Figure 5. An example
of even loops of bifilar coils,
conjectured in a manner that
when pulsed with AC electrical
current, it tends to partially —
if not almost totally — nullify the
(Source: Don E Mitchell Esoterica Images)
you can partially minimize this
inductance by winding wire in
sections in a reversed direction. This
practice is called bifilar winding and
helps to cancel fields (Figure 5).
Bifilar winding is a winding of
two adjacent insulated wires with
currents purposely traveling through
them in opposite directions for their
field cancelling effect.
coefficients of five to 25 ppm/oC.
Thin film resistors are more
expensive than thick film resistors.
The MELF (Metal Electrode Leadless
Face) resistors often use this same
technology; however, they are
cylindrically shaped resistors that
only come in surface-mount [SMD]
packages. Also, unlike thin film
resistors, their resistance value
results from cutting a helix through
the coating rather than by etching.
This special alloy foil is several
micrometers thick and allows resistor
manufacturers to make them with the
greatest accuracy and stability. Felix
Zandman of Vishay introduced Bulk
metal foil resistors in 1962.
Figure 6. The resistor color code
identifying each column used.
These have a metal wire
wrapped around a ceramic, plastic,
or fiberglass core. Two soldered
end caps attach the wire to the
core. The assembly usually has a
baked-on enamel coating protecting
it. Check out Figure 4. These
are usually power dissipation
devices and sometimes come
with heatsinks. Coiled wirewound
resistors innately possess
undesirable inductance; however,
Figure 7. Resistors
used in a simple voltage
Values of resistors most
commonly correspond to a color
coding scheme (Figure 6). The less
expensive ones have four bands with
the first two band’s significant figures
followed by a multiplier and possibly
a tolerance band. Therefore, a red,
red, and red would be 2,200 ohms
since the first two reds are two,
followed by two, and then it is 10
to the second power or 22 x 100
= 2,200 ohms. No band after that
assumes it is a 10% tolerance.
You use resistors in a myriad of
ways, realizing that a voltage drop
Figure 8. A simplified example illustrating the concept of a
voltage drop across a resistor versus its proportional value in a series
string of resistors.