then electricity  for  utility  use  with  an  electric generator.

📌When  the starter  of  the  engine  is  switched  on  by the  operator,  the  external  heat  energy  source starts.  (Intensity  of  which  can  be  controlled  by the  operator  through  a  provided  mechanism). 

📌After  starting  the  heat  source  the  heat  is transferred  from  heat  source  to  the  hot  cylinder walls,  which  in  turn  raises  the  temperature  of the  gas  inside  the  hot  cylinder  due  to  which disturbance  in  the  molecules  of  the  gas  occurs because  of  the  kinetic  energy  provided  by increased  temperature. 

📌This  disturbance  increases  the  molecular pressure  over  the  surface  of  the  piston  inside the  hot  cylinder  in  order  to  expand  the  gas, which  in  turn  pushes  the  piston  away  for  the expansion.

📌When  the piston  moves  away  i.e.  from  TDC  to BDC  due to the  expansion  provided  by  the  hot gas  the  crank  shaft  rotates  which  is considered  to  be  the  work  output. 

📌When  this  hot  cylinder  piston  moves  from  BDC to  TDC  due  to which  the  cold  cylinder  piston moves  from  TDC  to BDC,  the  hot  piston  starts pushing  the  hot  gas  into  the  cold  cylinder  for cooling. 

📌The  cooling  system  associated  with  the  cold cylinder  instantly  cools  the  entering  hot  gases from  the  hot  cylinder. From  TDC  to BDC.  

📌Which  in  turn  compressing the  cold  gas  inside  the  cold  cylinder  due  to which  the  cold  gas  moves  from  cold  cylinder  to the  hot  cylinder  for  the  further  cycles.

Assembly programming and Instruction of 8051

✏️Assembly programming and Instruction of 8051

👉Subroutine

👉Call instruction

👉Nested loop

✏️SUBROUTINE 

📌In assembly language programming it is common to have one main program and many sub routines that are called from the main program.

📌The is allows to make separate module of program known as subroutine. 

📌Each module can be tested separately and brought together in main program.

📌More importantly, in a large program the modules can be assigned to different programmers to shorten development time.

✏️CALL INSTRUCTIONS

👉LCALL (long call)

👉ACALL (absolute call)

📌LCALL (LONG CALL)

 👉It is a 3 byte instruction. 

👉The first byte is the opcode and second and third are used address of  target subroutine.

👉This can be used to call subroutines located anywhere within the 64K-byte address space of 8051.

👉When a subroutine is called, control is transferred to that subroutine, processor saves the program counter and begins to fetch instructions from new location.

👉 After execution the subroutine, thee instruction RET (return) control back to the caller. 

Syntax : LCALL LABEL

✏️ACALL (ABSOLUTE CALL) 

👉ACALL is a 2-byte instruction. 

👉Only 11 bits are used as address. 

👉While the target address of ACALL must be within a 2K-byte range. In variation of the 8051,  on-chip ROM is as low as 1K byte.

👉 In such cases, the use of ACALL instead of LCALL can save a number of bytes of ROM space.

Syntax : ACALL LABEL

✏️NESTED LOOPS

👉A loop within a loop, an inner loop within the outer one 

👉The first pass of outer loop triggers the inner loop which executes to completion. 

👉Then the second pass of outer loop of outer loop triggers inner loop again

👉This repeats till outer loop FINISHES. 

📌SYNTAX

for (initialize counter; test condition; ++ or –)

{

for (initialize counter; test condition; ++ or --)

{

.// inner loop

}

.//outer loop

}

Memory Architecture of 8051 microcontroller

✏️Memory  Architecture of 8051 microcontroller

📌Von  Neumann  Architecture 

📌Harvard  Architecture 

📌This classification organization of a is mainly program based on memory(ROM) data memory(RAM). 

✏️Von  Neumann  Architecture 

👉 It  is also referred  as Princeton  Architecture.

 👉It has a single memory storage tohold both program  Instructions and data instructions .... For example :common program and storage space. 

👉Instructions and data are accessed during same bus system. 

 ✏️Advantage : 

👉Simple design of microcontroller chip. 

👉Reduces  required hardware . 

✏️Disadvantage : 

👉Slower excution  of a program. 

✏️Harvard  Architecture

👉It has physically separate memory storage to hold program Instructions and data i.e separate program and data space.

👉Since it has separate buses to access program and data memory it is possible to access program memory and data memory simultaneously.

✏️Advantage:

👉Faster operation.

✏️Disadvantage:

👉It requires more hardware. 

NOTE:

👉8051 family architecture are based on Harvard Architecture.

C DATA TYPES FOR 8051 MICRO-CONTROLLER

✏️C DATA TYPES FOR 8051 MICRO-CONTROLLER

📌Unsigned char:

1.The most widely used data types for the 8051. 

2.The unsigned char is an 8-bit data type. 

3.The range of  unsigned char is 0-255(0-FF).

Used for:

counter value.

ASCII  Character.

📌Signed char:

1.Signed char is an 8 bit data type.

2.Use the MSB D7 to represent - or +.

3.The range of signed char - 128 to +128.

📌Unsigned int:

1.The unsigned int is an 16-bit data type.

2.Takes the value in the range 0-65535(0-FFFFH).

Used for:

Define 16bit variable such as memory addresses.

Set the counter values of more than 256.

📌Signed int:

1.Signed int is an 16bit data type.

2.use the MSB D15 to represent - or +.

3.We have 15bits for the magnitude of the number - 32768 to +32767.

📌Bit, Sbit, Sfr:

1.The bit data type allows access to single bits of bit - addressable memory spaces 20-2FH.

2.To access bits of SFRs, we use sbit data type.

3.To access the byte-size SFR registers, we use SFR data type. 

ASSEMBLER DIRECTIVES

✏️ASSEMBLER DIRECTIVES

Assembler directives are instructions that direct the assembler to do something. This is used to set the program or register address during assembly.

✏️Types of assembler directives are:

📌ORG (origin):-

 The origin (ORG) directive is used to indicate the beginning of the addresses the number that comes after ORG can be either in hex or in decimal if the number is not followed by H it is decimal and the assembler will convert it to hex.

         Ex:- ORG 0000H

📌EQU (equate):-

    This is used to define a constant without occupying a memory location. The EQU directive does not set aside storage for a data item but associates a constant value with a data label so that when the label appears in the program its constant value will be substituted for the label to use EQU for the counter constant and then the constant is used to load the register.

   Ex:-

       COUNT EQU 25

       MOV R3, # COUNT

📌END:-

The END directive indicates to the assembler at the end of the source (asm) file.The END directive is the last line of an 8051 program meaning that in the source code anything after the END directive is ignored by the assembler.

📌DB (define byte) :-

The define assembler directive is used for allocation of storage space. It can be used to reserve as well as initialize one or more bytes.

📌DW (define word) :-

Define Word [DW]- The DW directive defines items that are one word (two bytes) in length.

Define Double word [DD]- It defines the data items that are a double word (four bytes) in length.

Define Quad word [DQ]- This directive is used to tell the assembler to declare variable 4 words in length or to reserve 4 words of storage in memory.

Vapour-Compression refrigeration cycle

✏️Vapour-Compression  refrigeration  cycle

📌 The  vapour-compression  refrigeraon  cycle  is  the most  common cycle based  on which  most HVAC devices  works.

📌 It  consists  of  four  basic  components,  namely, compressor,  condenser,  evaporator,  and  expansion valve.  In  an  ideal  vapour-compression  refrigeraon cycle,  the  refrigerant  enters  the  compressor  as  a saturated  vapour  and  is  compressed  isentropically.

 📌Compressed  vapour  is  cooled  in  a  condenser  to  the saturated  liquid  state  and  then  expands  from  high pressure  to  low  pressure  in  the  expansion  device. 

📌A mixture  of  the  refrigerant  liquid  and  vapour  comes  out  of the  expansion  valve,  where  the  majority  is  liquid,  and evaporaon  of  the  liquid  in  the  evaporator  give  out  latent heat  of  evaporaon,  which  is  known  as  cooling  effect.

✏️Performance  of  Vapour-Compression  Refrigeraon  cycle

The  performance  of the  measure  in  terms of COP as given  in  eqn. COPR=QR/Win=h1-h4/h2-h1 Here,  QR  is refrigeraon  effect  (amount  of heat  removed  in  evaporator) and  Win  is work  input  to  the  compressor. 

✏️Parts  of  a  Vapour-Compression  cycle 

Condenser :Compressed  high  pressure  and  high  temperature  refrigerant vapour  comes  to  the  condenser,  where  it  is  condensed  to  liquid state  by  removing  its  latent  heat  and  subcooled  by  removing sensible  heat. 

📌Air  or  water  is  used  to  remove  heat  of  the  refrigerant.  Both have  their  inherent  advantages  and  allocaon. 

📌 Air  cooled  condenser  does  not  require  water,  simple  and  less maintenance  is  involved  but  works  at  higher  condensaon temperature  and  air  having  less  heat  carrying  capacity  requires more  heat  transfer  surface  area.

Expansion  Valve:

📌The  funcon of  an expansion  valve  is  to  meter  the  liquid  refrigerant in  the  evaporator  and maintain  a  pressure  difference  between  the  condenser  and evaporator.  Different  expansion  Valves,  float  valve,  thermostac, electronic  or  balance  expansion  valve,  capillary  tube  etc. 

📌A capillary  tube  is  the  simplest  expansion  device  to  produce  pressure difference.  It  is  made  of  a  small  diameter  tube  and  is  suitable  for company  assembled  devices  like  refrigerator,  water,  cooler,  display type  cabinets,  window  air  condioners,  etc. 

📌It  cannot  regulate  the  amount  of  refrigerant  so  it  is  suitable  for  fixed f low machines.

Evaporator:

📌Refrigerant  evaporates  and  absorbs  latent  heat  of  evaporaon  from  the surroundings  in  an  evaporator.  An  air  cooled  heat  exchangers  are  shell and  tube  type  or  plate  type.  Shell  and  tube  evaporators  are  divided  into dry  type  or  flooded  type  evaporators. 

Refrigerant : 

📌The  refrigerant  plays  the  role  of  absorbing  and  transming  heat  in  a vapour  compression  refrigeraon  system.  Most  common  desirable properes  of  a refrigerant  are  pressure  temperature  relaonship, freezing  point,  chemical  stability,  toxicity,  ozone  depleon  potenal, Global  warming  potenal,  and  cost.  CFCs  were  popular  refrigerants  in the  last  century  and  they  have  now  been  replaced  with  HFCs  and  HCFCs to  save  the  environment.

✏️Energy  Use  Indices

📌 According  to  ASRAE  standards,  following  are  the  current  energy  use indices  for  refrigeraon  compressors,  packaged  units,  heat  pumps,  and chillers: 

1.  Coefficient  of  Performance  (COP)  is  the  rao  of  cooling  capacity  in  kW  to the  total  power  input  in  kW,  at  any  given  set  of  rang  condions. COP=Refrigeraon  effect  kW/Work  input  kW

 2.  Energy  efficiency  rao  is  defined  as  the rao  of  net  cooling  capacity  of  a refrigeraon compressor,  a  packaged  unit,  or  other  device,  in  BTU/h,  to  the  electric power  input  to  that  device,  in  W,  under  designated  operang  condions. EER=Refrigeraon  effect  BTU/hr/Work  input  w

3.  kW/ton  indicates  the  electric  power  consumpon  of  a refrigerang compressor  per  ton  of  refrigeraon  effect. kW/ton=Work  input kW/Refrigeraon  effect ton. 

✏️Impact  of  Refrigerants  on  Environment  and  Environment  and  Global Warming 

📌The  surface  of  the  earth  is  surrounded  by  a layer  of  air,  called  the atmosphere.  The  lower  atmosphere  is  called  the  hemisphere,  and  the upper  atmosphere  is  called  stratosphere. 

📌They  are  very  stable.  Halons  are  also  halogenated  hydrocarbons. If  CFCs  and  halons  leak  or  are  discharged  from  a  refrigeraon  system during  operaon  or  repair  to  the  lower  atmosphere,  they  will  migrate to  the  upper  stratosphere  and  decompose  under  the  acon  of ultraviolet  rays  throughout  decades  or  centuries.

📌A cloudless  hemisphere  is  mainly  transparent  to  short  wave  solar radiaon  but is  quite  opaque  to  long  wave  infrared  rays  emied  from the  surface  of  the  earth.

📌Carbon  dioxide  has  the  greatest  blocking  effect  of  all;  water  vapour and  synthec  CFCs also  play  important  roles  in  blocking  the  direct escape  of  infrared  rays  is  called  the  greenhouse  effect. 

📌 The  increase  of  the  CO2,  vapour,  CFCs,  and  other  gases,  oen  called greenhouse  gases,  eventually  will  result  in  a  rise  in  air  temperature near  the  earth’s  surface.  This  is  known  as  the  global  warming  effect.