Basic of PCB -2

In previous article, we learn about basics of PCB. 
https://articleelectrical.blogspot.in/2017/12/basics-of-pcb-1.html

In this article, we will see different parts of PCB, material used in PCB and different PCB designing software.

Different parts of PCB

Pad: The pad is a piece of copper. Lead of components are mounted on pad and on which soldering are done. Pad provides the mechanical support to the components.

Silk layer: The silk layer is used for printing line, text or any art on the surface of PCB. It can be used in top and/or bottom layer of PCB. Which is known as silk screen TOP and silk screen BOTTOM. The epoxy ink is used for screen printing. 

Layers: User can choose the layer of PCB according to application. But for choose number of layer user have keep in mind the cost and available space of circuit. The single layer PCB is easy to design and used in routine life and construction of this PCB is simple compare to double layer and multi layer PCB. The double layer PCB or Multi-layer PCB is most prefer compared to single layer PCB cost and available space of circuit for large and complicated circuit. In multi-layer PCB 10-12 layer can be connected. In multi layer PCB most critical thing is to make communicatation between the component in different layer.

Top and bottom layer: All components are mounted in this part of PCB. This layer is green or blue coloured, but it is not a rule you can choose any colour. 
PCB is coated with green colour layer in top and/or bottom layer. This layer is known as solder mask. All components are soldered through the hole and lead of components is known as bottom layer of PCB. 

Trace: The components are not connected with the help of wires in PCB. All components are connected with a conducting material like copper. This copper part of PCB which is used to connect all components that is known as trance.

PCB materials: 
The main material of PCB is dielectric substrate. The dielectric substance is rigid or flexible and this is used according to the application. This dielectric substrate is used with conducting material like copper. The glass epoxy laminates or composite materials are used as dielectric material. 

FR4: FR is stand for FIRE RETARDENT. For all type of PCB manufacturing, most common glass laminated material is FR4. The FR4 is a composite material based on woven glass-epoxy compounds. FR4 is most used dielectric substance because it provides very good mechanical strength.

FR-1 and FR-2: FR1 and FR2 is made up from the paper and phenol compounds. This material is used for only single layer PCB. FR1 and FR2 has similar characteristic. The glass transition temperature is different for both dielectric substance. FR1 has higher glass transition temperature compared to FR2. These material is sub divided in standard, halogen free and non-hydrophobic.

CEM-1: CEM1 is made up from one layer of the paper and two layer of the woven glass epoxy and phenol compounds. CEM-1 can used instead of FR4, but price of CEM1 is higher than FR4. This material is used for Single sided PCB only. 

CEM-3: CEM3 material is white coloured and glass epoxy compound material. This material is mostly used in double layer PCB. CEM-3 has lower mechanical strength compared to FR4. But CEM3 is cheaper than FR4. CEM3 is a good alternative of FR4.

Polyimide: The polyimide is a flexible dielectric substance. So, this material is used in flexible PCB. The polyimide is made up from kepton, rogers and dupont. This material has good electrical properties, felicity, wide range of temperature and high chemical resistance. Working temperature of this material is -200 ͦC to 300 ͦC.

Prepreg: Prepreg is stands for pre-impregnated. Prepreg is a Fibre glass impregnated with resin. These resins are pre-dried. This resin flows, sticks and completely immersed when hetated. The Prepreg has adhesive layer. This adhesive layer gives strength similar to FR4. According to resin content, there are many versions of this material, SR- standard resin, MR- medium resin and HR- high resin. This is chosen according to required thickness, layer structure and impedance. This material also available in high glass transition temperature and halogen free.

PCB designing software:

EAGLE: EAGLE is a most popular and easiest way to design PCB. EAGLE stands for "Easily Applicable Graphical Layout Editor". This software is previously developed by CadSoft Computer and currently Autodesk is developer of this software. EAGLE provides a schematic editor for designing a circuit diagram. 
EAGLE file extension is .SCH
Different parts and components are define in .LBR extension. (Library) 
Board file extension is .BRD

MULTISIM: Multisim is also very powerful and easy learning software. This software is widely used in academic and also in industry for circuit education. This software is originally developed by "Electronics Workbench". Presently this software is a division of "National Instruments (NI)". 

EasyEDA: EasyEDA used to design and simulate circuits. Most important advantage of this software is that, it is web based software and used in browser window. So, this software is independent from OS. This software is an integrated tool for schematic capture. This software provides environment for SPICE circuit simulation and PCB layout. 

Altium Designer: Altium designer is developed by Australian software company "Altium Limited". This is first software which offer 3D visualisation and clearance checking of PCB directly from PCB editor. The main feature of this software is schematic capture, 3D PCB design.

KiCad: KiCAD is developed by "jean-pierre charras". This software has tools to create BoM (Bill of Material), artwork and 3D view of PCB. Many components are available in the library of this software and there is feature that user can add their custom components. This software is support many human languages.

CircuitMaker: Circuitmaker is also developed by "Altium". This software is used to design advanced multichannel and hierarchical schematics. Schematic editor of this software includes basic component placement. All schematic is uploaded to server. These files are available to view by anyone, provided that you need a CircuitMaker account. 

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Types of switches - Electrical switch

In previous article we discussed about mechanical switch:

https://articleelectrical.blogspot.in/2017/12/types-of-switches.html

In this article we will discuss about different types of electrical switch:
Electrical Switches:

The electrical switches is a semiconductor device. These switches are useful compare to mechanical switches because of their low cost, small size and reliability. In this switch, semiconductor materials is used, i.e silicon (Si), germanium (Ge). The electrical switch is used in integrated circuits (ICs), automation, electrical motor drives, HVAC application and also widely used as digital output (DI) of controller. 

               1) Relay

               2) Bipolar transistor

               3) Power diode

               4) MOSFET

               5) IGBT

               6) SCR

               7) TRIAC

               8) DIAC

               9) GTO

1) Relay: The relay is works on the principle of electromechanical, and because of this reason relay is also known as electromechanical switch. When current pass through a coil of relay, magnetic field is induced around the coil. The amount of magnetic field depends on the amount of current passes through the coil. Arrangement of the contacts is done such a way that, if current is increased with curtain limit contacts are energised and change its position. Sometimes, relay uses bi-metallic strip to sense the temperature for safety purpose. Relay are available in wide range of voltage and current. The relay plays an important role in protection against fault in power system network. In industries also, relays are used as a protecting device.

2) Bipolar Transistor: The bipolar transistor has three terminals or lags which is known as base, emitter and collector. The transistor is works on three regions; cut-off region, saturation region and active region. Symbol of the transistor is as shown in below figure. For the switching purpose, active region of the transistor is not used. The transistor enter into saturation region if sufficient amount of current is available at the base terminal. In this region, the current will flow through collector-emitter path and transistor act as a ON switch. If the base current is not sufficient, the circuit will remains open and current cannot flow through the collector-emitter and transistor enters in to cut-off region. The transistor act as OFF switch in cut-off region. The transistors are used as an amplifier in electronics application and it also used to make a gate like AND, OR, NOT in digital circuits and the transistor is also used as a switching device in integrated circuit (ICs). The transistors are not useful in high power application because it has more resistive loss compared to MOSFET.

3) Power diode: The power diode have two terminals which is known as an anode and cathode. The diode is made up of p (positive) and n (nagative) type of semiconductor material and make a pn-junction, which is known as diode. Symbol of power diode is as shown in below figure. When the diode is in forward bias current can flow through the circuit (switch is ON) and in reverse bias blocks current (switch is OFF). If anode voltage is positive with respect to cathode voltage, the diode is in forward bias and act as a ON switch. If he cathode voltage is positive with respect to anode voltage, the diode is in reverse bias and act as a OFF switch. The power diodes are used in power electronics application like, rectifier, voltage multiplier circuit and voltage clamper circuit, etc.

4) MOSFET: MOSFET is stands for Metal Oxide Semiconductor Field Effect Transistor. MOSFET has three lags which is known as gate, drain and source. MOSFET is works on two basic forms; Depletion type and Enhancement type. If gate-source voltage (VGS) is not sufficient, n this condition the MOSFET works in the depletion type. The depletion mode of MOSFET is similar to OFF switch. If gate-source voltage (VGS) is sufficient, MOSFET works as enhancement type and enhancement mode of MOSFET is similar to switch ON. 

5) IGBT: IGBT is stands for Insulated Gate Bipolar Transistor. The IGBT is a combination of BJT and MOSFET. IGBT has a low saturation voltage (characteristic of BJT) as well as  high input impedance and high switching speeds (characteristic of MOSFET) . IGBT has three terminals; Gate, Emitter and Collector. IGBT can control with the use of gate terminal. It can be switched ON and OFF by triggering and disabling its gate terminal. IGBT can block both +Ve and -Ve voltage same as GTO. IGBT is used in the inverter, traction motor control, induction heating and switched mode power supplies.

6) SCR: SCR stands for Silicon Controlled Rectifier. SCR has three terminals; Gate, Anode and Cathode. Working of SCR is same as power diode, The difference is only that SCR start conduction when it is in forward bias (cathode is -ve and anode is +ve) and positive clock pulse at the gate is also required. If clock pulse of gate is zero, SCR turned off by forced commutation in forward bias and in reverse bias SCR is remains in OFF state same as diode. SCRs are used in motor control, power regulators and lamp dimming.

7) TRIAC: TRIAC is same as two SCRs connected in inversely parallel with gate connected. TRIAC is bi-direction device. TRIAC has three lags; Main terminal 1 (MT), Main terminal 2 (MT2) and gate. MT1 and MT2 terminals are connected with circuit which we want to control and gate is available for triggering pulse by positive voltage or negative voltage. When MT2 terminal of TRIAC is at +ve voltage with respect to MT1 terminal and the gate is also +ve triggered, then SCR-1 of TRIAC triggers. Similarly, when MT1 terminal is at positive voltage with respect to MT2 terminal and gate is also +ve triggered, then SCR-2 of TRIAC triggers.

8) DIAC: DIAC is stands for Diode AC switch. The DIAC has two lags. DIAC can operate in both direction so, DIAC is bidirectional switch. The symbol of DIAC is as shown in below figure. DIAC works on two regions; forward blocking or reverse blocking region and avalanche breakover region. When applied voltage is less than breakover voltage DIAC works in forward blocking or reverse blocking region. In this region DIAC act as OFF switch. Avalanche breakdown occurs when applied voltage is greater than the break-over voltage and DIAC act as ON switch. DIAC cannot switch sharply for low voltage and low current application as compared to TRIAC and SCR. DIAC used in light dimming, control of universal motor and heat control circuit.

9) GTO: GTO is stands for Gate Turn-off Thyristor. The GTO has three lags which is known as Gate, Anode and Cathode. As name suggest, this device can turn OFF through gate terminal. In symbol of GTO consists of two arrows on the gate terminal, which shows the bidirectional flow of current through the gate terminal. By applying a small positive gate current GTO can turn ON and turn OFF by negative pulse from the gate terminal. GTO used in inverters, AC & DC Drives, induction heater and SVC (static VAR compensation). GTO cannot use for turning inductive loads off, without the help of the snubber circuit.

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SMPS component and TL494

For introduction of SMPS : 
http://articleelectrical.blogspot.in/2018/02/switched-mode-power-supply-smps.html

TRANSFORMER

A single-phase voltage transformer generally comprises of two electrical coils of wire, into that constructive part one called the “Primary Winding” and another called the “Secondary Winding”. The “primary” side of the transformer as the side that normally takes power and the “secondary” as the side that normally delivers power. In a single-Phase voltage transformer, the primary side with the higher voltage and the secondary side is stepped down the primary voltage

             FIG. High frequency and Multi-secondary transformer

RECTIFIER BRIDGE

l  To transform a AC into DC there are four diodes make configuration which is called a bridge rectifier. The diodes in the bridge circuit supply the same polarity of output for either polarity of input. 

l  Bridge rectifiers are used for converting the alternating current (A.C.) into direct current (D.C.) to use of colloquial appliances. When power comes in through the power lines, the transformer drops it to about 110V to about 3-24V after which, the rectifier converts the current. The bridge rectifier is situated between the capacitors and Transformers.

l  A bridge rectifier is used for converting AC to DC. Cell phones and personal digital assistants (PDA) use AC adapters. Bridge rectifiers are AC adapters

      FIG Bridge Rectifier and symbol

  

CAPACITOR

l  Capacitor is an electronic ingredient that stores electric charge . Capacitor is made by 2 plates which is particularly separated by Dielectric material.

l  One plate compile Positive(+ve) charge and the other plate compile Negative(-ve) charge.

               FIG TYPICAL CAPACITOR                                     FIG CONSTRUCTION OF CAPACITOR 

There are simple form of the capacitor is usually as parallel plate capacitor .it is made up with the two metallaised foil plates at a distance parallel to each other and value of that capacitance in Farads. , being fixed by the surface area of the conductive plates and the distance of separation between them. Altering any two of these values alters the the value of its capacitance and this forms the basis of operation of the variable capacitors.

Design Equation

       TABLE: Design Equation relation

Pin Configuration and Functions of TL494 

                           

          FIG : IC TL494 Pin configuration and Pin connection

TL494 Features

Ø  Output Control Selects Single-Ended or Push-Pull Operation

Ø  Internal Circuitry Prohibits Double Pulse at Either Output

Ø  Variable Dead Time Provides Control Over Total Range

Ø  Internal Regulator Provides a Stable 5-V Reference Supply With 5% Tolerance

Ø  Circuit Architecture Allows Easy Synchronization

Ø  Uncommitted Outputs for 200-mA Sink or Source Current

Principle Of Operation

u  The TL494 is a fixed-frequency pulse-width-modulation (PWM) control circuit.

u  Modulation of output pulses is accomplished by comparing the sawtooth waveform created by the internal oscillator on the timing capacitor (CT) to either of two control signals.

u   The output stage is enabled during the time when the sawtooth voltage is greater than the voltage control signals.

u  As the control signal increases, the time during which the sawtooth input is greater decreases; therefore, the output pulse duration decreases.

u  A pulse-steering flip-flop alternately directs the modulated pulse to each of the two output transistors.

u  Figure shows the relationship between the pulses and the signals.

u  The control signals are derived from two sources: the dead-time (off-time) control circuit and the error amplifier.

Applications Of  IC TL494

Ø  Desktop PCs

Ø  Microwave Ovens

Ø  Power Supplies : AC/DC

Ø  Solar Micro Inverter

Ø  Smoke Detector

Ø  Solar Power Inverter

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Switched-mode power supply (SMPS)

Block Diagram and description

                                   FIG: BLOCK DIAGRAM OF SWITCH MODE POWER SUPPLY

Input Rectifier Stage

It is used to convert an AC input into DC. A SMPS with dc input does not require this stage. The rectifier produces unregulated dc which is feed to the filter circuit.

Inverter Stages

      The inverter stage converts DC, whether directly from the input or from the rectifier stage specified as, 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(KHz).

Output transformer:

          If the output required is to be isolated from input, the inverted AC is used to draw the

primary windings of a high frequency transformer. This converts the voltage up or down to the required output level on it’s secondary winding.

Output rectifier:

          If the dc output is required, then the ac output from the transformer is rectified.

Regulation:

         Feedback circuit monitor the output voltage and compare it with the reference voltage.

Multiple output block

  

            FIG: CONFIGURATION OF MULTIPLE OUTPUT CONCEPT

n  For the regulating switched mode power supply there are possible multiple output voltages are getting with either proper arrangement of transformer turns ratio or ideal switching of the MOSFETs. Which is situated in the fig. Of Primary portion.

n  Where as output voltages are possible at the other secondary portion of the circuit configuration. So, the help of low pass filter with assembled with inductor and capacitor are make connected across the load

Advantages and Disadvantages of SMPS

n  The main advantage of this method has great efficiency because the switching transistor dispel little power when it is outside of its active region (i.e., when the transistor acts like a switch and either has a negligible voltage drop transverse it or a negligible current through it)

n  Other advantages include smaller size and lighter weight (from the exclusion of low frequency transformers which have a high weight) because low heat dissipation and reduces the harmonic.

n  Disadvantages include greater complexity, the generation of high-amplitude, high-Frequency energy that the low-pass filter might block to procrastinate electromagnetic interference (EMI), Ripple Voltage at the switching frequency.

n  The Harmonic Frequencies thereof, very low cost SMPS may couple electrical switching noise back onto the mains power line, that causing interference with A/V equipment connected to the same phase. Non-power-factor-Corrected SMPS also reason harmonic distortion.

APPLICATION

  

n  Switched-mode power supply units (PSU) are used in PLCs, Audio and Video applications, measuring instruments, security systems, and machine and tools industries.

n  In domestic products such as personal computers often have universal inputs, meaning that They can accept power from mains supplies throughout the world, nevertheless a manual voltage range switch may be required.

n  Switch -mode power supplies can tolerate a wide range of power frequencies and voltages.

For SMPS components and TL494,

https://articleelectrical.blogspot.in/2018/02/smps-component-and-tl494.html

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BJT (Bipolar Junction Transistor)

In this article, we will discuss about the bipolar junction transistor, which is also known as BJT. The BJT is a solid-state device and used for amplifying, controlling and generating electrical signals.

What is the meaning of “bipolar”? Bipolar word is used because of the current through the BJT is by both the carriers; the electrons and the holes. The junction stands for, inside the BJT, there is PN junction and Transistor is stands for transfer of resistance.

Construction:

The transistor has three terminals; emitter (E), base (B) and collectors (C).

There are two types of transistors;

              1)      NPN transistor

              2)      PNP transistor

      Symbol:

1)  NPN transistor: In this type of BJT, three regions are used; one P region and two n region. P region is sandwich between two N regions. Here, emitter and collector are connected with N type of region and base is connected with P type region. The base terminal is always lightly doped and thin area. The collector terminal is highly doped and wide area.

As shown in above figure, there are three types of current; emitter current (IE), base current (IB), and collector current (IC). As we discuss earlier, base is lightly doped and thin, value of base current is very low (in terms of micro-amps). The value of collector current and emitter current is nearly equal. By the above figure, we can say that, the collector current is addition of the base current and the emitter current.

2)  PNP transistor: In this type of BJT, two P type of region and one n type region is used. The collector and emitter terminal of transistor is connected as P reigon and the base region is connected as N type region.

As shown in above figure, the emitter current is addition of the base current and the collector current.

Configuration:

Transistor has three terminals. With respect to these terminals, transistor can use with common emitter, common base and common collector configurations. The basic two configurations are common emitter and common base. By this configuration, we can define current gain of transistor. Current gain is defined as ratio of output current and input current.

For common emitter configuration, the output current is IC and the input current is IB. so, gain is IC/IB and it is denoted as α.

For common base configuration, the input current is IE and the output current is IC. So, gain is IC/IE and it is denoted as β.

Modes of operation;

The transistor will work on three regions;

                1) Active

a.       Forward active

b.       Reverse active

                2) Saturation

                3) Cut-off

Mode	NPN	PNP	Feature	Usage
Cut-off	Reverse	Reverse	No current	Switch
Forward active	Forward	Reverse	Voltage controlled current	Amplifier
Saturation	Forward	Forward	Low resistance	Switch
Reverse active	Reverse	Forward	Voltage controlled current	Usually not used

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