Q factor

 
Q factor

Q Factor definition The Q factor of a capacitor, also known as the quality factor, or simply Q, represents the efficiency of a given capacitor in terms of energy losses. It is defined as: where QC is the quality factor, XC is the reactance of the capacitor, C the capacitance of the capacitor, RC is the equivalent series resistance (ESR) of the capacitor, and ω0 is the frequency in radians at which the measurement is taken. In an AC system, the Q factor represents the ratio of energy stored in the capacitor to the energy dissipated as thermal losses in the equivalent series resistance. For example, a capacitor that is capable of storing 2000 joules of energy while wasting only 1 joule has a Q factor of 2000. Since Q is the measure of efficiency, an ideal capacitor would have an infinite value of Q meaning that no energy is lost at all in the process of storing energy. This is derived from the fact that the ESR of an ideal capacitor equals zero. The Q factor is not a constant value. It changes significantly with frequency for two reasons. The first reason is the obvious ω0 term in the above equation. The second reason is that ESR is not a constant value with regard to frequency. The ESR varies with frequency due to the skin effect, as well as other effects related to the dielectric characteristics. A related term, called the dissipation factor(DF), is sometimes defined in capacitor datasheets instead of the Q-factor. In AC circuits the DF is simply the reciprocal value of Q. Why is the Q factor important? Most applications do not have to take the Q factor into serious consideration, and standard capacitors may be used in those applications. However, the Q factor is one [… read more]

Dielectric Materials

 
Dielectric Materials

Dielectric materials Dielectric materials are essentially insulators, which means that no current will flow through the material when a voltage is applied. However, certain changes do happen at the atomic scale. When a voltage is applied across a dielectric object, it becomes polarized. Since atoms are made of a positively charged nucleus and negatively charged electrons, polarization is an effect which slightly shifts electrons towards the positive voltage. They do not travel far enough to create a current flow through the material – the shift is microscopic, but has a very important effect, especially when dealing with capacitors. Once the voltage source is removed from the material, it either returns to its original non-polarized state, or stays polarized if the molecular bonds in the material are weak. The difference between the terms dielectric and insulator is not very well defined. All dielectric materials are insulators, but a good dielectric is one which is easily polarized. The amount of polarization which occurs when a certain voltage is applied to an object influences the amount of electrical energy that is stored in the electric field. This is described by the dielectric constant of the material. The dielectric constant is not the only property of dielectric materials. Other properties such as dielectric strength and dielectric loss are equally important in the choice of materials for a capacitor in a given application. Dielectric constant The dielectric constant of a material, also called the permittivity of a material, represents the ability of a material to concentrate electrostatic lines of flux. In more practical terms, it represents the ability of a material to store electrical energy in the presence of an electric field. All materials, including vacuum, store energy when placed in an electric field. The permittivity of vacuum is defined as the physical constant ε0, [… read more]

Impedance and Reactance

 
Impedance and Reactance

Impedance and reactance An element in a DC circuit can be described using only its resistance. The resistance of a capacitor in a DC circuit is regarded as an open connection (infinite resistance), while the resistance of an inductor in a DC circuit is regarded as a short connection (zero resistance). In other words, using capacitors or inductors in an ideal DC circuit would be a waste of components. Yet, they are still used in real circuits and the reason is that they never operate with ideally constant voltages and currents. As opposed to constant voltage circuits, in AC circuits the impedance of an element is a measure of how much the element opposes current flow when an AC voltage is applied across it. It is basically a voltage to current ratio, expressed in the frequency domain. Impedance is a complex number, which consists of a real and an imaginary part: where Z is the complex impedance. The real part R represents resistance, while the imaginary part X represents reactance. Resistance is always positive, while reactance can be either positive or negative. Resistance in a circuit dissipates power as heat, while reactance stores energy in the form of an electric or magnetic field. Impedance of a resistor Resistors in AC circuits behave the same way they do in DC circuits. Basically, the impedance of a resistor consists only of the real part, which is equal to the resistance of the resistor. Therefore, the impedance of a resistor can be expressed as: where Z is the impedance, and R is the resistance of the resistor. It is obvious that a resistor has no reactance, and can therefore store no energy. Also, when a voltage is applied across the resistor, the current flowing through the resistor will be in phase with the voltage, [… read more]

Parasitic Inductance

 
Parasitic Inductance

What is inductance? Electric inductance is a property of all conductors. A change in the current flowing through the conductor creates (induces) a voltage in that conductor, as well as all nearby conductors. The induced voltage opposes the change in the current that induced the voltage. Inductance is a consequence of two laws of physics. Firstly, a constant current flowing through a conductor creates a constant magnetic field. Secondly, a variable magnetic field induces a voltage in all nearby conductors, including the conductor which was used to create the magnetic field in the first place. When these two laws are combined, the resulting effect is inductance. Just like resistors are used to introduce a desired resistance in a circuit, and like capacitors are used to introduce a desired capacitance, inductors are electrical elements used to introduce a desired amount of inductance into the circuit. The inductance formula for an ideal solenoid (a coil of wire) wound around a cylindrical body of material is given as:     where L is the inductance, µ is the magnetic permeability of the material used in the inductor, A is the cross-sectional area of the coil and l is the length of the solenoid (not the length of the wire, but the longitudinal dimension of the coil). An ideal capacitor has no resistance and no inductance, but has a defined and constant value of capacitance. The unit used to represent inductance is henry, named after Joseph Henry, an American scientist who discovered inductance. Parasitic inductance Parasitic inductance is an unwanted inductance effect that is unavoidably present in all real electronic devices. As opposed to deliberate inductance, which is introduced into the circuit by the use of an inductor, parasitic inductance is almost always an undesired effect. There are few applications in which parasitic inductance is [… read more]

Capacitance

 
Capacitance

What is capacitance? Electric capacitance is the ability of a conducting body to accumulate charge. The capacitance value of a capacitor is obtained by using the formula: where C is the capacitance, Q is the amount of charge stored on each electrode, and V is the voltage between the two electrodes. In real life circuits the amount of charge on one plate equals the amount of charge on the other plate of a capacitor, but these two charges are of different signs. By examining this formula it can be deduced that a 1 F capacitor holds 1 C of charge when a voltage of 1V is applied across its two terminals. The unit of capacitance The unit of capacitance is a Farad [F]. This unit can be somewhat impractical. From the vantage point of most electrical engineers, one farad is a huge capacitance value. Most electronic circuits use capacitors of only up to a few mF. There are several good reasons for this. One reason is that, when dealing with signals in an electrical circuit, as the frequency of the signal increases, the need for high capacitance capacitors decreases because, at higher frequencies, even a small capacitor can make a big impact on the circuit. Since most modern digital circuitry has a tendency to move towards higher frequencies in order to meet demands for improved processing speed, these circuits mostly use capacitors of only up to a few mF. As a result, the need for large capacitors is virtually non-existent in the signals processing parts of electrical circuits. Another reason is that high capacitance capacitors are physically large. Therefore, the use of such capacitors is avoided, especially in mobile devices. However, there have been recent technology advances in the field of supercapacitors. Thanks to these advances, it is now possible [… read more]

Electric Charge

 
Electric Charge

What is electric charge? Electric charge is a fundamental physical property of matter. Electric charge can be positive or negative. Matter repels other matter of the same charge and attracts other matter having the opposite charge. The unit used for electric charge is a Coulomb [C]. While the exact nature of charge is still unknown at a fundamental level, it is generally accepted to represent a specific state of matter which cannot be explained at the current level of scientific knowledge. Electric charge is quantized, meaning that charge can only have discrete values. An elementary charge is denoted as e, and approximately equals 1.602·10-19 C. The electron bears a charge of -e and it is a negatively charged particle. In contrast, a proton is a positively charged particle, bearing a charge of +e. An intuitive way to understand the quantized nature of charge is to imagine an electrically neutral object as a box containing an equal number of protons (positive charges) and electrons (negative charges). Protons are fixed and cannot be taken out or added to the box. Since the number of protons and electrons is equal, the total sum of the electric charge inside the box is zero for electrically neutral objects. In order to make the object negatively charged, the only way to do so is to somehow add more electrons into the box. As electrons are indivisible particles, it is only possible to add an integer number of electrons – one cannot add half an electron into the box. As a result, the total charge of the object is N times the charge of a single electron, which equals -e·N, where N is an integer number. Similarly, in order to make an object positively charged, it is necessary to remove N electrons from the box and the [… read more]

Electric Field

 
Electric Field

What is an electric field? An electric field is a special state that exists in the space surrounding an electrically charged particle. This special state affects all charged particles placed in the electric field. The true nature of electric fields, as well as the true nature of an electric charge is still unknown to scientists, but the effects of an electric field can be measured and predicted using known equations.  Just like a magnet creates an invisible magnetic field around it, which can be detected by placing a second magnet in its field and measuring the attractive or repulsive force acting on the magnets, electric charges create an electric field which can be detected by using a test charge. When a test charge is placed inside an electric field, an attractive or repulsive force acts upon it. This force is called the Coulomb force. In fact, magnetic and electric fields are not entirely separate phenomena. A magnetic field that changes with time creates – or “induces” an electric field, while a moving electric field induces a magnetic field as a direct consequence of the movement. Because these two fields are so tightly connected, the magnetic and electric fields are combined into one, unified, electromagnetic field. Electric field definition The electric field can be defined as a vector field which describes the relationship between the charge of a test particle introduced in the field and the force exerted upon this charged test particle.  Where E is the electric field, F is the force exerted on the test particle introduced into the field and q is the charge of the test particle. The unit for electric field is volts per meter [V·m-1] or newtons per coulomb [N·C-1]. The application of electric field in capacitors Electromagnetism is a science which studies static and [… read more]

Ceramic Capacitor

 
Ceramic Capacitor

What are ceramic capacitors? A ceramic capacitor uses a ceramic material as the dielectric. Ceramics were one of the first materials to be used in the producion of capacitors, as it was a known insulator. Many geometries were used in ceramic capacitors, of which some, like ceramic tubular capacitors and barrier layer capacitors are obsolete today due to their size, parasitic effects or electrical characteristics. The types of ceramic capacitors most often used in modern electronics are the multi-layer ceramic capacitor, otherwise named ceramic multi-layer chip capacitor (MLCC) and the ceramic disc capacitor. MLCCs are the most produced capacitors with a quantity of approximately 1000 billion devices per year. They are made in SMD (surface-mounted) technology and are widely used due to their small size. Ceramic capacitors are usually made with very small capacitance values, typically between 1nF and 1µF, although values up to 100µF are possible. Ceramic capacitors are also very small in size and have a low maximum rated voltage. They are not polarized, which means that they may be safely connected to an AC source. Ceramic capacitors have a great frequency response due to low parasitic effects such as resistance or inductance. Ceramic capacitor definition A ceramic capacitor is a capacitor which uses a ceramic material as the dielectric. The two most common types are multi-layer ceramic capacitors and ceramic disc capacitors. Characteristics Precision and tolerances There are two classes of ceramic capacitors available today: class 1 and class 2. Class 1 ceramic capacitors are used where high stability and low losses are required. They are very accurate and the capacitance value is stable in regard to applied voltage, temperature and frequency. The NP0 series of capacitors has a capacitance thermal stability of  ±0.54% within the total temperature range of -55 to +125 °C. Tolerances of the nominal capacitance [… read more]