Page 44 - Troubleshooting Analog Circuits

Don't Exceed Your Pot's I and V Ratings 31

2 5M 2 5M 2 5M 2 5M

03 PF 03 PF 0.3 PF 0.3 pF
(b) 1OM
-cJ-

DF
008

Figure 3.3. You can reduce the capacitance of a single resistor (a) by using several resistors in series as
shown in (b) (assume the inductance is negligible). This series resistor configuration has one-
fourth of the single resistor's capacitance (c) and extends the resistor's frequency response as
shown in (d).

of 2 to 4 worse than a single-turn pot because the mechanical layout of a single-tum
pot is more stable and balanced. Does anyone know of an example in which the
multi-turn pot is better? A full year after this statement was originally published.
nobody has tried to contradict me, although people who sell multi-turn pots still brag
in the vaguest possible terms about "infinite resolution"-bleah!

Don't Exceed Your Pot's I and V Ratings
How do variable resistors fail'? If you put a constant voltage between the wiper and
one end and turn the resistance way down. you will exceed the maximum wiper cur-
rent rating and soon damage or destroy the wiper contact. Note that the power rating
of most variable resistors is based on the assumption that the power dissipation is
uniformly distributed over the entire element. If half of the element is required to
dissipate the device's rated power. the pot may last for a short while. However. if a