Handbook for Sound Engineers

Resistors, Capacitors, and Inductors 261

electrolyte in intimate contact with the capacitor
cathode. A suitable end seal arrangement prevents the
loss of the electrolyte.
Wet-slug tantalum capacitors are manufactured in a
working voltage range up to 150 Vdc.

Solid-Electrolyte Sintered Anode Tantalum Capaci-
tors. Solid-electrolyte sintered anode tantalum capaci-
tors differ from the wet versions in their electrolyte.
Here, the electrolyte is manganese dioxide, which is
formed on the tantalum pentoxide dielectric layer by
impregnating the pellet with a solution of manganous
nitrate. The pellets are then heated in an oven and the
manganous nitrate is converted to manganese dioxide.
The pellet is next coated with graphite followed by a
layer of metallic silver, which provides a solderable
surface between the pellet and its can.
The pellets, with lead wire and header attached, are
inserted into the can where the pellet is held in place by
solder. The can cover is also soldered into place.
Another variation of the solid-electrolyte tantalum
capacitor encases the element in plastic resins, such as
epoxy materials. It offers excellent reliability and high
stability for consumer and commercial electronics with
the added feature of low cost.
Still other designs of solid tantalum capacitors, as
they are commonly known, use plastic film or sleeving
as the encasing material and others use metal shells
which are back filled with an epoxy resin. And, of
course, there are small tubular and rectangular molded
plastic encasements as well.

Tantalum Capacitors. In choosing between the three
basic types of tantalum capacitors, the circuit designer
customarily uses foil tantalum capacitors only where
high voltage constructions are required or where there is
substantial reverse voltage applied to a capacitor during
circuit operation.
Wet-electrolyte sintered anode capacitors, or
wet-slug tantalum capacitors, are used where the lowest
dc leakage is required. The conventional silver can
design will not tolerate any reverse voltages. However,
in military or aerospace applications, tantalum cases are
used instead of silver cases where utmost reliability is
desired. The tantalum-cased wet-slug units will with-
stand reverse voltages up to 3 V, will operate under
higher ripple currents, and can be used at temperatures
up to 200°C (392°F).
Solid-electrolyte designs are the least expensive for a
given rating and are used in many applications where
their very small size for a given unit of capacitance is
important. They will typically withstand up to 15% of
the rated dc working voltage in a reverse direction.

They also have good low temperature performance

characteristics and freedom from corrosive electrolytes.

10.2.4.6 Suppression Capacitors

Suppression capacitors are used to reduce interference

that comes in or out through the power line. They are

effective because they are frequency dependent in that

they become a short circuit at radio frequencies, without

affecting low frequencies. Suppression capacitors are

identified as X capacitors and Y capacitors. Fig. 10-22

shows two examples of radio interference suppression.

Fig.10-22A is for protection class I which would

include drills and hair dryers. Fig.10-22B is for protec-

tion class II where no protective conductor is connected

to the metal case G.

X Capacitors. X capacitors are used across the mains

to reduce symmetrical interference where a failure in

the capacitor—i.e., the capacitor shorts out—will not

cause injury, shock or death.

Y Capacitors. Y capacitors are used between a live

conductor and a cabinet or case to reduce asymmetrical

Figure 10-22. Radio frequency suppression with X and Y

capacitors. Courtesy of Vishay Roederstein.

G

N

L

PE

Line

Cy

Cy

Cx

G

N

L

Line

Cy

Cy

Cx

A. Protective class I

B. Protective class II