Capacitor Information
Here is some information I have collected off the web, initially to
help in the choice of HV decoupling caps for the ATLAS MDTs.
Much of the information about di-electrics was distilled from the very useful
Novacap web site .
Di-Electric Types
Class I (NPO)
- Formulated mostly of TiO2
- Quite linear with temperature, very low tempco
- Low capacitance vs voltage dependance
- Relatively flat frequency response
- No significant ageing
- Relatively low dielectric constants (<150)
See Novacap
for more information. The most common spec is COG (or NPO) which is
0 PPM/oC +/- 30 PPM/oC.
"COG" Codes for identification of Class I dielectrics:
Class II Dielectrics (X7R, Z5U, Y5V etc)
- Ferro-electric ceramics
- Tempco typically +/-15% over temp range
- Significant capacitance vs voltage dependance (but details depend on construction)
- Significant drop in C at high frequencies
- Significant ageing (2%-5% drop in C per decade-hour)
- High dielectric constants (600-4000)
See Novacap for more information.
Special category "BX" is defined by Mil spec. This type is
rated for maximum capacitance change of +15%/-25% over complete temp and voltage range.
"X7R" Codes for identification of Class II dielectrics:
