Ceramic Capacitor
Ceramic Capacitors HF use
Ceramic capacitors are suitable for moderately high-frequency work (into the high hundreds of megahertz range, or, with great care, into the low gigahertz range), as modern ceramic capacitors are fairly non-inductive compared to the other major classes of capacitors (film and electrolytic). Capacitor technologies with higher self-resonant frequencies tend to be expensive and esoteric (typically, mica or glass capacitors).
Ceramic capacitors come in various shapes and styles
- disc, resin coated, with through-hole leads
- multilayer rectangular block, surface mount
- bare leadless disc, sits in a slot in the PCB and is soldered in place, used for UHF work
- tube shape, not popular now
- EEStor's high capacitance barium titanate "EESU" designed for electric vehicles is a ceramic capacitor.
Classes of ceramic capacitors
Class I capacitors: accurate, temperature-compensating capacitors. They are the most stable over voltage, temperature, and to some extent, frequency. They also have the lowest losses. On the other hand, they have the lowest volumetric efficiency. A typical class I capacitor will have a temperature coefficient of 30ppm/C. This will typically be fairly linear with temperature. These also allow for high Q filters - a typical class I capacitor will have a dissipation factor of 0.15%. Very high accuracy (~1%) class I capacitors are available (typical ones will be 5% or 10%). The highest accuracy class 1 capacitors are designated C0G or NP0.
Class II capacitors: better volumetric efficiency, but lower accuracy and stability. A typical class II capacitor may change capacitance by 15% over a -55C to 85C temperature range. A typical class II capacitor will have a dissipation factor of 2.5%. It will have average to poor accuracy (from 10% down to +20/-80%).
Class III capacitors: high volumetric efficiency, but poor accuracy and stability. A typical class III capacitor will change capacitance by -22% to +56% over a temperature range of 10C-55C. It will have a dissipation factor of 4%. It will have fairly poor accuracy (commonly, 20%, or +80/-20%). These are typically used as decoupling or in other power supply applications.
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