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The question arises all the time concerning which capacitor type to use for a particular
application. This table provides a guideline for starters, but is in no way exhaustive. (DA
= dielectric absorption)
The unofficial temperature coefficient designations for the capacitors are as follows:
The temperature coefficient is given as "P" for positive, "N" for negative, followed by a
3-digit value of the temperature coefficient in ppm/°C. For example "N220", is -200 ppm/°C,
and "P100" is +100 ppm/°C. The one exception in this system is "NPO" where an "O" instead
of "0" is used, but quite a number of people use "NP0." In any event "NPO" means stable with
temperature.
| NPO Ceramic (COG) |
<0.1% |
Tight tolerance High Q factor, low K Small case size Inexpensive Good stability
Wide range of values Low inductance |
DA generally low, but may not be specified Limited to small values (10 nF) |
Low loss, timing and tuning applications |
| Monolithic Ceramic (High K) |
>0.2% |
Low inductance Wide range of values |
Poor stability Poor DA High voltage coefficient |
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| X7R (BX) (Barium Titanate) |
|
Inexpensive Low DA available Wide range of values Smaller case size |
Damaged by temperature >+85° C Loose tolerances High inductance |
Bypassing, coupling, and frequency discrimination circuits |
| Z5U & Y5V |
|
Smallest case size Very large values |
Damaged by voltages >25 WVDC Very loose tolerances |
Bypassing and coupling |
| Polystyrene |
0.001% to 0.02% |
Inexpensive Low DA available Wide range of values Good stability |
Damaged by temperature >+85° C Large case size High inductance |
Timers and filters |
| Polypropylene |
0.001% to 0.02% |
Inexpensive Low DA available High dielectric strength Wide range of values
Negative TC |
Damaged by temperature >+105° C Large case size High inductance |
Stable oscillators and filters, sample and hold circuits and pulse handling circuits |
| Teflon |
0.003% to 0.02% |
Low DA available Excellent stability Operational >+125° C Wide range of values |
Relatively expensive Large size High inductance |
Timing and pulse shaping circuits |
| MOS |
0.01% |
Good DA Small Operational above +125° C Low inductance |
Limited availability Available only in small capacitance values |
|
| Polycarbonate |
0.1% |
Good long-term stability Low cost Wide temperature range |
Large size DA limits to 8-bit applications High inductance |
Timers, filters and applications in high ambient temperature |
| Polyester |
0.3% to 0.5% |
Moderate stability Low cost Wide temperature range Low inductance (stacked film)
Self-healing |
Large size DA limits to 8-bit applications High inductance |
Bypassing and coupling |
| Mica |
>0.003% |
Low loss at HF Low inductance Very stable Available in 1% values or better |
Quite large Low values (<10 nF) Expensive |
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| Aluminum Electrolytic |
High |
Large values High currents High voltages Small size |
High leakage Usually polarized Poor stability Poor accuracy Inductive |
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| Tantalum Electrolytic |
High |
Small size Large values Medium inductance High melting point High dielectric
strength Good ductility |
Quite high leakage Usually polarized Expensive Poor stability Poor accuracy |
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Related Pages on RF Cafe - Capacitors &
Capacitance Calculations -
Capacitor
Color Codes - Capacitance Conversions -
Capacitor Dielectrics -
Standard Capacitor Values -
Capacitor Vendors -
The Noble Art of De-Coupling
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