Ceramic capacitors are divided into two distinctive types according to structure, monolithic and disc type.
The disc type ceramic capacitors are made with a wide range of voltage, tolerances and temperature coefficients.
They are produced in both AC and DC voltages.
The DC rated voltages are more popular and are categorized as Class I, Class II and Class III types.
The AC rated discs are considered Safety Recognized capacitors.
Class I is a temperature compensating disc capacitor. This type of ceramic capacitor is suitable for resonant circuit applications or other applications where high quality and predictable stability of capacitance characteristics are required. These capacitors have temperature coefficients ranging from P100 to N750 and utilize lower dielectric constant ceramics. Voltage ratings generally range from 500VDC to 30KVDC. Temperature coefficients are indicated with the 3 digit code per EIA RS-198.
|C0||G = 30PPM||NPO|
|U1||H = 60PPM||N080|
|P2||J = 120PPM||N150|
|R2||K = 250PPM||N220|
|S2||L = 500PPM||N330|
|T2||M = 1000PPM||N470|
|U2||N = 2500PPM||N750|
This chart indicates a linear and retraceable change with temperature, expressed in parts per million per ºC temperature change. An example is N750 states a nominal change of 750 / 1,000,000 parts or .075% decrease for each ºC increase in temperature. The high capacitance stability coupled with its long life makes this style of capacitor ideally suited for UHF and VHF applications. The strong phenolic coating and varying lead configurations adapt to both auto and hand insertation.
Class II is considered to be a semi stable capacitor. Units indicated as EIA Class II exhibit non-linear changes with temperature and a significant dependence on voltage and frequency. The method used to specify the dielectric constants is 3 symbol codes to describe the maximum allowable change between high and low temperatures. The first letter indicates low temperature of interest. The second digit indicates the high temperature of interest. The third and final symbol indicates the maximum temperature change form the 25ºC that is allowed at those temperatures.
|LETTER SYMBOL||LOW TEMP. REQUIREMENT||NUMBER SYMBOL||HIGH TEMP. REQUIREMENT||LETTER SYMBOL||MAX. CAPACITANCE CHANGE OVER TEMP. RATING|
|T||± 22% -33%|
|7||+125ºC||U||± 22% -56%|
|V||± 22% -82%|
Class III are considered general purpose capacitors. They are identical to Class II capacitors except that it is restricted to those values which vary by more than %15 with changes in temperature over the rated temperature range. This style of capacitor is most often used in by-pass and coupling applications and in other applications where dielectric losses, high insulation resistance and capacitance stability are not a major consideration. They are designed to operate with the same temperature limits set by the EIA code used for Class II capacitors. Storage temperature may vary between -55ºC to +125ºC without affecting ratings.