The decoupling capacitor…is it really necessary? Art Kay writes:
Before working as an applications engineer, I worked as an IC test development engineer here at TI. One of my projects was to characterize an I2C temperature sensor. After writing some software, I threw together a hand-wired prototype board. I was in a hurry, so I left off that pesky decoupling capacitor. Who needs it, right?
I collected data for about a week, and none of my results matched expectations. I made numerous changes in an attempt to improve performance, but nothing worked. Finally, I decided to add the decoupling capacitor. As you might expect, this solved the issue.
The decoupling capacitor…is it really necessary? - [Link]
mattthegamer463 @ instructables.com writes:
If you’ve ever been designing a circuit and had to experiment with different values of caps and resistors, you probably didn’t like it much. It can be a hassle to switch out components over and over, trying to find the right combination to suit your needs. With RC filter circuits, it can be quite difficult to determine what resistance and capacitance you need to get the filtering attributes you want. With a Selection box such as this just a turn of a knob can test many different values.
Build a Resistor/Capacitor Selection Box - [Link]
Dave proves he has no fear by opening this can of electronic worms by posing the question – “Does Current Flow Through A Capacitor?” The answer may surprise you, or drive you into a physics induced rage…
Does Current Flow Through A Capacitor - [Link]
Abstract: The reality of modern, small form-factor ceramic capacitors is a good reminder to always read the data sheet. This tutorial explains how ceramic capacitor type designations, such as X7R and Y5V, imply nothing about voltage coefficients. Engineers must check the data to know, really know, how a specific capacitor will perform under voltage. [by Mark Fortunato]
Temperature and Voltage Variation of Ceramic Capacitors, or Why Your 4.7µF Capacitor Becomes a 0.33µF Capacitor - [Link]
This project was conceived as a way to enhance the collection of test equipment on my test bench. I buy a lot of older HP test gear off ebay as well as older radios. Most of this gear is 25-60 years old and needless to say, the condition of the electrolytic capacitors is somewhat suspect. I needed a way to quickly weed out bad caps with an in circuit tester.
Analog Capacitor ESR Tester - [Link]
Thanks to their very low equivalent serial resistance (ESR), they provide a very worth function in power supply parts of various devices. In many cases, there´s no need to add any other types of filtering capacitors anymore.
SMD ceramic capacitors are nowadays commonly available in relatively very high capacities of units to tens of uF, while keeping small dimensions (0603 – 1210). There are also available higher capacities in bigger packages, but the offer of producers is especially reach at these small packages (0603-1210) and prices are significantly better in comparison to a recent past.
Why to use a ceramic capacitor? First, it has a substantially lower value of ESR than electrolytic capacitors and also lower than tantalum ones. This is reflected in low losses and outstanding filtering properties even at high frequencies and high currents, what is especially beneficial at power supply of fast semiconductors and in switch-mode power supplies. Low power consumption of modern components enables to decrease an overall capacity of capacitors in a power supply part, that´s why in many cases a few uFarads are sufficient. A big advantage is a long lifetime too, because they don´t contain any liquid electrolyte. Naturally, in devices, where high current peaks occur, it would be economically inefficient to use ceramic capacitors only. In such cases a combination of ceramic and tantalum or electrolytic capacitors is ideal.
In our offer can be found more types, also a novelty in our offer – 2,2uF/10V/0805 from the X7R mass from company YAGEO (please note a significantly lower price at purchase of 50 pcs and more). The X7R mass ensures very good properties in a wide range of temperatures and voltages. Detailed information will provide you the X7R, X5R and Y5V documents. In case of interest about any YAGEO component, please contact us at email@example.com
Do you utilize ceramic capacitors for power supply filtering? - [Link]
Useful life (also termed service life or operational life) is defined as the life achieved by the capacitor without exceeding a specified failure rate. Total failure or failure due parametric variation is considered to constitute the end of the useful life.
Depending on the circuit design, device failure due to parametric variation does not necessarily imply equipment failure. This means that the actual life of a capacitor may be longer than the specified useful life. Data on useful life has been obtained from experience gained in the field and from accelerated tests.
The useful life can be prolonged by operating the capacitor at loads below the rated values (e.g. lower operating voltage, current or ambient temperature) and by appropriate cooling measures. In addition to the standard type series, EPCOS types are available with useful life ratings specially matched to customer specifications.
Calculating the Useful Life of Capacitors - [Link]
A photoflash unit is a Resistor-Capacitor circuit. It utilizes a fundamental property of capacitors. A capacitor opposes an abrupt change in the voltage and this ability of a capacitor is put to use.
Circuit design of a photoflash unit:
A photoflash unit has a simple circuit design: a high-voltage direct current (DC) supply is connected in series with a high-resistance resistor (which we’ll call ‘R1′). This resistor limits the current flow. A capacitor ‘C’ is connected in parallel with a flash lamp. The resistance ‘R2’ of a flash lamp is of small value. The circuit contains a switch between the large resistance ‘R1’ and a small resistance flash lamp ‘R2’, such that it can connect either resistance at any time during the process.
How does it work?
When the switch connects R1, the capacitor begins to become charged. The charging of a capacitor is time consuming due to a large ‘time constant’. The time constant is the product of the resistance ‘R1’ and the capacitance ‘C’, given by the following expression:
Time Constant = Resistance of large Resistance * Capacitance
T = R1*C
During the charging process, the potential of the capacitor starts rising gradually. Initially it has the value of zero but by the charging it rises to a steady value of ‘Vs’. As the voltage increases, the value of the electric current passing through it decreases from peak value to zero. This limiting of current happens due to the large resistance R1. The charging time of a capacitor is approximately equal to five times the time constant. That is;
Charging time of capacitor = 5*Time constant
The discharging process of a capacitor takes place when switch connects with the flash lamp (with small resistance ‘R2’). The low resistance of the flash lamp allows a high discharge electric current to flow in a brief period of time. The discharging time is almost five times the product of small resistance ‘R2’ and the capacitance ‘C’, given by the following relation:
Discharging time of a capacitor = 5* (R2*C)
The photoflash unit circuit emits a high current pulse of short duration during the complete charging and discharging process of this simple Resistor- Capacitor Circuit. Such an RC circuit has many other practical applications, including Radar Transmitter Tubes and Electric Spot Welding.
If sensitive analog systems are run from one supply without the sufficient bypassing to eliminate noise, undesired degradation in a system’s performance will result. This application note provides insight into suitable techniques to overcome this roadblock.
You have combined digital and analog functions together in the final stage of a system design. But then the performance of the analog function, such as an audio amplifier, deteriorates due to the noise originating from the digital circuits. This can happen even after conventional preventive measures (e.g., separating analog and digital grounds, shielding) were taken. Noise interference problems can likely be traced to the coupling of power supplies, sometimes even if separate linear regulators are used.
Eliminate Noise Through Proper Supply Bypass Filtering - [Link]
Multilayer ceramic capacitors should be handled very carefully during mounting, soldering, and handling. Any damage incurred during these processes, no matter how small, can contribute to premature component failure. Handling a PCB with soldered components should be done with care to avoid any bending of the board. If steps outlined in this paper are followed, MLCC cracking can be avoided successfully.
Frequently asked questions about chip capacitor cracking - [Link]