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Default [KB6NU] 2020 Extra Class study guide: E6B - Diodes

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2020 Extra Class study guide: E6B - Diodes

Posted: 09 Feb 2020 06:06 AM PST

Diodes have two terminals and conduct current in only one direction, from
the cathode to the anode. By manipulating the characteristics of the
semiconductor material, manufacturers can make diodes useful in a wide
variety of applications.

Take, for example, the Zener diode. Zener diodes actually allow current to
flow in both directions, but only when the reverse bias voltage reaches a
specific voltage, called the Zener voltage. When the voltage across the
Zener diode reaches that point, it begins to conduct current in the reverse
direction and maintains a constant voltage drop across the diode. This
makes it useful in voltage regulator circuits.
QUESTION: What is the most useful characteristic of a Zener diode? (E6B01)

ANSWER: A constant voltage drop under conditions of varying current

Another example is the varactor diode. The capacitance of a varactor diodes
changes as you change the voltage across it. This allows you to use it as a
voltage-controlled capacitor in tuning circuits.
QUESTION: What type of semiconductor device is designed for use as a
voltage-controlled capacitor? (E6B04)

ANSWER: Varactor diode

PIN diodes are diodes that operate as a variable resistor at RF and
microwave frequencies. One common use for PIN diodes is as an RF switch.
One characteristic of a PIN diode that makes it useful as an RF switch or
attenuator is low junction capacitance. The forward DC bias current level
is used to control the attenuation of RF signals by a PIN diode.
QUESTION: What characteristic of a PIN diode makes it useful as an RF
switch? (E6B05)

ANSWER: Low junction capacitance
QUESTION: What is used to control the attenuation of RF signals by a PIN
diode? (E6B11)

ANSWER: Forward DC bias current

Schottky diodes have a metal-semiconductor junction and have less forward
voltage drop than other types of diodes. For this reason, are often used as
a power supply rectifier. When used in digital ICs, the lower forward
voltage drop allow the ICs to switch faster, and they are also often used
as a VHF/UHF mixer or detector.
QUESTION: What is an important characteristic of a Schottky diode as
compared to an ordinary silicon diode when used as a power supply
rectifier? (E6B02)

ANSWER: Less forward voltage drop
QUESTION: Which of the following is a Schottky barrier diode? (E6B08)

ANSWER: Metal-semiconductor junction
QUESTION: Which of the following is a common use of a Schottky diode?

ANSWER: As a VHF/UHF mixer or detector

Point-contact diodes are also commonly used as RF detectors.
QUESTION: What is a common use for point-contact diodes? (E6B09)

ANSWER: As an RF detector

Light-emitting diodes, or LEDs, are widely used in amateur radio as visual
indicators. When you forward bias an LED, current flows through the diode
and it emits light. The schematic symbol for an LED is similar to the
symbol for a signal diode, but has two arrows pointing away from the diode
that are meant to show that it is emitting light.
QUESTION: What type of bias is required for an LED to emit light? (E6B03)

ANSWER: Forward bias
QUESTION: In Figure E6-2, what is the schematic symbol for a light-emitting
diode? (E6B10)


No matter what type of diode you are using, it’s very important to not
exceed the forward current specification. Doing so, will cause the junction
temperature to increase, and ultimately cause the diode to fail.
QUESTION: What is the failure mechanism when a junction diode fails due to
excessive current? (E6B07)

ANSWER: Excessive junction temperature

The post 2020 Extra Class study guide: E6B Diodes appeared first on KB6NUs
Ham Radio Blog.

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