Electronic Restoration >> Smoke Damage Restoration For Electronics

In Figure 17, the dashed vertical line represents the typical DC leakage current limit for a 150µF, 6.3V device while the solid vertical line represents the limit for a tantalum polymer device. It's clear that one of these capacitors would not have met the MnO2 limit and Smoke Damage Restoration For Electronics several others are pretty close. This is typical for tantalum polymer capacitors from all manufacturers. 

Tantalum polymer capacitors generally have much higher leakage current than is true for comparable MnO2-based capacitors, Smoke Damage Restoration For Electronics and the median value of the distribution is usually closer to the catalog limit for tantalum polymer capacitors than is true for MnO2-based capacitors. Typical impedance and ESR data for a KEMET 330µF, 6.3V tantalum polymer capacitor appear in the swept-frequency plot of Figure 18. 

This plot was generated with the KEMET-Spice capacitor modeling program that is available without cost to customers. Similar software is available from other manufacturers as well. While the data of Figure 18 are not laboratory-measured data, Smoke Damage Restoration For Electronics they are remarkably similar to such laboratory-measured data.In addition to interactive graphs.

The software can provide numerical values for the discrete components ofan equivalent electronic circuit that behaves very much like the actual capacitors over a wide range of Smoke Damage Restoration For Electronics frequencies. These equivalent circuit models can then be incorporated into a larger computer models of acustomer's circuit to simulate expected capacitor behavior over wide ranges of frequency, temperature, andvoltage. 

These models are typically based on the RC-ladder structure that was schematically described in Figure 5. Generally speaking, Smoke Damage Restoration For Electronics there is little difference in the overall appearance of impedance and ESR graphs for tantalum polymer capacitors and MnO2-based tantalum capacitors, with the exception that the ESR is lower for the tantalum polymer capacitors at frequencies above roughly 1kHz. 

These lower ESR values reflectthe improved conductivity of the polymer cathode material. Near resonance, Smoke Damage Restoration For Electronics the impedance values for tantalum polymer capacitors are lower than for MnO2-based tantalum capacitors, reflecting the lower ESR. However, the impedance away from resonance is essentially similar for both polymer- and MnO2-cathode devices. 

The downward slope of the impedance curve priorto resonance is dominated by the capacitive reactance and Smoke Damage Restoration For Electronics the upward slope after resonance is dominated by inductive reactance. These parameters are similar for both capacitor styles. Figure 19 presents a comparison of the capacitance roll-off behavior of various styles of tantalum capacitors. 

It was stated earlier that less capacitance roll-off is observed Smoke Damage Restoration For Electronics at a given high frequency if theresistance values in the RC-ladder of Figure 5 are lower as would be the case for use of a conductivepolymer cathode having higher conductivity than MnO2. Less capacitance roll-off is also observed if the physical length of the ladder is shortened. 

This is analogous to reduced loss in a short transmission lineversus a longer transmission line fabricated from the same materials. Both of these concepts are validated by the data of Figure 19. The most poorly performing device is the single-anode MnO2-based capacitor which Smoke Damage Restoration For Electronics demonstrates initiation of roll-off slightly above 1kHz. 

If thesingle MnO2-based capacitor element is replaced by three very thin MnO2-based elements connected inparallel, Smoke Damage Restoration For Electronics significant roll-off doesn't occur until frequencies above 10kHz. This demonstrates the beneficialeffect of reducing the length of the RC-ladder structure by making the capacitor elements thinner.

The remaining curve demonstrates the superior performance that is achieved by combining the Smoke Damage Restoration For Electronics benefits of multiple thin capacitor elements with the conductivity enhancement provided by the conducting polymer.It is expected that a single-anode tantalum polymer device would have performed similarly to the multipleanode MnO2 device, but the multiple-anode tantalum polymer capacitor demonstrates clearly superiorperformance. 

For this capacitor, significant roll-off is postponed Smoke Damage Restoration For Electronics until frequencies well above 100kHz. Typical Dielectric Robustness Not all tantalum capacitors from a given lot have similar dielectric robustness. It is not unusual for thebreakdown voltages during rapid charging to vary over a range of 2:1 to 3:1 or more. 

Of course there is not much concern about the devices at the high end of the range, Smoke Damage Restoration For Electronics it is the relatively few at the low end of therange that cause almost all of the problems with turn-on failures.Figure 20 contains dielectric breakdown data collected on large samples of 220µF, 10V, MnO2-basedtantalum capacitors. 

There are 5 curves that represent statistical distributions of breakdown voltage whenlarge samples of capacitors from a randomized population were rapidly charged through various seriesresistances (the resistance includes the capacitor's ESR). Although not specifically pertinent to the topic athand, it is clear from the data that the breakdown voltages are significantly affected by the value of seriesresistance, Smoke Damage Restoration For Electronics this effect can be quantified, and higher series resistance leads to higher breakdown voltages.

For a value of total series resistance of 0.35Ω, Smoke Damage Restoration For Electronics it is seen that the breakdown voltages range from 8V to 26Vor 0.8 to 2.6 times rated voltage, a range of 3.25:1. This is fairly typical performance for MnO2-based tantalum capacitors. Had these capacitors been 100% surge current tested at full rated voltage duringproduction testing, probably none of the capacitors would have failed below rated voltage. 

This wouldhave tightened the range to 2.6:1. In contrast, Smoke Damage Restoration For Electronics Sanyo provided similarly-collected breakdown data for some 150µF, 10V tantalum polymercapacitors. These data appear in Figure 21 and are generally representative of 10V tantalum polymercapacitors.The external series resistance was 0.33Ω and it is estimated that the ESR of the capacitors was roughly 20mΩ. 

Thus the total series resistance was approximately 0.35Ω, the same total series resistance as wasused to generate the 0.35Ω MnO2-based curve of Figure 20. The range of breakdown voltages is 1.75 to 2.6 times rated voltage, Smoke Damage Restoration For Electronics or roughly 1.5:1. This is a much smaller spread of breakdown voltages than wasseen for the MnO2-based tantalum capacitors in Figure 20. 

It is common that the range of breakdownvoltages for tantalum polymer capacitors is smaller than observed for MnO2-based devices Smoke Damage Restoration For Electronics and that the firstbreakdown occurs at much higher voltage. The first significant observation is that both styles of capacitors had maximum breakdown voltage of 2.6 times rated voltage. 

While this exact agreement is probably coincidental, the similarity of the values is note worthy, Smoke Damage Restoration For Electronics and likely represents the existence of an upper limit to dielectric robustness that is related to the dielectric formation voltage (likely to be in the neighborhood of 3 times rated voltage).

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