Red GaAsP LED: 1.3V
Blue InGaN LED: 3.0V
Using the diode setting, you can
usually identify the type of diode
or junction transistor, as well as
determine if it's open or shorted.
BTW, thanks for asking that
question which inspired me to check
the open-circuit voltage and current
draw of my DVM diode and resistance
settings. Now, my measurements
should be a bit more meaningful.
#2 The "diode" range on digital
multimeters is used to "measure"
diodes (any type) to see if they are
good or not. To use the range,
connect the BLACK meter lead to the
diode wire with the "stripe" on the
diode body (cathode lead) and the
RED meter lead to the other diode
wire (anode lead). The following are
"typical good" forward-bias readings
for various diodes:
• Silicon diodes: 0.6-0.7
• Germanium diodes: 0.3-0.4
• Tunnel and Schottky diodes:
• Zener diodes: Similar to silicon
• Selenium rectifier: 0.9-1.2
• Power (i.e., 10A rating) and high
voltage (i.e., kilovolt rating) diodes:
• LEDs: 1.6-1.8
Reversing the leads (
reverse-biasing) will show "OL" — any "numerical"
reading usually indicates the diode is
shorted in reverse-bias. This range is
also useful for checking the polarity of
bipolar (PNP, NPN) transistors, if you
don't know what kind you have:
• The emitter-base drop will read
• The collector-base drop will read
• The collector-emitter junction will
read OL (anything less indicates a
• Reverse-bias the emitter-base and
collector-base junctions and you'll
read OL (anything less indicates a
NOTE: The BLACK lead will tell
you which lead(s) are the N lead(s) for
determining PNP or NPN polarity
(use the voltage drop difference to
determine collector from emitter). It's
also useful for determining the
polarity of unmarked diodes: BLACK
is cathode (stripe) and RED is
ANODE. DO NOT use this range to
measure FETs (field-effect transistors)
as modern FETs are "static-sensitive"
devices and will probably be
destroyed from the action of taking
the reading. SCRs, triacs (i.e., thyristors), and similar exotic junction-type
devices cannot be accurately tested
on this range. Finally, you can measure
low value resistors (< 2,000 ohms); the
range usually has a buzzer associated
with it for audible continuity readings
(i.e., wire tracing, testing fuses).
[#8132 - August 2013]
How do the different types
of capacitors (ceramic, electrolytic,
tantalum, etc.) differ and why would
you use one type over another in a
#1 There are many types of
capacitors in common use today, with
many different properties. The key
difference is the dielectric — or insulating material — between two metal
plates. Here are some common types.
All values shown are just rough
approximations. Maximum capacity
is expressed as nF (nanofarad), µF
(microfarad), and F (Farad); maximum
voltage as V (volt) or kV (kilovolt); and
maximum frequency as Hz (Hertz),
kHz (kiloHertz), or MHz (megaHertz).
Air variable capacitor: Used in
radio receivers and low power transmitters. Value may be changed, but
bulky for capacity. Max. ~1 nF,
~1,000V, ~100 MHz.
Vacuum variable capacitor: Used
in high power transmitters. Value may
be changed, but bulky for capacity.
Max. ~1 nF, 10,000 V, ~1,000 MHz.
Mica capacitor: Used in receivers
and transmitters. Value is stable. Max.
~1 nF, ~1,000V, ~1,000 MHz.
Ceramic capacitor: Used in
digital electronics, receivers, and
transmitters. Value is less stable than
mica, but more compact. Max. ~1 µF,
~1,000V, ~1,000 MHz.
Al or Ta electrolytic capacitor:
Used in audio frequency and power
supplies. Al is cheap; Ta is more
efficient. All require a DC offset and
are destroyed by true AC or reverse
voltage. Max. ~100,000 µF, ~300V,
~ 30,000 Hz.
dielectric capacitors for power
supplies and power backup. It offers
very high capacity, and might
eventually approach that of electrochemical cells, but has low voltage per
capacitor, so are usually placed in
series. Max. ~100 F, ~1V, ~100 Hz.
Other dielectrics are used, such as
paper, plastics, glass, and water (yes,
pure water has a high dielectric
constant, low conductivity, and
is environmentally friendly). Check out
#2 Ceramic caps are small, low loss,
low leakage, and inexpensive, but the
temperature coefficient varies
from COG (very stable, 2% is
available) to X7R (moderately stable,
10% is available) to Z5U (typically
+20%, -80% over temperature). There
is another type of ceramic called
porcelain that is used in microwave
applications; ordinary ceramics are
too lossy at those frequencies.
Aluminum electrolytics are widely
used because they are low cost
and smaller than a film capacitor.
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September 2013 79