Voltage rating is usually marked and is
often identified by the symbol V. Most electrolytic capacitors
clearly indicate their voltage rating. Polyester capacitors
usually show the voltage rating but often omit the V symbol.
Small ceramic capacitors often show no voltage rating. If the
capacitance and voltage rating are both marked, a unit is also
marked for at least one of the quantities so that the two cannot
be confused.
Tolerance indicates how close a capacitor’s actual
value is likely to be over or under its marked value. It is
usually expressed as ±%.
Polarity sensitive capacitors, such as electrolytics,
are usually marked with a + or - symbol adjacent to one lead
to indicate polarity.
All real capacitors exhibit some change in value with
varying temperature. Some ceramic types exhibit fairly linear
changes and are useful as temperature compensating elements
in AC circuits. The temperature coefficients of these types
may be marked in letter codes or designated by a colour spot.
| KP |
Polypropylene film/foil |
| KS |
Polystyrene film/foil |
| KT |
Polyester film/foil
(polyethylene terephthalate PETP) |
| MK |
Metallised plastic film
(general) |
| MKP |
Metallised polypropylene |
| MKT |
Metallised polyester
(polyethylene terephthalate PETP) |
| MKT-P |
Metallised polyester/paper |
| MKY |
Metallised low-loss
polypropylene |
| MKL |
(MKU) Metallised lacquer
(cellulose acetate) |
|
|
These offer low cost and high capacitance
in a small physical size. Normally there are two types, the
‘High Stability Temperature Compensating’ type and the ‘Bypass
and Coupling’ type. The former is for use in resonant circuit
and filter applications, with a value largely independent of
voltage and frequency. The latter is for use in less critical
applications, as they are less stable and have non-linear temperature
characteristics and are somewhat voltage dependent.
This type offer good stability, a large range of values
at low cost and are the most widely used capacitor for general
applications.
These offer tight tolerance and are highly stable,
making them suitable for very stable tuned circuits and oscillators.
Polystyrene is now an obsolete material and is being replaced
by polypropylene capacitors in more and more applications. There
is still a supply of polystyrene available on the market, but
unfortunately the prices are likely to rise over the coming
months and years. We at Maplin have, however, managed to secure
a supply of polystyrene capacitors for at least the next 5 years
and will endeavour to keep the prices stable for as long as
possible.
This type have a very low dielectric loss
and are particularly suitable in audio circuits and sample-and-hold
circuits. They are also an ideal alternative to polystyrene
capacitors.
Ideal for use in filtering and smoothing applications
in power supplies. Also used for coupling and bypassing in audio
circuits and as a timing element in non-critical circuits. They
have a high reliability and low leakage. Since all electrolytic
capacitors have a wide tolerance, one of the capacitors in our
range will suffice in most cases where an electrolytic is specified.
Choose the nearest value to the one specified and the nearest
voltage equal to or above the one specified, e.g.: 50µF at 50V
specified, nearest value 47µF and 100V is the nearest voltage
above. Thus a 47µF at 100V will perform the same job as a 50µF
at 50V in almost all applications, provided its physical size
is not too large.
These are an ideal alternative to electrolytic
capacitors, as they offer a smaller size and lower leakage. |
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