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CAPACITORS 393

As with resistors, what’s printed on a capacitor may not exactly match its real value. The
ON THE
accuracy of the stated value can vary widely, typically much more than with resistors. There are
several ways to indicate capacitor tolerance. Rather than take up the space here, I’ve uploaded
W E B
a guide on capacitor selection to the RBB Online Support site, described in Appendix A.
Dielectric Breakdown Voltage Value
The dielectric breakdown voltage is specified only for certain capacitors. For those that have
it, the voltage is marked directly, such as “35” or “35V.” Sometimes, the letters WV are used
after the voltage rating. This indicates the working voltage. You should not use the capacitor
in a circuit with a voltage that exceeds this value.
On capacitors without a breakdown voltage printed on them you must estimate the value
based on the type of dielectric it uses. This is an advanced topic and not covered in this book;
nevertheless, it seldom comes up in electronics for robotics because most circuits use 12 volts
or less, and most capacitors have a rated breakdown voltage of 25 to 35 volts. As a safety
margin, select a capacitor with a breakdown voltage at least double the operating voltage of
the circuit.

Polarization Marking
Some capacitors are polarized. Markings on the capacitor indicate the + or the terminal.
If a capacitor is polarized, it is extremely important that you follow the proper orientation
when you install the capacitor in the circuit. If you reverse the leads to the capacitor— connecting
the + side to the ground rail, for example— the capacitor may be ruined. Other components
in the circuit could also be damaged.

G By convention, the polarizing mark on aluminum electrolytic capacitors is typically the
(negative) lead. The polarizing mark on tantalum electrolytic capacitors is typically the +
(positive) lead.

UNDERSTANDING CAPACITOR DIELECTRIC MATERIAL

Capacitors are classified by the dielectric material they use. The most common dielectric
materials are listed in Table 31- 3. The dielectric material used in a capacitor partly determines
which applications it should be used for.

COMMON APPLICATIONS FOR CAPACITORS
Unlike resistors, for which it’s easy to demonstrate practical applications in a circuit, capaci-
tors are a bit more nebulous. They tend to work by interacting with other components, rather
than doing things just on their own.
Capacitors are often used to filter, or remove, the rapid variations of an input voltage, leav-
ing only a steady voltage. This is quite useful in all kinds of electronics, because some compo-
nents produce large, instantaneous “glitches” of voltage. These glitches, referred to as power
line noise, may disrupt neighboring components, especially integrated circuits.
Capacitors may also be used with resistors as part of a timing circuit. The value of the
capacitor determines how long an event lasts— timing is controlled by how long it takes for
the capacitor to charge or discharge its current. In all of the applications in this book involving

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