High Performance Capacitor are discusse to very complex level. If you need some other high voltage articles visit here.
Basic Considerations of High Performance Capacitor
The dissipation factor (DF), the quality factor (Q) and the equivalent series resistance (ESR) are important parameters of high-performance capacitors. Their role in low impedance or high current circuits, such as power supplies, amplifiers and high current filters, is particularly significant. DF, Q and ESR represent heat generation losses within the condenser. Minimizing these losses and thereby reducing the heat promotes greater stability, less distortion and a shorter mean time before failure (MTBF).
Dissipation factor (DF)
DF and “loss tangent” are largely equivalent terms that describe the dielectric losses of the capacitor. DF specifically refers to losses at low frequencies, typically 120 Hz to 1 kHz. At high frequencies, the losses of dielectric capacitors are describe as loss tangents (tan δ). The higher the loss factor, the greater the equivalent series resistance (ESR) of the capacitor to the signal power. The worse the quality factor (low Q), the greater the loss (heating) and the worse the noise properties.
When a capacitor is use as a series element in a signal path, its direct transfer coefficient is measure as a function of the dielectric phase angle (θ). This angle is the phase difference between the applied sine voltage and its current component. In an ideal condenser (θ) it is 900. In low loss capacitors it is very close to 90 °.
At small and moderate capacitor values, losses within the capacitor occur primarily in the dielectric, the medium for energy transmission and storage. The dielectric loss angle is δ the difference between (θ) and 90 ° and is generally know as tan or. The name “loss tangent” simply indicates how tan δ goes to zero when losses go to zero. It should be noted that the DF of the dielectric is also the tangent of the dielectric loss angle. These terms are use synonymously in the literature.
Quality Score (Q)
The quality factor (Q) is the ratio between the stored energy and the energy consumed per cycle. This is define for a reactive component:
Q = Xc / Resr = tan (θ) In one aspect, Q is a figure of merit because it defines a circuit component’s ability to store energy compare to the energy it wastes. The rate of heat conversion is generally proportional to the power and frequency of the energy applied. However, the energy entering the dielectric is damped at a rate that is proportional to the frequency of the electric field and the dissipation factor of the material. If a capacitor stores 1000 joules of energy and dissipates only 2 joules, it has a Q of 500. The energy stored in a capacitor (joules. Watt-sec.) = 1/2 C (V2).
Equivalent series resistance (ESR)
The equivalent series resistance (ESR) is responsible for the energy emitt as heat and is directly proportional to the DF. A capacitor should be represents as an ESR in series with an ideal capacitance (C). ISR is determined by:
ESR = (Xc / Q = Xc (tan δ), with Q = 1 / DF.
From this we can see that “lossy” capacitors and those with large amounts of Xc are very resistant to signal performance.
Circuit designs using low Q capacitors generally generate large amounts of undesirable heat because tan δ and DF (or 1 / Q) generally increase non-linearly with increasing frequency and temperature. With some capacitors, this effect is exacerbated by the reduced capacitance that occurs naturally at high frequencies. High currents also generate increased heat, which in turn increases ESR and DF.
Even with significant changes in current flow, high Q (low DF) capacitors do not have the value changes that are common to high DF, ESR, and other parasitic properties. A low ESR reduces the unwanted heating effects that affect capacitors. This is an important goal when designing these components for high current, high performance applications such as power supplies and high current filter networks.
Physical considerations of high Performance Capacitor
- Other factors contribute to additional losses
- bulk material from cables
- Lead fixation methods
- Capacitor plate material
- general construction.
Especially with larger capacity values, these factors make up a significant percentage of the total loss as your contribution to the ESR increases.
There are three types of losses in a film capacitor: metal losses (Rs); Leakage or loss of insulation at DC or low frequencies (Rin); and dielectric losses (Rda). Apart from the long shunt, the following formula shows how these three losses are related to the ESR of a capacitor:
ESR = Rs + 1 / Rin (2 (pi) fC) 2 + DF / 2 (pi) fC
Metal losses include all losses in the capacitor cables, termination connections and capacitor plates. As shown in the equation above, losses due to insulation resistance leak (Rin) (second term) predominate, especially at low frequencies. With increasing frequency, the dielectric losses (third term) and then the metal losses (first term) come to the fore.
More Physical considerations of high Performance Capacitor
Metallized film capacitors with thin conductors or plates have a significant size advantage over other types: they can be very small. These capacitors are form by a vacuum deposition process that laminates a film substrate with a thin aluminum coating measured in angstroms. They are use when small signal levels (low currents / high impedances) and small physical size are the main factors. They are generally unsuitable for large signal AC applications.
The film and foil capacitor has much thicker plates than the foil; These plates result in less loss. The thicker sheet also helps remove heat build-up. This means longer life, higher reliability and minimal impact on the dielectric or DF of the capacitor. Film and foil construction capacitors can be used in small and large signal applications, but higher performance (and higher price) may not be required in some small signal applications.
More Physical considerations of high Performance Capacitor
The resistance of the plate increases with its length, as does the value of the capacitor. A larger diameter plate can be used to compensate for a shorter length. This construction with short length and large diameter reduces the ESR due to the reduced resistance of the plate and increases the contact area between the plate and the line and prevents the increase in inductance that typically occurs in plate designs with a long length and small diameter.
The connection between the cables and the capacitor plate (s) also affects the ESR, generally for the worse. In addition to the size and shape of the cables (mentioned above), the following considerations are important: the fastening method (soldering or soldering); the size and shape of the capacitor; and the size of the sprayed metal droplet used to shorten all of the plates together. The long-term reliability and stability of ESR also depends on the use of metals that do not have an electrolysis effect, such as result from the direct contact of aluminum and copper.
At low capacitance values, the inherent loss factor of the dielectric material contributes significantly to the ESR. As the capacitance value increases, the resistance of the plate, the resistance of the line and the resistance of the final coating again become the dominant factors influencing the entire ESR. Careful selection and control of these factors leads to an evenly stable and low ESR.
Impedance, Inductance, and Resonant Frequency of High Performance Capacitor
The reactance of an ideal capacitor decreases with increasing frequency, as can be seen from the formula: Xc = 1 / (2 (pi) f C). Of course, due to the ESR and the inductance (L) of the capacitor, the impedance (Z) also changes with frequency, as shown in figure 5.
The minimum impedance point (ESR) marks the frequency at which L and C form a series resonance circuit, the inductive reactance being equal to the capacitive reactance. Above this resonance frequency, the capacitor acts as an inductor. For many applications, the series resonant frequency of the capacitor is the useful upper frequency limit of a circuit, especially when the phase angle of the capacitor is expected to maintain a voltage-to-current ratio of 90 degrees (tan θ = 0) or almost 90 degrees. This is a common assumption when designing filter networks.
The length of the capacitor and its structure determine the capacitor’s self-inductance and, therefore, its resonance frequency. The length of the cable when the capacitor’s external circuit is loaded affects the circuit’s performance in a very different way than that calculated under the ideal conditions (i.e. without inductance). Figure 6 shows the effect of increasing the cable length from 3/8 ‘/ to 3 “, a typical length
when the trace length of the circuit board or circuit wiring is added to the length of the capacitor cable. Note that the useful upper frequency limit is from 490 kHz to about 290 kHz. The reduction for this special capacitor is about 33 kHz per inch! For a dielectric loss angle of 10 degrees (tan θ =. 176) in the audio pass-band (often with larger capacitor, inductance and ESR values) there is an even stronger effect: the corresponding frequencies for 1/4 “and 3” cable lengths are 260 kHz and 141 kHz
The MultiCap Capacitors
Multi Cap reduces typical capacitor loss factors through a new. Patented design in which capacitors are co axially wound on top of each other in one unit. Since each section of the coaxial capacitor is parallel, the inductance of the . General capacitor is reduce by the number of sections use. In fact the inductance properties never exceed that of a piece of wire that is the same length as the body of the capacitor!
Although there is no theoretical limit to the number of sections. Practical manufacturing considerations make a ten-section construction the optimal choice. The measured ESR values are 5 to 10 times lower than with conventional designs and are sometimes only close to a few hundred micro ohms (11 uf), with typical values well below 0.001 ohms. This remarkable performance is due in part to the fact that Multi Cap uses a plate length to diameter ratio as close as possible to 1: 1 across the full range of values.
In addition to its unique configuration, MultiCap uses the best materials. Its film materials have the lowest dielectric absorption among the capacitors used today. By using fine materials, DF and ESR are reduced to extremely low values for maximum signal resolution.
Advantages Disadvantages Contd
The MultiCap DF is typically 0.00003 to 0.0003 compared to some equivalent conventional values of 0.12 or more. MultiCap has significant advantages, especially in high current applications where losses can be significant. Solving the equation: Power loss (watts) = 2 (pi) c (V2) (DF) for a 200 uf / 50V capacitor with a typical DF of 0.12 at 120 Hz shows a heat loss of more than, for example. 37 watts! An equivalent MultiCap would generate less than 44 microwatts of unwanted heat under identical operating conditions.
The MultiCap also solves the multiple resonance problems that occur when reducing the high frequency impedance of a circuit by externally parallelizing. A conventionally large wound capacitor with smaller ones. This is a trial-and-error design process that leads to a complex combination of parallel and series resonances. These can be minimize and frequently eliminated through the multi-part coaxial design of MultiCap.
Advantages Disadvantages Contd
Without careful Xc and phase-to-frequency measurements of a particular capacitor, you’re not sure what type of capacitor, what brand, and what value should be connected in parallel. 8 shows the out-of-circuit impedance of one brand of a 25 HF electrolytic capacitor in parallel with smaller values of different brands. Note that larger values for film capacitors have a greater impact on impedance.
The same capacitor is show, which shows that excessive line lengths not only reduce the resonant frequency of parallel capacitors, but can also completely cancel out the effects of the added parallel capacitor.
Another aspect of parallelization is show, in which the resonant frequency of the circuit causes an applied signal to sound. Lower resonance frequencies in the circuit increase the chance that signal components will modulate with the resonance artifact. A MultiCap that offers the performance of small parallel values in a single unit can save valuable development time by reducing the parallelization of attempts and errors. In some cases, the MultiCap also saves space.
The Multi Cap in Quality factor and loss factor
A quick check of the formulas for Q, DF and natural resonance frequency shows how easily a high-performance capacitor can deteriorate. Very short termination paths are require at each connection in order to avoid deterioration: only a few milli-ohms ESR or nano-Henry inductance reduce a Q of thousands to hundreds of ohms.
Replacing conventional capacitors of different brands in existing circuits is also problematic, especially if these circuits are specifically design for a particular brand that does not have ideal properties. Peculiarities of another brand can lead to undesirable results. See Figure 11. For best performance, a circuit should be design with the most ideal components available. These components enable more stable signal processing with finer resolution and level of detail.
Of course, circuitry and wiring methods can also generate stray parasites that dominate the stray contributions of a high-power capacitor.For example. The actual performance of an equalizer model or filter circuit sometimes does not meet expectations. This generally occurs because the model has not considered the effects of the component parasitic elements. the parasitic parasites that result from the design and wiring of the circuit. Here too, optimizing the entire design with the most ideal capacitor leads to the best results.
Capacitors in real applications – High Performance Capacitor
The capacitor is one of the main basic components of electronic circuits. The basic structure consists of a dielectric material which is arranged between two electrodes or plates.
The impedance of an ideal capacitor is give as Z = Xc = 1/2 (pi) fC. If it is shown graphically, would lead to a straight line that comes closer to zero with increasing frequency (f).
However, no component of the circuit is ideal, i.e. purely restive or purely reactive. All components of the circuit have a combination of complex impedance elements. inductors show undesirable capacitance and hysteresis effects. The resistors show undesirable inductance properties. Capacitors have undesirable inductance, resistance and dielectric absorption. Different materials and manufacturing techniques produce different amounts of these unwanted parasites that affect a component’s performance. All components, including those made with the best materials and processes. Have some of these artifacts and must therefore be model as complex impedances. (See Figures 1 A and 1 B.)
More Capacitors in real applications – High Performance Capacitor
In addition to capacitance (C). Two other parameters, loss factor (DF) and equivalent series resistance (ESR), are generally measured to reflect the presence of parasites.
This document defines various capacitor-based parasites and examines their relationships and effects on the performance of a capacitor. Dielectric absorption is not discussed in detail here: anyone wanting technical details should refer to Richard Marsh’s previous pioneering work. In short, dielectric absorption has emerged as the main cause of distortion in audio circuits. Dielectric film type capacitors, particularly polystyrene, have very low dielectric absorption and are therefore preferred in audio circuits.
References for High Performance Capacitor
“Dielectric Absorption,” Marsh, The Audio Amateur, April 1980
“Capacitors,” Walt Jung & Richard Marsh, Audio Magazine, Feb)/March 1980
High Performance Capacitor are discussed to very complex level. If you need some other high voltage articles visit here.