Wednesday, December 15, 2010
【 Weak current College 】 capacitors using mistaken 】 on
1. tantalum capacitors for high reliability, why use a significant amount of time must be reduced?
Tantalum capacitor reliability refers to it in the stable or the experimental conditions, even after 10 years, it's basic electrical properties virtually no changes especially leakage current has been to maintain a very low level. Unlike other capacitors, extended over time, the basic performance will gradually deterioration in concrete using, because some circuit higher AC ripple and high DC surge, the switch is actually added to the capacitor voltage will in a very short period of time [generally less than 1 microsecond] jumped to more than the rated voltage of capacitor, the actual use, must be based on the circuit of surge height, to the maximum use of capacitor voltage to leave allowance. in basic use of tantalum capacitors, especially in circuit filtering circuit, there is the surge is a basic circuit, therefore, despite the reliability of the tantalum capacitor is relatively high, the use in the circuit must be significantly reduced for use before they can reach a higher reliability.
2. a ceramic capacitor is not easy to fail, the reliability is high.
In fact ceramic capacitor features its because the overlay will cancel each other out between inductance, capacitance change at high frequencies, and a smaller high-impedance small. Meanwhile, polarity, ripple good. these characteristics make it use to high-frequency circuit and AC signal circuit without rival.
When used in low frequency, if the product requires a high-temperature characteristics, ceramic capacitors, especially the MLCC laminated ceramic capacitor will not be the best choice from reliability, reliability is better than tantalum capacitors and oxidation of niobium capacitor low at least an order of magnitude.
If you are using pulse charging and discharging circuit, its too small in size and capacity and temperature characteristics will not be a tantalum and niobium oxide capacitors opponent.
In addition, laminated ceramic capacitor welding after crack problems can lead to circuit failure, at the same time find difficulties in proportion to its invalidation. Moreover is much higher than that of the tantalum capacitor.
3. ignore the ripple current in the capacitor reliability implications.
When using a polarity of electrolytic capacitors, everyone on the use of voltage and rated voltage is very sensitive, for the capacity you can directly select. existing on the circuit to circuit reliability of ripple affect almost universal awareness is not enough. ripple current actually refers to the DC circuit inevitable presence of AC current for a polar capacitors and circuit pipe and other power of the device, at the time of the adoption of the ripple current and voltage is high, will generate excessive heat and power loss if excessive ripple, but also very easy to use, or the operating temperature is high component appears suddenly fail.
As a capacitor's own resistance and volume is a must, therefore, it is through the ripple of thermal emission balance, in other words, different specifications of the product to be able to withstand AC ripple values differ. when the circuit in AC ripple values too high, a capacitor is fever, when the working temperature and time, or even explosion.
DC control circuits in high or low AC ripple values depends on the fore transformer or the quality of the rectifier, for use in switching power supply circuit capacitor reliability impact and uses the same voltage is deadly for the power supply module requires the use of other users, must give sufficient attention.
Otherwise, the capacitor will appear ' inexplicable ' failure. for purchased power module output AC ripple size requirements to the highest possible absolute cannot ignore this parameter on the circuit of the safety requirements.
4. small capacitor than bulky capacitors.
In the installation area and weight there is a clear requirement of circuit, some designers prefer the use of voltage and capacity of a certain volume of the product. Indeed, in the capacity and voltage must, bulky products of ESR values to lower, more pressure cushion, in strict limits on production volume of the product, its reliability is certainly below the large product-if you use a voltage of the circuit is very low, and the peak current is small, such as personal take use the phone and the Bluetooth headset, you must use the volume and quality of the capacitor can be as small as possible so that the design of power than in control when used on the device, if the installation area enough, select large product will have
Higher reliability is in the affirmative.
5. capacity options don't fit.
In voltage and volume determines, if you choose a larger product, its filtering characteristics will be better and higher resistance to surge capacity. only signal respond slower bit in switching power supply circuit using capacitors, if you can use the do not use 100UF 68UF products, circuit reliability may be higher for charging and discharging circuit using capacitors, this is all the more important.
In circuit design, designers should as far as possible on the various performance features and disadvantages of the capacitor research thoroughly, different kinds of capacitors have different advantages and disadvantages, if you want to ensure that your design circuit does not lead to unexpected behavior and properties of the component and understanding is required of the reliability of any electronic components are closely related to the specific conditions of use, the performance characteristics and a capacitor circuit characteristics match the capacitor reliability can be guaranteed. don't hope for own design selection when there is a problem with the reliability of the capacitor can also meet your requirements.
6. foreign countries than China's good.
Admittedly, China electronics production technology level there is a significant gap with the developed countries, but the gap is not just in all the specifications and models, all the same, the year after the introduction and independent development, the domestic many high technology product performance have reached the world level as well as electronic components, in-progress very quickly. many types of electronic components for quality in practice has reached the international level. Moreover present electronic bulk markets almost completely filled by foreign fakesRanching. If the quality directly from the official manufacturers ordering, quality or can guarantee.