Saturday, May 18, 2019

Capacitor


Capacitors are most frequently used component in electronic circuits. Whatever types and values a selection of correct capacitor solves many circuit issues. In this article we will discuss definition of capacitor, capacitor symbol, principle of capacitor, capacitor unit and capacitor working.

What is a Capacitor?

Capacitors are electronic components which can momentarily store electrical charge, and whose working is determined by how much electric charge can be stored in it.

Capacitor
Different Types of Capacitors
A capacitor is an electronic component having two terminals. Capacitor is a passive component. Capacitor stores electric energy. Capacitance we can define as the effect of a capacitor. Sometimes it is called as a condenser or condensator.

Capacitance

The effect created by a capacitor is known as capacitance. Also we can define the capacitance as the ratio of the electric charge on each conductor to the potential difference between.

In other words we can say that, the capacitance is defined as the ratio of charge Q on a conductor to a potential difference V between them.

C=Q/V

Capacitor Unit

The unit of capacitance is the Farad (F) which is the International System of Units (SI). In general electronics, ranges from 1 picofarad (pF) to 1 millifarad (mF) capacitance values are used.

Capacitor Symbol

Capacitor
Capacitor Symbols
First is fixed capacitor i.e. non polarized capacitor and this capacitor can be used in both AC and DC circuit. This capacitor is “bilateral element” i.e. polarity doesn't matter during connection.

Second is varying capacitor. Here capacitance can be vary.

Third is polarized capacitor. During its connection here we have to take care of its polarity. This capacitor is use in a DC circuit.

Principal of Capacitor

Below points will explain the principal of capacitor in detail;

  • Most of the capacitors have at least two electrical conductors’ i.e. metallic plates, in other words we can say that outsides parted or separated by a dielectric medium.
  • These conductors are may be a thin film, a foil, sintered bead of metal or a part of electrolyte.
  • The capacitor's charge capacity is increase by the non-conducting dielectric material.
  • Dielectric materials in capacitors are commonly used as paper, plastic film, glass, mica, ceramic, cellulose, porcelain, Mylar, Teflon and layers of oxide. Sometimes air also used as non-conductive medium.
  • When a potential difference like DC voltage from battery is applied across the two conductors, an electric field grows across the dielectric material, producing a positive charge to gather on one plate and negative charge to gather on the other plate of capacitor.
Capacitor
Dielectric in ceramic disc capacitor
  • Dielectric never allows current to flow across it. Though, there is a flow of charge through the applied source circuit. If this state is continued adequately for long, the current through the applied source circuit ends.
  • If a varying voltage is applied across the two leads of the capacitor, the applied source undergoes an on-going current because of the charging and discharging cycles of the capacitor.
  • Capacitor didn’t dissipate power in the form of heat.

Capacitor working

Below points will explain the working of capacitor in detail;

  • The working of capacitor based on Coulomb’s law. A charge on one conductor employs a force on the charge carriers in the other conductor, enticing opposite polarity charge and deterring like polarity charges, thus an opposite polarity charge will be made or induced on the surface of the other conductor.
  • When supply is applied from a battery or a power supply, there is flow of current i.e. flow of electron will occur. But there is a dielectric medium in capacitor which stops the flow of current between the plates. So these electrons will start gathering on the plates. Up to a definite level, the charge can be deposited or stored. This shows that the capacitor is charged fully.
  • The two plates in capacitor have an equal amount of positive and negative charges producing a strong electric field which makes them to hold this charge inside the capacitor.
  • If the capacitor is fully charged and if the load is connected to a capacitor, it will supply energy to load until it converts to electrically neutral.
Let understand working of capacitor with the help of below figure;

Capacitor
Capacitor working
  • A battery (DC Source) is connected across a capacitor i.e. one surface of the capacitor which is named as plate 1 gets positive end of the battery and another surface i.e. second surface of the capacitor which is named as plate 2 gets negative end of the battery.
  • With the application of battery or DC voltage, the full voltage of the battery is applied across the capacitor. At this condition, plate 1 of capacitor is in positive energy with respect to the plate 2.
  • Current from the battery or DC supply source tries to flow through the capacitor from its positive plate (plate 1) to negative plate (plate 2) but cannot flow with large amount because these plates are separated with a dielectric insulating material.
  • Somewhat a very small current will flow through this dielectric insulating material from Positive side plate to Negative side plate, which depends on the value of strength of this dielectric material.
  • Now an electric field will generate or form inside the capacitor i.e. inside the dielectric from positive plate to negative plate.
  • As the time passes, the positive plate (i.e. plate 1) will gather positive charge from the battery or DC source and negative plate (i.e. plate 2) will gather negative charge from negative side of the battery or power source.
  • After a certain time, the capacitor carries maximum quantity of charge according to its capacitance with respect to the applied voltage. This time duration is called as charging time of the capacitor.
  • If two sides of capacitor (i.e. plate 1 and plate 2) get shorted through a load i.e. a load is connected across the plates, a current will flow across the load from plate 1 to plate 2 until all the charges get disappeared from both the plates. This time duration is called as the discharging time of the capacitor.
Capacitor
Electrolytic Capacitors assembled in a circuit


Conclusion

Capacitors are most frequently used component of the electronic circuits. Nearly all types of circuits have its presence. There are many types of capacitors and mostly used in electronic circuits for blocking DC while allowing AC to pass and also used for energy storage.

Saturday, May 4, 2019

LDO


Linear regulators are a gainful means to supply a steady and regulated output voltage, with the design easiness and few external components in the circuit. If the output current is less than few amps and the output voltage is near to that of the input, LDO’s deliver the best cost-performance.

Full form of LDO is, “Low-Dropout linear regulators”.

LDO
Low-Dropout linear regulators
An LDO is a linear voltage regulator intended to work with a very low input-to-output voltage differential (dropout voltage) in order to reduce the power dissipated as heat on the device and rise conversion efficiency. In other words we can say that, a low-dropout or LDO regulator is a DC linear voltage regulator that can control the output voltage even when the supply voltage is very near to the output voltage.

As compare to DC-DC switching converters, LDO regulators do not produce ripple, therefore they gives a ripple free supply voltage, and need few design steps.

Advantages of LDO

The advantages of a low dropout voltage regulator over other DC to DC regulators contain the non-availability of switching noise (as no switching takes place), reduced device size (as inductors or transformers are no required), and better design ease (usually includes a reference, an amplifier, and a pass element).

Disadvantages of LDO

The disadvantage is that, unlike switching regulators, linear DC regulators dissipate power, and thus heat in order to regulate the output voltage.

LDO architecture

The LDO explanation starts with the dropout voltage, which is the minimum voltage required through the regulator to keep maintain the regulation. For example, a 3.3 V LDO regulator with 1 V dropout will need a minimum input of 4.3 V. To know the meaning of voltage drop across the LDO, let’s look at the essential LDO architecture with a pass element. As shown in below figure, the pass element can be an N- or P-channel FET, which delivers the voltage drop as a function of FET’s on-resistance, RDS(on).
LDO
Basic LDO block diagram
The main components in LDO are; a power FET and a differential amplifier (also called as error amplifier). One input of the differential amplifier monitors the part of the output determined by the externally connected resistor ratio of R1 and R2. The second input to the differential amplifier is from a steady voltage reference (also called as bandgap reference). If the output voltage increases too high comparative to the reference voltage, the gate drive voltage to the power FET changes, to keep a constant output voltage.

LDO
Pass element can be an N- or P-channel FET in a LDO

Key LDO Performance Parameters

1)  Dropout Voltage – It is defined as the difference between the input and output voltages at the point when an additional or more decrease in input voltage causes output voltage regulation to become fail. In the dropout situation, the pass element works in the linear region and acts like a resistor. For the modern LDO, the pass element is normally implemented with PMOS or NMOS FETs, which can attain a dropout voltage as low as 30mV to 500mV.

2)  Load Regulation – It is defined as the output voltage variation for a given load variation. This is normally from no load to full load. It can be expressed by below equation;

Load regulation = ΔVout/ΔIout = (Vout@noload – Vout@fullload)/(0 – Iout_fullload)

Load regulation specifies the performance of the pass element and the closed-loop DC gain of the regulator. The higher the closed-loop DC gain, the superior is the load regulation.

3)  Line Regulation – It is the output voltage variation for a given input voltage variation. It can be expressed by below equation;

Line regulation = ΔVout/ΔVin = (Vout@vin_max – Vout@vin_min)/(Vin_max – Vin_min)

4)  Power Supply Rejection Ratio (PSRR) – It is a sign of the LDO’s capacity to reduce fluctuations in the output voltage produced by the input voltage, as expressed in below equation. While line regulation is only measured at DC, PSRR measured over a wide frequency range.

PSRR = 20log₁₀(Vin/Vout)

Consider a conventional closed-loop system, the small-signal output voltage, ͠Vout can be expressed as;

Vout = {[Gvg/(1 + kv X Gc X Goc)] ͠Vin} + {[(Gc X Goc)/(1 + kv X Gc X Goc)] ͠Vref}

Where;

͠Vin = the small signal input voltage

Gvg = the open-loop transfer function from input to output voltage

Kv = the output voltage sensing gain

Gc = the compensator’s transfer function

Goc = the open-loop transfer function from the control signal to the output voltage

kv X Gc X Goc = is the closed-loop transfer function, T(s)

While seeing above two equations of PSRR, it is clear that the PSRR contains the closed-loop gain, T(s), and the inverse of the open-loop transfer function from input to output voltage, 1/Gvg, as shown in below figure. However the closed-loop transfer function controls at lower frequencies, the open-loop transfer function from input to output voltage controls at higher frequencies.

LDO
PSRR vs Frequency
5) Noise – It is normally states to the noise on the output voltage produced by the LDO itself, which is a natural characteristic of the bandgap voltage reference. Second equation of PSRR (see PSRR) expresses the relation of reference voltage to the output voltage. Inappropriately, the closed-loop transfer function is not operative for removal of the noise from the reference voltage to the output voltage. So, most low-noise LDOs require an extra filter to avoid noise from entering the closed-loop.

6) Transient Response – LDOs are generally used in applications where point-of-load regulation is essential, such as supplying power to digital ICs, FPGAs, DSPs and low-power consuming CPUs. The load in such applications has many modes of operation, which need different supply currents. As a result, the LDO has to react fast to keep the supply voltage within the requisite levels. This makes the transient performance of an LDO one of the critical performance parameters. As in all closed-loop systems, the transient response mostly relies on the bandwidth of the closed-loop transfer function. To attain the best transient response, the closed-loop bandwidth has to be very high while confirming enough phase margin to keep stability.

7) Quiescent Current – It is also called as ground current. The quiescent current of an LDO is the arrangement of the bias current and the drive current of the pass element, and is usually kept as low as possible. Moreover, when PMOS or NMOS FETs are used as the pass element, the quiescent current is moderately unaffected by the load current. Since the quiescent current doesn’t pass through to the output, it effects the LDO’s efficiency, which can be calculated by below equation;

Efficiency = (Iout X Vout) / (Iout + Iq) X Vin

The power dissipation inside the LDO is given by: Vin X (Iq+Iout) – Vout X Iout. To enhance the LDO’s efficiency, both quiescent current and the difference between the input and output voltages must be reduced. The difference between the input and output voltages have a direct effect on efficiency and power dissipation, so the lowest dropout voltage is usually chosen.

Applications of LDO

LDOs are mainly suitable to applications that need an output voltage regulated to somewhat below the input voltage. While buck and boost converters have restrictions on the maximum/minimum duty cycle, their output voltage will lose regulation with an input voltage that is near to the output voltage.

Even though an LDO cannot supply high efficiency power conversion as compare to a switch mode power supply (SMPS), it is still a essential voltage regulator for many new applications. In noise sensitive applications, it is very hard for an SMPS to attain the essential output ripple to meet a tight noise requirement. Therefore, it is not unusual for an LDO to be adding as an active filter to the output side of a SMPS. For using LDO at output side of the SMPS, please keep in mind that LDO must have high PSRR at the SMPS switching frequency.

Conclusion

LDO perform a vital function in system power design and supplies power to many IC’s. An LDO is usually supposed as a simple and cheap way to regulate and control an output voltage that is supplied from a higher input voltage supply. Cost and ease are the only reason for their extensive use. To make the best use of an LDO, it is required to know the main performance parameters and their effect on given loads.

Wednesday, January 16, 2019

Linear Voltage Regulator


Voltage Regulator

Voltage Regulator takes an input voltage and creates a regulated output voltage irrespective of the input voltage at either a fixed voltage level or adjustable voltage level. In simple words, a voltage regulator is used to regulate voltage level.

Types of Voltage Regulators

There are mostly two types of voltage regulators: first one is Linear voltage regulators and the second are switching voltage regulators. Here let’s discuss Linear Voltage Regulator;

Linear Voltage Regulator

A linear voltage regulator delivers a steady output voltage from a more or less steady input voltage source. In normal operation, even if the input voltage varies fast, the output voltage remains steady. This means they can also very efficiently filter out input ripple, not only at the fundamental frequency, but also for fifth or tenth harmonic. The constraint is only the response speed of the internal error amplifier feedback circuit.
7805
7805 Pinout Diagram
Most linear regulators have a closed loop control for voltage regulation, below figure shows it;
Linear Regulator
Linear Regulator Block Diagram

Linear Voltage Regulator working

  • The pass transistor is the regulatory element, efficiently a variable resistor that controls the current flowing from input to output.
  • The resistor divider Ra/Rb is chosen so that at the required output voltage, the divided down voltage at the error amp inverting input is the same as the Vref voltage at the non-inverting input.
  • The error amplifier controls its output in a way that the voltage variance between its inputs is always zero.
  • If the voltage at the output rises due to a drop in the load or an increased input voltage, the voltage at the inverting input of the error amplifier increases higher than Vref voltage and the output of the error amplifier goes negative, so decreasing the drive to the pass transistor and reducing the output voltage. 
  • If the load rises or the input voltage falls, the voltage at the inverting input drops below the Vref voltage and the drive to the transistor is increased to raise the output voltage to compensate.
  • Therefore the same feedback loop controls for both input voltage differences (line regulation) and changes in load (load regulation).
  • If the output is shorted to ground, the transistor would be turned ON hardly and a very high current would flow from input to output, so a second internal circuit is needed to limit the current.
Below figure shows the Linear Regulator with current limiting;
Linear regulator with current limiting
Linear regulator with current limiting

  • The sense resistor, Rs is used for the current limiting which uses the voltage drop across to monitor the output current. When the current is high enough so that the voltage exceeds 0.7V, transistor Q2 starts to conduct to take current away from transistor Q1, thus decreasing the drive and limiting the output current, thus Ilimit = 0.7V/Rs.
  • The current limit needs to be set well above the maximum current that would flows during usual process. Normally the limit is 150% - 200% greater than the rated current. As the regulator is not deactivated during a short circuit, it is in constant overload.
  • The dissimilarity between input and output voltage is dropped by the pass transistor. If the input voltage is 12V and the regulated output voltage is 5V, then 7V has to be dropped by the transistor.
  • This means more power is dissipated in the regulator ac compare to actually deliver to the load. This is the reason why many linear regulators require a heat sink.
  • If in the case the input voltage drops below the output voltage, the linear regulator cannot compensate and the output voltage will follow the down input voltage.
  • If the input voltage drops too low, the internal power supply to the error amplifier and Vref will be compromised and output may become unbalanced or start to fluctuate.
  • Linear regulators also execute poorly in stand-by mode. In the case of no load, a usual 78xx series regulator needs around 5mA to power the error amp and its reference voltage circuits.
  • The advantages of linear regulators are low price, good control features, it has low noise and it has low emissions and outstanding transient response.
  • The disadvantages are high quiescent consumption and very low efficiency for large input/output voltage changes.

Efficiency of a Linear Voltage Regulator

The efficiency of linear regulator is defined by the ratio of the supplied output power Pout to the power consumption Pin.

η = Pout/Pin

Where;
Pout = Vout x Iout
Pin = Vin x Iin
Iin = Iout + Iq

Iq is the quiescent current of the linear regulator which is measured at under no-load conditions. The equation can be rewritten as;

η = (Vout x Iout) / Vin(Iout + Iq)

The voltage regulator has to be equipped with a large sufficient heat sink to permit safe operation under the worst-case circumstances of maximum input voltage and maximum output current.

Problems with Linear Voltage Regulator

Linear regulators have a number of advantages on the one hand, but also have some disadvantages that require special precaution in their use.

Drop out problem with Linear Regulator
Drop out problem with Linear Regulator
As stated before, if the voltage difference between input and output is below the required range (typically 2V), then the regulation loop can no longer work correctly. A common application problem arises when a rectified AC input has a high voltage ripple because the smoothing capacitor is too small as shown in below diagram. If the input voltage falls below the fall-out voltage on each half cycle, then the regulated output will show periodic dips at twice the mains frequency. These quick dips will not show up on a multimeter which just measures the normal output voltage, but can cause circuit problems. This effect can be removed by either using bigger smoothing capacitors or increasing the turn’s ratio of the transformer.

Linear Voltage Regulator circuit diagram

Below circuit diagram shows a type of Voltage Regulator i.e. Linear Voltage Regulator;
Linear Voltage Regulator
Linear Voltage Regulator Circuit Diagram

Application of Linear Voltage Regulator

  • Voltage regulators are found in devices such as computer power supplies where they stabilize the DC voltages used by the processor and other circuit elements. For example, it takes in 90V-240V and provides 12V, 5V, 3.3V, -12V for the system to run and for the laptop the output voltage of the power adapter is about 19-20V.
  • In automobile alternators and central power station generator plants, a voltage regulator regulates the output of the plant.
  • In an electric power distribution system, voltage regulators may be mounted at a substation or along supply lines so that all customers get stable voltage independent of how much power is drawn from the line.
  • Mobile phone charger, it takes in 100V-240V (AC/DC) and will give you a stable 5V DC output. If the input voltage stays within the range the output will continually be the same.
  • We are using micro-controllers everywhere and mostly all micro-controller runs on 5V and a very low current so in most cases a 7805 is placed with them to make sure that the controller runs correctly.
  • Any sensitive electronic device that needs steady input voltage is most of the time supplied by a regulator.
  • For AC voltage regulator we can use the voltage stabilizer that takes input a somewhat fluctuating voltage and provides a stable AC voltage. These types of regulators are usually used with freezers and televisions.

Conclusion

Voltage regulators like Linear Regulator are a great select for powering ON very low powered devices in which the difference between the input and output is small. They are easy to use, simple and cheap, a linear regulator is usually incompetent.

Sunday, January 13, 2019

Interleaved Power Factor Correction


Power Factor we can define as the ratio between the useful (true) power (kW) to the total (apparent) power (kVA) consumed by a circuit. It is a measurement of how proficiently electrical power is converted into useful power which can be further use for output load.

More on Power Factor you can find in my previous article at below link;
"What is Power Factor and Why is it important?"

There are many methods for Power Factor Correction and Interleaved Power Factor Correction is one of them. Other Power Factor Correction methods you can find in my previous article at below link;
"Types of Power Factor Correction"


What is Interleaved Power Factor Correction?

A usual single-stage PFC controller design on a large inductor and requires extensive filtering to reduce high-frequency ripple. An alternative topology replaces the single PFC boost converter with a two interleaved converters each operating 180° out of phase.

This interleaved method very much reduces the high-frequency ripple of the input current and as well as the current into the output capacitor of the PFC pre-regulator. The arrangement of reduced ripple and lower average current in each phase allows use of a smaller inductor size and input – output capacitor as compare to single-phase design. Component size is one of the main reasons for implementing an Interleave PFC design.

Below figure shows,”Interleaved Transition Mode PFC using UCC28063”;

Interleaved Transition Mode PFC
Interleaved Transition Mode PFC using UCC28063
As we can see in the figure an interleaved PFC consists of a two boost converter sharing the same load capacitor. As we can see in the figure, if we have the same inductance for each boost converter, we can see that the energy stored by this PFC system is doubled.  An output power capability of this PFC system is determined by energy stored in the inductor. By an Interleaved PFC with much smaller inductor having lower inductance values for a given power rating, the output power can be generate same like single stage PFC.
     
Interleaved PFC arrangement consists of;
·     Two inductors; which is used for energy storage.
·      Load balancing controller; which is used to make sure energy should be distributed equally i.e. the load balancing controller balances the variation in inductance values or feedback circuits.
·       Feed-Forward controller; which control sudden input voltage changes.
·      Voltage error controller; the dc output voltage and corresponding reference are applied to this controller to avoid the load variations so that output voltage should not vary.
·      Current error controller; which controls phase and shape of the input current which is the sum of both the inductor current. The output of this controller is PWM which is used to drive MOSFETS.
·       Load balance loop; which controls current through both the inductor. It generate corrected PWM term, which is subtracted from first PWM to get the final duty cycle of the first boost converter, and it is added to second PWM to find out the balanced duty cycle of the second boost converter.
·      PI controller; which controls unbalanced current flowing through two inductors by regulating this error and by adjusting the MOSFETs duty cycles.

Interleaving power converters can lower conduction losses and improves the overall system efficiency.


Conclusion

Two double energy storing capacity of PFC system, "Interleaved Power Factor Correction" is the best method. Also, for high energy application by this method we can reduce the size of Inductor and capacitor.

Friday, January 4, 2019

RoHS and WEEE for e-Waste


Electronic waste or e-waste defines rejected electrical or electronic devices or equipment’s. The process of disassembling and placing of electronic waste in developing countries causes a number of environmental effects. These hazardous elements from e-Waste affect the water, soil and air. Government considered this situation as serious matter and came with two regulations for e-Waste i.e. RoHS and WEEE for e-Waste.

Let learn more about these in detail;
RoHS and WEEE for e-Waste
RoHS and WEEE for e-Waste

e-Waste

  • Electronic waste or e-waste may be defined as rejected computers, electronic equipment for office, entertainment electronic devices, cellular phones, television sets, refrigerators and other household electronic equipment’s.
  • This e-waste contains used electronics equipment’s which are meant for reuse, resale, retrieve, recycling, or discarding and secondary leftovers like; copper, plastic, steel, etc.
  • The word "waste" means remains or material of equipment’s which is discarded by the consumer rather than recycling those materials. 
  • E-waste or electronic waste is generated when an electronic product is thrown away after the end of its valuable life.
  • The fast progression of technology means that a very huge quantity of e-waste is generated daily.
  • More gadgets, more users and quicker device replacement have contributed to the development of e-waste.
  • Contact from unsuitable e-waste handling has been linked to many health concerns.
RoHS and WEEE
Electronic Waste
To tackle above issues generated by e-waste, many law agencies or directive creators or government decided to make some rules and regulations, which they termed as RoHS and WEEE. Let’s discuss these in detail;

RoHS

RoHS stands for "Restriction of Hazardous Substances". RoHS, is also called as Directive 2002/95/EC, created in the European Union and which controls the use of specific harmful materials found in electrical and electronic products or equipment’s.

More details on RoHS you can find in our previous article. Please click below link to know more;

"RoHS and RoHS Substances"

WEEE

Full form of WEEE is “Waste Electrical and Electronic Equipment”. Objective of WEEE compliance is to boost the design of electronic equipment’s by keeping environmentally safe, recycling and recovery in mind. RoHS compliance comes together with WEEE by reducing the amount of hazardous chemicals used in electronics manufacturing.

RoHS controls the hazardous substances used in electrical and electronic equipment’s, while WEEE controls the discarding of this same electrical and electronic equipment’s.

Let see WEEE in more detail;
  • This European law applies to an extensive range of electronic and electrical equipment’s.
  • WEEE boosts the collection, treatment, recycling and retrieval of waste electrical and electronic equipment’s. It applies to a vast range of products, and inspires and sets standards for the collection, treatment, recycling and recovery of waste electrical and electronic equipment’s.
  • Waste of electrical and electronic equipment (WEEE) such as computers, TV-sets, fridges and cell phones is one the fastest growing waste products in the European Union.
  • To address environment related problems, two parts of legislation have been put in place: The Directive on waste electrical and electronic equipment (WEEE Directive) and the Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment (RoHS Directive).
  • The Waste Electrical and Electronic Equipment Directive (WEEE Directive) is the European Community Directive 2012/19/EU on waste electrical and electronic equipment which, together with the RoHS Directive 2011/65/EU, became European Law in February 2003 and aims to minimize the impacts of electrical and electronic equipment on the environment during its lifetime and when it becomes waste.
  • The first WEEE Directive (Directive 2002/96/EC) come into the force in February 2003. The Directive delivered for the formation of collection arrangements where consumers return their WEEE free of cost. These arrangements aim to rise the recycling of WEEE or re-use of the products and components.
  • In December 2008, the European Commission planned to review the Directive in order to control the very fast growing waste products. The new WEEE Directive 2012/19/EU come into force on 13 August 2012 and became operative on 14 February 2014.
  • European Union regulation which limits the use of hazardous substances in electrical and electronic equipment’s (RoHS Directive 2002/95/EC) comes into the force in February 2003. The regulation requires hazardous materials such as lead, mercury, cadmium, and hexavalent chromium and flame retardants such as polybrominated biphenyls (PBB) or polybrominated diphenyl ethers (PBDE) to be replaced by harmless replacements. In December 2008, the European Commission planned to review the Directive.
  • European Union regulation limiting the use of hazardous materials in electrical and electronic equipment (EEE) and encouraging the collection and recycling of such equipment’s has been in force since February 2003.
  • Further the necessities for selective treatment for materials and components of Waste of Electronic and Electrical Equipment (WEEE), the WEEE Directive and national law/regulation on WEEE force member states to create and keep a registry of producers putting electrical and electronic equipment’s into the market.
  • The WEEE Directive covers the use of WEEE for both, consumers and professional purposes;
  1. Private consumers will be able to return their WEEE to collection services free of charge.
  2. Producers (includes; manufacturers, sellers, distributors) will be liable for taking back and recycling electrical and electronic equipment’s.
  3. Producers have to necessary attain a sequence of recycling and recovery objectives for different categories of electrical and electronic equipment’s.
  • The WEEE Directive needs that Member States confirm a objective, by the date 31 December 2006, of at least 4 kilograms of WEEE per resident per year is being collected from private household consumers.
  • The WEEE directive sets a total of 10 groups of WEEE for reporting purposes;
  1. Large household appliances
  2. Small household appliances
  3. IT and telecommunications equipment’s
  4. Consumer equipment’s
  5. Lighting equipment’s
  6. Electrical and electronic tools
  7. Toys, leisure and sports equipment’s
  8. Medical devices
  9. Monitoring and control instruments and equipment’s
  10. Automatic dispensers
  • The following products are exempted or out of range of WEEE;
  1. Implanted and Infected equipment’s
  2. Large Scale Stationary Industrial Tools and equipment’s
  3. Military equipment’s
  4. Automotive equipment’s
  5. Aerospace/Aircraft equipment’s
  6. Surface Transportation equipment’s

WEEE Symbol

The symbol accepted by the European Assembly to symbolize waste electrical and electronic equipment contains a crossed-out wheelie bin with or without a single black line below the symbol. The black line shows that products have been placed in the market after the year 2005, when the Directive came into force. The products without the black line were manufactured between the year 2002 and the year 2005, in such cases, these are treated as "Historic WEEE" and fall outside compensation via manufacturer compliance systems.

The WEEE symbol must be positioned on an EEE product if the product falls in one of the 10 groups and is placed into the European Union market after the date 13th August 2005. The product is treated as "new WEEE”. Manufacturers must deliver refurbishment, treatment and reuse information for each "new WEEE”.

Below are the images of both the types of symbols;
WEEE
WEEE Symbol without black line
WEEE
WEEE Symbol with black line

Conclusion

The regulation like WEEE offers the creation of collection arrangements, where customers return their used waste related to Electrical and Electronics free of charge. The aim of these arrangements is to increase the recycling and/or re-use of such products. On the other hand the regulation like RoHS limits the use of hazardous substances in electrical and electronic equipment’s. Both are playing an important role to tackle the issue of e-waste and encouraging us to keep safe our environment.

Friday, December 28, 2018

RoHS and RoHS Substances


What is RoHS?

RoHS is a directive that was legitimately accepted in July 2006 by the European Union (EU), for the purpose of defending both people and the environment from harmful chemicals found normally in electronics and electrical products.

Main aim of RoHS is to reduce the hazardous elements that are faced in everyday life and which affects our ecosystem.

The use of the RoHS directive is not only related to apparatus manufactured in the European Union, it also relates to items imported in European Union.

RoHS full form

RoHS full form is, “Restriction of Hazardous Substances”.

What is RoHS 1 and RoHS 2?


RoHS 1

The RoHS 1 directive took effect on 1 July 2006, and is compulsory to be imposed and became a law in each EU member state.

This directive limits (with exclusions) the use of six hazardous materials in the manufacture of many types of electronic and electrical equipment and components.

It is thoroughly related with the Waste Electrical and Electronic Equipment Directive (WEEE) 2002/96/EC which sets collection, recycling and recovery objectives for electrical goods and is part of a statutory initiative to solve the difficulty of vast amounts of toxic or poisonous electronic waste.

RoHS is frequently states to the European Union standard, unless otherwise qualified.

RoHS 2

The RoHS 2 directive (2011/65/EU) is a development of the original directive and became law on 21 July 2011 and took effect 2 January 2013.

It talks about the same substances as the original directive while refining regulatory situations and legal simplicity.

It needs periodic re-evaluations that simplify regular expansion of its requirements to cover extra electronic and electrical equipment, cables and spare parts. The CE logo now designates compliance and RoHS 2 declaration of conformity.

RoHS logo

RoHS did not need any particular product marking, but many companies have implemented their own compliance marks to decrease confusion. Below are some examples of RoHS logo's;

RoHS Symbol

RoHS Symbol

RoHS Symbol

RoHS Symbol

RoHS Symbol

Chinese RoHS marking consist of a lower case "e" within a circle with arrows.

Chinese RoHS Symbol
Chinese RoHS Symbol

RoHS Substances

RoHS is frequently stated as the "lead-free directive", but it restricts the use of the following ten substances:

1) Lead (Pb) - Lead mainly used in the making of batteries, televisions and computer monitors. RoHS restricts on the use of lead to 1000ppm.

2) Mercury (Hg) - Mercury has been used in the production of fluorescent lamps, hig and low pressure mercury- vapor lamps, printed circuit boards, aluminum electroplating, thermostats and fuel cells. The RoHS directive restricts the use of mercury to 100ppm.

3) Cadmium (Cd) – Cadmium used as a stabilizer for some plastics, also used in cadmium/nickel batteries, electroplating, pigment production, for soldering, brazing alloys, alarm systems, automatic sprinklers and nuclear shielding. It has been restricted by RoHS to 100ppm.

4) Hexavalent chromium (Cr6+) - It is used in photography, paints, plastics and stainless steel products. It is restricted by RoHS to 1000ppm.

5) Polybrominated biphenyls (PBB) – It is used in flame- retardants, plastic foams, and certain plastics used in home electrical appliances. It is restricted by RoHS to 1000ppm.

6) Polybrominated diphenyl ether (PBDE) - They are used in household electronics, printed circuit boards and capacitors. It is restricted to 1000ppm.

7) Bis(2-ethylhexyl) phthalate (DEHP)

8) Butyl benzyl phthalate (BBP)

9) Dibutyl phthalate (DBP)

10) Diisobutyl phthalate (DIBP)

DEHP, BBP, DBP and DIBP were additional added as part of DIRECTIVE (EU) 2015/863 which was issued on 31 March 2015.

RoHS Certification or RoHS Implementation

  • The purpose of the RoHS regulations is to decrease the intensities of the hazardous substances within electronic equipment or component. 
  • It may be essential to carry out RoHS testing to confirm that products are free of the substances banned under the RoHS regulations.
  • With the throw or dumping of electronic instruments or components, it has been found the levels of hazardous substances in the environment have been increasing.
  • One of the main areas of the RoHS has been to decrease the level of lead. However as seen above there are many more substances other than lead also involved in the legislation.
  • In order to limit or control the levels of substances maximum acceptable levels are fixed for the substances.
  • Maximum concentrations of 0.1% by weight of similar material are set for all except Cadmium, which is more poisonous; the maximum level is set to 0.01%.
  • These limits do not applicable to a whole product; it is applicable to any element, component or substance that could be separated from it.
  • In an example this could apply to the solder used in a printed circuit board. It could similarly apply to the plastic insulation of a wire. In this way, the whole thing that is used in the manufacturing of a product must be RoHS compliant.
  • Manufacturers of electronic equipment have been to implement soldering processes that are lead free to deliver RoHS compliance.
  • It also sets limits of 5 ppm mercury and 20 ppm cadmium to batteries excluding those used in medical, emergency, or handy power-tool devices.
  • Producers of electronics and electrical equipment’s or components within the scope of the RoHS directive are liable for confirming that their products meet the requirements of the RoHS directive.
  • Moreover, the act of employing a product in the market is an affirmation by the producer that the product complies with the RoHS directive.
  • It is essential that producers can prove the compliance of any product that they place in the market by obtaining and maintaining necessary technical documentation.
  • The RoHS necessities relate to the end products that fall within the scope of the RoHS directive.
  • The components and sub-assemblies used within the end products are not precisely covered by the scope of the RoHS directive and so no need to comply with the directive.
  • Though, as a final product is made up of components and sub-assemblies it is expected that all components and group of components forming sub-assemblies in the final product must not contain any of the restricted substances above the defined maximum concentration limits.
  • To validate compliance, a manufacturer must show that all the components, materials, sub-assemblies that involved in the product are RoHS compliant.
  • To avoid costly testing of all components, the easiest way to do this is to get certification from that supplier.
  • Manufacturers are also estimated to execute certain compulsory analysis of components. Technical documents must be present as a part of the CE Marking procedure.

RoHS application

The RoHS directive relates to a extensive range of products. The scope of the directive relates to equipment that is defined in the WEEE directive. These include:
  • Large and small household applications or appliances
  • IT related equipments
  • Telecommunication related equipment
  • Equipment for consumer applications
  • Lighting equipment
  • Electronic and electrical tools
  • Toys and sports equipment
  • Semiconductor devices
  • Automatic vending machines
One of the main exceptions from the RoHS directive is the batteries, which are not involved in RoHS, in spite of the high levels of substances that would usually come under RoHS.

The RoHS Directive does not apply to the glass used in cathode ray tubes and fluorescent tubes. Mercury-vapor light bulbs are also not considered in RoHS.

Conclusion

The RoHS directive is intended for eliminating certain hazardous substances from electrical and electronic equipment’s or components. Producers of these equipment’s or components within the scope of the directive are liable for confirming that their products meet the necessities of the RoHS directive. The RoHS necessities apply to the final products that fall within the range of the RoHS directive. Though, as an end product is made up of many components and sub-assemblies it is expected that all components and sub-assemblies must not cover any of the prohibited substances above the defined maximum concentration limits.

Friday, December 21, 2018

Magnetic properties of the material


We know the meaning of Hysteresis loop or B-H curve. Let discuss in detail the Magnetic properties of the material or in other word we can say that let discuss basic parameters of Hysteresis loop.
Please visit my previous blog to know more about;

Below picture shows, B-H curve (Hysteresis loop) in detail.
Hysteresis loop
B-H curve
Below are the magnetic properties of the material;

Permeability

When a magnetic field is applied to a soft magnetic material, the resulting flux density is composed of that of free space plus the contribution of the aligned domains.

B = μ₀H + J or B = μ₀ (H + M)
Where; μ₀ = 4πx10¯⁷H/m,
J is the magnetic polarization
M is the magnetization.

Absolute permeability

The ratio of flux density and applied field is called absolute permeability.
μabsolute = B/H = μ₀ [1+(M/H)]

It is usual to express this absolute permeability as the product of the magnetic constant of free space and the relative permeability (μᵣ).
B/H = µ₀ µᵣ

There are several versions of μᵣ depending on conditions the index ‘r’ is generally removed and replaced by the applicable symbol e.g. μᵢ, μₐ, μΔ etc.

Relative permeability

Relative permeability shows that how the presence of a particular material affects the relationship between flux density and magnetic field strength. The term 'relative' arises because this permeability is defined in relation to the permeability of a vacuum.

Initial permeability

Initial permeability describes the relative permeability of a material at low values of Magnetic Flux Density (below 0.1T). Low flux has the advantage that every ferrite can be measured at that density without risk of saturation. It is helpful for the comparison between different ferrites.
μᵢ = [(1/µ₀) x (ΔB/ΔH)] (ΔH → 0)
Initial permeability is dependent on temperature and frequency.

Effective permeability

If the air-gap is introduced in a closed magnetic circuit, magnetic polarization becomes more difficult. As a result, the flux density for a given magnetic field strength is lower.
Effective permeability is dependent on the initial permeability of the soft magnetic material and the dimensions of air-gap and circuit.

µₑ = µᵢ / {1+ [(G x µᵢ)/lₑ]}
Where;
G is the gap length and le is the effective length of magnetic circuit. This simple formula is a good approximation only for small air-gaps. For longer air-gaps some flux will cross the gap outside its normal area (stray flux) causing an increase of the effective permeability.
Comparison of hysteresis loops for a ferrite core with and without an air gap
Comparison of hysteresis loops for a ferrite core with and without an air gap

Apparent permeability

The definition of µₐᵨᵨ is particularly important for specification of the permeability for coils with tubular, cylindrical and threaded cores, since an unambiguous relationship between initial permeability µᵢ and effective permeability μₑ is not possible on account of the high leakage inductances. The design of the winding and the spatial correlation between coil and core has a considerable influence on µₐᵨᵨ. A precise specification of µₐᵨᵨ requires a precise specification of the measuring coil arrangement.
µₐᵨᵨ= L / L₀ = Inductance with core/ Inductance without core

Amplitude permeability

It is the relationship between higher magnetic field strength and flux densities; it is the permeability at high induction level. At relatively low induction, it increases with H but as the magnetization reaches saturation, it decreases with H. Helpful to find high permeability level of a material.
µₐ = (1/µ₀) x (^B/Ĥ)
Since the BH loop is far from linear, values depend on the applied field peak strength.

Incremental permeability

The permeability observed when an alternating magnetic field is superimposed on a static bias field, is called the incremental permeability.
μΔ = (1/µ₀)[ΔB/ΔH]Hᴅᴄ
If the amplitude of the alternating field is negligibly small, the permeability is then called the reversible permeability (μᵣₑᵥ).

Complex permeability

To enable a better comparison of ferrite materials and their frequency characteristics at very low field strengths (in order to take into consideration the phase displacement between voltage and current), it is useful to introduce μ as a complex operator, i.e. a complex permeability  ͞µ, according to the following relationship:
͞µ = μs' – j . μs"
Where, in terms of a series equivalent circuit, (see figure 5)
μs' is the relative real (inductance) component of ͞μ and μs" is the relative imaginary (loss) component of ͞μ.
Using the complex permeability ͞μ, the (complex) impedance of the coil can be calculated:
͞Z = j ω  ͞μ L₀
Where L₀ represents the inductance of a core of permeability μr = 1, but with unchanged flux distribution.
Complex Permeability vs Frequency
Complex Permeability vs Frequency
Figure at above shows the characteristic shape of the curves of μ' and μ" as functions of the frequency, using a NiZn material as an example. The real component μ' is constant at low frequencies, attains a maximum at higher frequencies and then drops in approximately inverse proportion to f. At the same time, μ" rises steeply from a very small value at low frequencies to attain a distinct maximum and, past this, also drops as the frequency is further increased.
The region in which μ' decreases sharply and where the μ" maximum occurs is termed the cut-off frequency fcutoff. This is inversely proportional to the initial permeability of the material (Snoek’s law).

Reversible Permeability


In order to measure the reversible permeability μᵣₑᵥ, a small measuring alternating field is superimposed on a DC field. In this case μᵣₑᵥ is heavily dependent on Hᴅᴄ, the core geometry and the temperature.

Power loss

It should be considered for high frequency/excitation application. It is the addition of Hysteresis losses, Eddy current losses and Residual losses. It should be <1.

PL = Physteresis + Peddy current + Presidual

Saturation flux density

It is how much magnetic flux the magnetic core can handle before becoming saturated and not able to hold any more. It should be high. Use minimum number of turns in winding.

Remanence

The magnetic flux density remaining in a material, especially a ferromagnetic material, after removal of the magnetizing field. It measures the strongest magnetic field ferrite can produce. There should be low retentive. So, ferrite should not magnetize easily without the application of magnetic field.

Coercivity

It is the magnetizing field strength required to bring the magnetic flux density of a magnetized material to zero. It should be low, so that it requires low magnetic field thus low opposite current to bring it back to the non-magnetic state.

Hysteresis Material constant

It is useful for estimating ferrite core losses. It is a constant that represents hysteresis loss when a magnetic material is operating in the Rayleigh region (low magnetic field region - behaviour of magnetic materials at low field). It should be less.
Hysteresis Constant is given by: ηв = (Δ tanδm) / [μe × Δ(^B)]

Disaccommodation Factor

Disaccommodation occurs in ferrites and is the reduction of permeability with time after a core is demagnetized. This demagnetization can be caused by heating above the Curie point by applying an alternating current of diminishing amplitude or by mechanically shocking the core. The value of dis-accommodation per unit permeability is called disaccommodation factor. It is a gradual decrease in permeability. It should be low and should be <2.
DF = (µ₁ -µ₂)/ [log₁₀ (t₂/t₁)] (1/µ₁²) (t₂>t₁)
Where;
µ₁ = resulting complete demagnetization, the magnetic permeability after the passing of t₁ seconds.
µ₂ = resulting complete demagnetization, the magnetic permeability after the passing of t₂ seconds.

Curie temperature

The transition temperature above which a ferrite loses its ferromagnetic properties. It should be high.

Resistivity

High resistivity makes eddy current losses extremely low at high frequencies. Resistivity depends on temperature and measuring frequency. Ferrite has DC resistivity in the crystallites of the order of 10⁻³Ωm for a MnZn type ferrite, and approx. 30 Ωm for a NiZn ferrite.

Relative loss factor

With the frequency increase, core loss is generated by the changing magnetic flux field within a material.
Core-loss factor, is defined as the ratio of core-loss resistance to reactance, and consists of three components; namely, hysteresis loss, eddy-current loss and residual loss.
Addition of an air gap to a magnetic circuit changes the values of its loss factor and effective permeability. The amounts of change are nearly proportional to each other.
It should be less.
This factor is defined as the loss angle tangent divided by permeability, Relative loss factor = tanδ/μᵢ
The loss angle tangent, tanδ, is decreased by an air gap in proportion to the ratio of permeability’s before and after air gap presence.

tanδₑ = (tanδ/µᵢ) µₑ

Where;
tanδ and μᵢ : permeability and loss angle tangent without an air-gap μₑ.
tanδₑ: permeability and loss angle tangent with an air-gap.
Hence, the relative loss factor, tanδ/μᵢ does not depend on air gap size, when the air-gap is small.

Quality Factor

It is the reciprocal of loss angle tangent.

Q = ωL/R˪ = 1/tanδ = reactance / resistance

Temperature factor of permeability
Temperature coefficient is defined as the change of initial permeability per °C over a prescribed temperature range. Temperature factor of permeability is defined as the value of temperature coefficient, per unit permeability. The measured value should be less.

It is the ratio of “Temperature factor for initial magnetic permeability” to the “initial magnetic permeability“.
αµ = αµ₁/µ₁ = [(µ₂-µ₁)/µ₁] [1/(T₂-T₁)] (T₂>T₁)
αµγ = [(µ₂-µ₁)/µ₁²] [1/(T₂-T₁)] (T₂>T₁)
where,
µ₁ = initial magnetic permeability at temperature T₁
µ₂ = initial magnetic permeability at temperature T₂

Density

It is calculated by;
d = W / V  (g/cm³)

Where;
W = Magnetic core weight
V= Magnetic core volume

Conclusion

Magnetic properties of material help us to select perfect material according to application. Even in the case of failure of application we can analysis the material properties and cause of failure easily we can find. Also, it helps us to find maximum working limit of a material.

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