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Subelement E6
CIRCUIT COMPONENTS
Section E6B
Diodes
What is the most useful characteristic of a Zener diode?
  • A constant current drop under conditions of varying voltage
  • Correct Answer
    A constant voltage drop under conditions of varying current
  • A negative resistance region
  • An internal capacitance that varies with the applied voltage

A Zener Diode is a diode that allows voltage to flow from anode to cathode under normal circumstances, but also allows voltage to reverse direction (called the Zener effect) when it reaches its Zener Voltage. They are commonly used in voltage reference circuits.

The voltage drop remains relatively constant under varying current.

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What is an important characteristic of a Schottky diode as compared to an ordinary silicon diode when used as a power supply rectifier?
  • Much higher reverse voltage breakdown
  • Controlled reverse avalanche voltage
  • Enhanced carrier retention time
  • Correct Answer
    Less forward voltage drop

The Schottky diode also known as hot carrier diode, is a semiconductor diode with a low forward voltage drop and a very fast switching action. The cat's-whisker detectors used in the early days of wireless and metal rectifiers used in early power applications can be considered primitive Schottky diodes.

When forward current flows through a solid-state diode, there is a small voltage drop across its terminals. A silicon diode has a typical voltage drop of 0.6–0.7 V, while a Schottky diode has a voltage drop of 0.15–0.45 V. This lower voltage drop can be used to give higher switching speeds and better system efficiency.

The Schottky diode is often used as a voltage limiter (aka clamp or bypass diode), in reverse bias.

-devdev

See Schottky_diode on Wikipedia.

When something is Schott (shot), it typically will drop

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What special type of diode is capable of both amplification and oscillation?
  • Point contact
  • Zener
  • Correct Answer
    Tunnel
  • Junction

Tunnel Diodes are used in frequency converters and detectors. They have negative differential resistance in part of their operating range, and therefore are also used as oscillators, amplifiers, and in switching circuits using hysteresis.

http://en.wikipedia.org/wiki/Tunnel_diode

Hint think of shouting down a long underground tunnel, your voice will be amplified and echo(oscillate) W9ECO

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What type of semiconductor device is designed for use as a voltage-controlled capacitor?
  • Correct Answer
    Varactor diode
  • Tunnel diode
  • Silicon-controlled rectifier
  • Zener diode

In electronics, the following:

  • a varicap diode
  • varactor diode
  • variable capacitance diode
  • variable reactance diode
  • tuning diode

are types of diode whose capacitance varies as a function of the voltage applied across its terminals.

http://en.wikipedia.org/wiki/Varicap

Hint: "V" in voltage, "V" in varactor diode.

Also think variable capacitor diode.

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What characteristic of a PIN diode makes it useful as an RF switch or attenuator?
  • Extremely high reverse breakdown voltage
  • Ability to dissipate large amounts of power
  • Reverse bias controls its forward voltage drop
  • Correct Answer
    A large region of intrinsic material

The I in PIN means intrinsic!

Wikipedia: A PIN diode is a diode with a wide, undoped intrinsic semiconductor region between a p-type semiconductor and an n-type semiconductor region. The p-type and n-type regions are typically heavily doped because they are used for ohmic contacts.

The wide intrinsic region is in contrast to an ordinary PN diode. The wide intrinsic region makes the PIN diode an inferior rectifier (one typical function of a diode), but it makes the PIN diode suitable for attenuators, fast switches, photodetectors, and high voltage power electronics applications because it has low junction capacitance.

Test Hint: PIN - 3 letters. Answer - 3 words

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Which of the following is a common use of a hot-carrier diode?
  • As balanced mixers in FM generation
  • As a variable capacitance in an automatic frequency control circuit
  • As a constant voltage reference in a power supply
  • Correct Answer
    As a VHF/UHF mixer or detector

A hot carrier diode is also known as a Schottky Barrier Diode. It's a fast switching diode (due to low capacitance) with a low forward voltage drop. Their fast switching makes them effective as a mixer or detector at VHF/UHF frequencies. -- david_abraham

Note also that Schottky Barrier Diodes are also commonly used in power supply circuits because the lower forward voltage drop reduces power dissipation and improves efficiency. However, they don't support high current loads.

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What is the failure mechanism when a junction diode fails due to excessive current?
  • Excessive inverse voltage
  • Correct Answer
    Excessive junction temperature
  • Insufficient forward voltage
  • Charge carrier depletion

Some of the power that flows through a junction diode is dissipated in the form of heat. If a diode becomes too hot it will be damaged or destroyed.

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Which of the following describes a type of semiconductor diode?
  • Correct Answer
    Metal-semiconductor junction
  • Electrolytic rectifier
  • CMOS-field effect
  • Thermionic emission diode

A hot-carrier diode (Schottky diode) is used as a VHF/UHF mixer or detector. In construction, a metal–semiconductor junction is formed between a metal and a semiconductor, creating a Schottky barrier (instead of a semiconductor–semiconductor junction as in conventional diodes).

https://en.wikipedia.org/wiki/Schottky_diode

Hint: "Semiconductor" is in the answer. Think a barrier made out of metal!! WP4AES

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What is a common use for point contact diodes?
  • As a constant current source
  • As a constant voltage source
  • Correct Answer
    As an RF detector
  • As a high voltage rectifier

Point contact diodes are derived from crystal detectors and are good high frequency detectors. The key word is "detector"

Complete explanation here: https://electronicscoach.com/point-contact-diode.html

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In Figure E6-3, what is the schematic symbol for a light-emitting diode?
  • 1
  • Correct Answer
    5
  • 6
  • 7

The arrows coming off the diode represent the emission of photons. So symbol 5 is a diode that emits photons-- also known as a light emitting diode.

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What is used to control the attenuation of RF signals by a PIN diode?
  • Correct Answer
    Forward DC bias current
  • A sub-harmonic pump signal
  • Reverse voltage larger than the RF signal
  • Capacitance of an RF coupling capacitor

A PIN diode is a semiconductor device that operates as a variable resistor at RF and microwave frequencies. One common use for PIN diodes is as an RF switch. (E6B12)The characteristic of a PIN diode that makes it useful as an RF switch or attenuator is a large region of intrinsic material. (E6B05) The forward DC bias current is used to control the attenuation of RF signals by a PIN diode. (E6B11)

Remember that you can have both an AC and a DC component of current flow in a circuit. In this case, a DC component is used to control the AC component.

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What is one common use for PIN diodes?
  • As a constant current source
  • As a constant voltage source
  • Correct Answer
    As an RF switch
  • As a high voltage rectifier

Under zero or reverse bias, a PIN diode has a low capacitance. The low capacitance will not pass much of an RF signal. Under a forward bias of 1 mA, a typical PIN diode will have an RF resistance of about 1 ohm, making it a good RF conductor. Consequently, the PIN diode makes a good RF switch.

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What type of bias is required for an LED to emit light?
  • Reverse bias
  • Correct Answer
    Forward bias
  • Zero bias
  • Inductive bias

Before a light emitting diode can “emit” any form of light it needs a current to flow through it, as it is a current dependent device with their light output intensity being directly proportional to the forward current flowing through the LED.

See ElectronicsTutorials

In electronics, bias is a steady voltage, magnetic field, or other factor applied to an electronic system or device to cause it to operate over a predetermined range.*

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