30-08-2019, 08:21 AM
(This post was last modified: 30-08-2019, 08:23 AM by Mike Watterson.)
There are differing types of ceramic. Only some types are replacement for silver mica or polystyrene. It's not just construction, voltage rating and temperature coefficient, but also microphony due to piezo effects, which also can result in non-linear capacitance with voltage. In general the ones that replace silver mica or polystyrene are much larger per pF and are available in NPO as well as various defined positive or negative coefficients. The general purpose ones to replace metalised polyester are not available at much more than 150V. There are multlayer type for low voltages to get up to 1uF in a very small package. There are ones that are X & Y rated at the same time, 100pF to 10nF and 1, 2 or 4 kV that can be very large if 4kV. Tolerance can be 1% to 80% depending on dielectric.
Tantalum capacitors are mainly only for 1uF to 100uF where very very low leakage and tighter tolerance is needed. There are several kinds. Otherwise Aluminium Electrolytic are used. The Aluminium Electrolytic are used only for 0.1uF to 1uF instead of plastic or ceramic were tolerance and leakage don't matter and higher voltage in small size is needed. Mostly replaced by multilayer SMT ceramic in 1.8V to 16V circuits and now only used for more than 15V.
Bipolar are rubbish, they are Aluminium Electrolytic. Better to use metalised polyester (metpoly) as replacements and new builds.
Frequency:
This is about dielectric material and size. The smaller ceramic caps have a dielectric unsuitable for RF. Professional radio gear might have an Aluminium Electrolytic, a 0.1uF Z5U dielectric, a 2nF X7R and a 100pF ??? all in parallel.
Z5U = non-RF coupling or decoupling. Often 20% to 50% tolerance. Quite piezo-electric. Most 0.1uF are this material
X7R = General purpose dielectric. Can be 10%. Many but not all 10nF are this material.
There are many ceramic materials used as dielectric.
Tantalum capacitors are mainly only for 1uF to 100uF where very very low leakage and tighter tolerance is needed. There are several kinds. Otherwise Aluminium Electrolytic are used. The Aluminium Electrolytic are used only for 0.1uF to 1uF instead of plastic or ceramic were tolerance and leakage don't matter and higher voltage in small size is needed. Mostly replaced by multilayer SMT ceramic in 1.8V to 16V circuits and now only used for more than 15V.
Bipolar are rubbish, they are Aluminium Electrolytic. Better to use metalised polyester (metpoly) as replacements and new builds.
Frequency:
This is about dielectric material and size. The smaller ceramic caps have a dielectric unsuitable for RF. Professional radio gear might have an Aluminium Electrolytic, a 0.1uF Z5U dielectric, a 2nF X7R and a 100pF ??? all in parallel.
Z5U = non-RF coupling or decoupling. Often 20% to 50% tolerance. Quite piezo-electric. Most 0.1uF are this material
X7R = General purpose dielectric. Can be 10%. Many but not all 10nF are this material.
There are many ceramic materials used as dielectric.
