File Name: difference between ceramic and electrolytic capacitor .zip
There are numerous types of capacitors with various functions and applications. Capacitors range from small to large, and each has characteristics that make them unique. For example, some capacitors are small and delicate, such as the ones found in radio circuits. On the other hand, capacitors can be quite large such as those found in smoothing circuits.
Multiple capacitors are used in electronic devices. Aluminum and tantalum electrolytic capacitors are used in applications which require large capacitance, but miniaturizing and reducing the profile of these products is difficult and they possess significant problems with self-heating due to ripple currents.
However, due to the advances in large capacitance of MLCCs in recent years, it has become possible to replace various types of capacitors used in power supply circuits with MLCCs. Switching to MLCCs provides various benefits such as a small size due to the miniature and low-profile form factor, ripple control, improved reliability and a long lifetime.
However, the low ESR equivalent series resistance feature of the MLCC can have adverse effects that may lead to anomalous oscillations and anti-resonance, so caution is required. Figure 1: The frequency band used by various capacitors and the range of capacitance.
Along with the increasing high integration of the primary LSI and IC components in electronic devices, there has been a trend toward low voltage in the power supplies which supply these components. In addition, power consumption has also increased with the progression of multi-functionality and the trend toward the use of high current continues. To support the trends toward low voltage and high current, the power supplies of electronic devices have switched from intermediate bus converters to adopt dispersed power supply systems which place multiple miniature DC-DC converters POL converters near the LSI and IC loads.
In a POL converter, multiple capacitors are externally attached. Previously, aluminum and tantalum capacitors were used in particular due to the need for large capacitance in output smoothing capacitors. However, the difficulty in miniaturizing these electrolytic capacitors is a hindrance to reducing the circuit space.
In addition, they possess significant problems with self-heating due to ripple currents. The MLCCs used in many electronic devices are capacitors with superior characteristics, but their capacitance is comparatively low and they have been used primarily in filter and high-frequency circuits. The primary features and cautions on usage of MLCC, aluminum electrolytic capacitors and tantalum electrolytic capacitors are indicated below. It is important to understand these cautions on usage as well as the merits and demerits of these capacitors when replacing them with an MLCC.
While large-capacitance MLCCs make it possible to replace electrolytic capacitors, it is important to note their shortcoming which is the large rate of change in capacitance due to temperature and DC bias. In addition, an ESR which is too low has adverse effects and may lead to anomalous oscillations in power supply circuits. Figure 2: Comparative example of capacitor's self-heating due to ripple currents frequency: kHz.
The capacitor's ESR changes according to the frequency. With the capacitor ESR at a certain frequency set as "R" and the ripple current set as "I", "RI 2 " becomes the power heat loss and the capacitor self-heats.
While large-capacitance is acquired using an electrolytic capacitor, significant heat develops due to ripple current and a high ESR , which is a weakness of electrolytic capacitors. The upper limit of the ripple current which the capacitor allows is called the "allowable ripple current". The life of the capacitor will decrease when the usage exceeds the allowable ripple current.
The ideal capacitor would possess only the properties of capacitance, but in reality it also contains resistor and inductor components due to the electrodes. The resistor component, not shown in the ideal capacitor, is called the "ESR equivalent series resistance " and the inductor component is called the "ESL equivalent series inductance ".
DC Direct Current is when current flows in one direction, but in dc power supplies in addition to DC current there are various superimposed alternating current components which adds ripple to the current. For example, the direct current resulting from the rectification full-wave rectification of commercial alternating current contains pulsating ripple currents at twice the cycle of the commercial alternating current.
In addition, the pulsating current of the switching cycle in a switching DC-DC converter is superimposed on the direct current voltage.
This is called the "ripple current". Aluminum electrolytic capacitors are widely used in electronic devices, because they have high capacitance and are inexpensive, but caution is required due to their limited lifetime.
The typical lifetime of an aluminum electrolytic capacitor is said to be ten years. This is because the capacitance decreases as the electrolytic solution dries up capacitance loss. The amount of electrolytic solution lost is related to temperature and closely follows the "Arrhenius equation" of chemical reaction kinetics.
For this reason, the lifetime is reduced even more when used under conditions with significant self-heating due to ripple currents. The drying up of the electrolytic solution also increases the ESR. Attention should be noted that the peak value of the ripple voltage does not exceed the rated voltage withstanding voltage when the ripple voltage is superimposed on the direct current voltage.
A capacitor used in a power supply circuit has a rated voltage that is three times of the input voltage. Capacitor heat generation due to ESR and ripple currents is a predominant issue in the output capacitors of power supply circuits. Figure 7 shows the fundamental circuit of a miniature step-down DC-DC converter which is used as a POL converter in many electronic devices.
This type of output capacitor is the primary target for replacement of electrolytic capacitors with MLCCs in DC-DC converters as a solution for the self-heating issue, space reduction and improved reliability. Figure 8 shows the fundamental circuit of the miniature step-down DC-DC converter which is used as a POL converter in many electronic devices.
The main converter circuit has been made into an IC, and the capacitor and inductor are attached externally on the PCB internally attached products also exist. The capacitor which comes before the IC is called the "input capacitor Cin " and the one that comes after is the "output capacitor Cout ". In addition to collecting an electrical charge and smoothing the output voltage, the output capacitor in a DC-DC converter plays the role of grounding and removing the ripple component of the alternating current.
The output voltages of the step-down DC-DC converter's output capacitors were compared using the following type of evaluation board. The ripple voltage, which causes the self-heating, follows a similar pattern. The functional polymer aluminum electrolytic capacitor uses a conductive polymer as the electrolyte and is a type designed for a low ESR. Compared to the typical aluminum electrolytic capacitor, the ripple voltage is significantly smaller, but the form factor is slightly large and the price is expensive.
The impedance-frequency characteristics and ESR-frequency characteristics for each are as follows. Figure The impedance-frequency characteristics and ESR-frequency characteristics for various capacitors. As the capacitor ESR becomes lower, the ripple voltage can be kept to a smaller amount. For this reason, the MLCC displays optimal performance as a replacement for an electrolytic capacitor.
Replacing an electrolytic capacitor with an MLCC provides various advantages such as ripple control as well as space reduction of the circuit board due to the miniature and low-profile form factor, a long lifetime and an improvement in reliability.
Self-heating due to ripple currents in capacitors with a high ESR shortens the lifetime of the capacitor. The ESR of an electrolytic capacitor decreases slightly when the capacitance increases. However, it is fundamentally difficult to control the ripples by increasing the capacitance.
This is because the time constant increases together with the increase in capacitance. The response speed of a transient phenomenon such as the charging and discharging process of a capacitor can be expressed as the time constant index called T. The time required for charging and discharging of the capacitor is short when the time constant is small and becomes longer as the time constant increases.
The time constant becomes extremely large when using an electrolytic capacitor with an excessively large capacitance. In a DC-DC converter with repeated switching of a short duration, the discharging does not complete within the switch OFF time and charge remains in the electrolytic capacitor. As a result, the voltage does not sufficiently decrease, distortions occur in the voltage waveform, and the output becomes unstable, which does not allow for favorable ripple control Figure Figure Distortions occurring in the waveform of a large capacitance aluminum electrolytic capacitor.
MLCCs, on the other hand, do not have this kind of problem because of the low ESR over a wide frequency band, which achieves favorable ripple control in the place of an electrolytic capacitor. The low ESR is a feature of the MLCC, but it is so much lower compared to an aluminum electrolytic capacitor that on the contrary, the output voltage of the DC-DC converter becomes unstable and causes oscillations to occur. As shown in the figure on the right, the DC-DC converter compares the output voltage with the reference voltage, amplifies the error amount with the error amp error amplifier , and performs negative feedback to achieve a constant and stable direct current voltage.
However, signal phase lag occurs due to the inductor L and the capacitor C of the smoothing circuit. There is a board diagram used as a chart to determine whether the negative feedback will operate in a stable manner. The horizontal axis of the graph is the frequency and the vertical axis is the gain and phase.
Connect a capacitor and resistor near the error amp to reduce the phase lag and adjust to cancel it. This is called "phase compensation". Previous designs which used an aluminum electrolytic capacitor with a high ESR for the output capacitor did not have this problem. However, the MLCC has insufficient compensation, which causes anomalous oscillations, so caution is required when replacing capacitors.
Previously, electrolytic capacitors and MLCCs where connected in parallel for decoupling in an analog circuit, but with the productization of large-capacitance MLCCs, the replacement of electrolytic capacitors with MLCCs is advancing. In particular, large-capacitance is required to reduce impedance due to the large ESR in an aluminum electrolytic capacitor.
The miniaturization and low-profile of the MLCC also achieves a reduction in circuit board space, and the long lifetime and superior reliability are also replacement advantages. When a capacitor is connected in parallel to the power supply line of an IC, there is impedance in the power supply line, which is not shown in the circuit diagram, which can change the power supply voltage and cause a malfunction or interference between circuits.
A capacitor is connected in parallel to control the voltage variations through charging and discharging. Additionally, since a capacitor passes alternating current, it removes or directs ripple noise to ground. This is called a "decoupling capacitor" also called a "bypass capacitor". For decoupling use, the ideal capacitor would have low impedance across a wide band of frequencies from low to high, but in reality the impedance-frequency characteristics of a capacitor follow a V-shaped curve.
The frequency at the trough of the V-shape is called the "self-resonating frequency" SRF , and it functions as a capacitor in the region below the SRF. For this reason, capacitors with different characteristics are typically connected in parallel to cover a wide frequency band in decoupling applications. For example, multiple MLCCs are connected in parallel for decoupling in an IC operating with a large current and a low voltage.
The capacitor functions as a capacitor below the SRF self-resonating frequency frequency band and as an inductor above the SRF. This phenomenon is called "anti-resonance". Anti-resonance creates intense impedance peaks which weaken the noise removal effect at that frequency. This can cause the power supply voltage to become unstable and the circuit to malfunction. Please use it to improve the reliability of your products.
The MLCC is a superior capacitor, but it also has weaknesses. The capacitance of an MLCC changes according to the applied voltage. This is called the "DC bias characteristic" when a DC voltage is applied. This is caused by the intrinsic polarization of the ferroelectric BaTiO3, etc.
For this reason, please consider the dielectric characteristics, the voltage used and the withstanding voltage when making your selection if it is to be used when applying a DC voltage. There is also a tendency for the capacitance to be significantly reduced in miniature-sized capacitors.
The DC bias characteristics must also be considered when selecting the capacitance. Figure Rate of change in the capacitance - DC bias characteristic example high-dielectric constant. Figure Effects of the DC bias characteristic comparison of effective capacitance when 3.
An electrolytic capacitor is a polarized capacitor whose anode or positive plate is made of a metal that forms an insulating oxide layer through anodization. This oxide layer acts as the dielectric of the capacitor. A solid, liquid, or gel electrolyte covers the surface of this oxide layer, serving as the cathode or negative plate of the capacitor. Due to their very thin dielectric oxide layer and enlarged anode surface, electrolytic capacitors have a much higher capacitance - voltage CV product per unit volume than ceramic capacitors or film capacitors , and so can have large capacitance values. There are three families of electrolytic capacitor: aluminum electrolytic capacitors , tantalum electrolytic capacitors , and niobium electrolytic capacitors. The large capacitance of electrolytic capacitors makes them particularly suitable for passing or bypassing low-frequency signals, and for storing large amounts of energy.
the differences between the wide varieties of capacitors?" When your schematic calls for a capacitor, you have many choices: electrolytic, ceramic, silver mica.
Ceramic and electrolytic capacitors are two types of capacitors used in electronic circuits. A capacitor is a device that can store electrical energy. Basic structure of a capacitor. A ceramic capacitor is a type of capacitor whose dielectric is a ceramic material. In the simplest construction of these, a layer of a ceramic material sits between two conductive plates.
Tantalum capacitors configured with electrodes on the bottom of the package are not susceptible to shorts, even when mounted close together facing each other. This makes it possible to further decrease set thickness to a level that is difficult or impossible to achieve with ceramic capacitors. Resin-mold-type tantalum capacitors are typically strong against stress caused by board deflection.
Electrolytic vs Ceramic Capacitor. A capacitor is an electrical component which is able to store electrical charges. Capacitors are also known as condensers.
Capacitors are rated in microfarads designated by MFD or uF on the capacitor label. When replacing a capacitor, only replace it with the exact microfarad ratings as the original capacitor.
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