Microprocessor and Microcontroller

 INTRODUCTION TO MICROPROCESSOR AND MICROCOMPUTER ARCHITECTURE

    A microprocessor is a programmable            electronics chip that has computing and       decision   making capabilities similar to      centra   processing unit of a    computer     Any microprocessor   based systems             having limited number of    resources           are   called microcomputers.   Nowadays,     microprocessor can be seen in almost           all types of electronics devices like                   mobile phones,    printers, washing              machines etc.   Microprocessors are also     used in    advanced applications like             radars, satellites and flights. Due to the        rapid advancements in electronic                   industry and large scale integration of           devices results in a significant cost                 reduction and increase application of            microprocessors and their derivatives.

 Bit: A bit is a single binary digit.

 Word: A word refers to the basic data         size or bit size that can be processed by        the arithmetic and logic unit of the                processor. A 16-bit binary number is              called a word in a 16-bit processor.

 Bus: A bus is a group of wires/lines that          carry similar information.

 System Bus: The system bus is a group of wires/lines used for communication 

between the microprocessor and peripherals.

 Memory Word: The number of bits that can be stored in a register or memory element is called a memory word.

 Address Bus: It carries the address,              which is a unique binary pattern used           to   identify a memory location or an             I/O     port. For example, an eight bit              address bus      has eight lines and thus         it can address 28= 256 different                    locations. The locations in hexadecimal         format can be written as 00H – FFH.

 Data Bus: The data bus is used to                    transfer data between memory and                 processor or between I/O device and              processor. For example, an 8-bit                   processor will generally have an 8-bit           data bus and a 16-bit processor will                have 16-bit data bus.

 Control Bus: The control bus carry                control signals, which consists of signals       for selection of memory or I/O device           from the given address, direction of            data transfer and synchronization of             data transfer in case of slow devices.

Power Electronic

 Thyristors – Silicon Controlled Rectifiers (SCR’s)

A silicon controlled rectifier or semiconductor-controlled rectifier is a four-layer solidstate current-

controlling device. The name "silicon controlled rectifier" is General Electric's trade name for a type of thyristor

SCRs are mainly used in electronic devices that require control of high voltage and power. This makes 

them applicable in medium and high AC power operations such as motor control function.

An SCR conducts when a gate pulse is applied to it, just like a diode. It has four layers of 

semiconductors that form two structures namely; NPNP or PNPN. In addition, it has three junctions 

labeled as J1, J2 and J3 and three terminals(anode, cathode and a gate). An SCR is diagramatically 

represented as shown below.

The anode connects to the P-type, cathode to the N-type and the gate to the P-type as shown below.

In an SCR, the intrinsic semiconductor is silicon to which the required dopants are infused. However, 

doping a PNPN junction is dependent on the SCR application

Modes of Operation in SCR

 OFF state (forward blocking mode) −                 Here the anode is assigned a positive          voltage, the gate is 

       Nnassigned a zero voltage                              (disconnected) and the cathode is              assigned   a negative voltage. As a 

  result, Junctions J1 and J3 are in forward      bias while J2 is in reverse bias. J2                  reaches its 

     breakdown avalanche value and starts       to conduct. Below this value, the         resistance of J1 is 

    significantly high and is thus said to be        in the off state.

 ON state (conducting mode) − An SCR is        brought to this state either by increasing       the potential 

       difference between the anode and                   cathode above the avalanche voltage          or by applying a positive 

     signal at the gate. Immediately the SCR          starts to conduct, gate voltage is no                longer needed to 

maintain the ON state and is, therefore, switched off by −

      Decreasing the current flow through            it     to the lowest value called holding         current

       Using a transistor placed across the            junction.

 Reverse blocking − This compensates the        drop in forward voltage. This is due to           the fact that a 

      low doped region in P1 is needed. It is          important to note that the voltage                 ratings of forward and 

     reverse blocking are equal.

Power Electronics

  Introduction to power electronics:

            Power Electronics is a field which combines Power (electric power), Electronics and Control systems. 
Power engineering deals with the static and rotating power equipment for the generation, transmission 
and distribution of electric power. Electronics deals with the study of solid state semiconductor power 
devices and circuits for Power conversion to meet the desired control objectives (to control the output 
voltage and output power). Power electronics may be defined as the subject of applications of solid state 
power semiconductor devices (Thyristors) for the control and conversion of electric power. Power 
electronics deals with the study and design of Thyristorised power controllers for variety of application 
like Heat control, Light/Illumination control and Motor control - AC/DC motor drives used in industries, 
High voltage power supplies, Vehicle propulsion systems, High voltage direct current (HVDC) 
transmission. 
Power Electronics refers to the process of controlling the flow of current and voltage and converting it to 
a form that is suitable for user loads. The most desirable power electronic system is one whose efficiency    and reliability is 100%.
                   

     Power electronic applications 

  1.  Commercial applications  Heating                 Systems Ventilating, Air Conditioners,           Central Refrigeration, 

      Lighting, Computers and Office                     equipments, Uninterruptible Power              Supplies (UPS), Elevators, and 

        Emergency Lamps 

2.Domestic applications .Cooking                        Equipments, Lighting, Heating, Air                Conditioners, Refrigerators & 

    Freezers, Personal Computers,                       Entertainment Equipments, UPS

  3. Industrial applications .Pumps,                        compressors, blowers and fans                      Machine  tools, arc furnaces,                           induction 

        furnaces, lighting control circuits,                   industrial lasers, induction heating,               welding equipments 

  4. Aerospace applications .Space shuttle           power supply systems, satellite power          systems, aircraft power 

          systems. 

     5. Telecommunications Battery                          chargers,         power supplies (DC and          UPS), mobile         cell phone battery 

       chargers 

6. Transportation  .Traction control of               electric vehicles, battery chargers for           electric vehicles, electric 

      locomotives, street cars, trolley buses,          automobile electronics including                    engine controls 

7.Utility systems . High voltage DC                      transmission (HVDC), static VAR                    compensation (SVC), Alternative 

      energy sources (wind, photovoltaic),           fuel cells, energy storage systems,                induced draft fans and boiler feed 

     water pumps 

    Types of power electronic                                converters 

1. Rectifiers (AC to DC converters): These converters convert constant ac voltage to variable dc 

output voltage.

2. Choppers (DC to DC converters): Dc chopper converts fixed dc voltage to a controllable dc 

output voltage.

3. Inverters (DC to AC converters): An inverter converts fixed dc voltage to a variable ac output 

voltage.

4. AC voltage controllers: These converters converts fixed ac voltage to a variable ac output voltage 

at same frequency.

5. Cycloconverters: These circuits convert input power at one frequency to output power at a 

different frequency through one stage conversion.