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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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Which characteristic of a Schottky diode makes it a better choice than a silicon junction diode for use as a power supply rectifier?

  • Much higher reverse voltage breakdown
  • More constant reverse avalanche voltage
  • Longer carrier retention time
  • Correct Answer
    Lower 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.

See Schottky_diode on Wikipedia.

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

Hint: The wrong answers all go in the same direction: Higher, More and Longer.

The correct answer goes opposite with 'Less'.

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What property of an LED's semiconductor material determines its forward voltage drop?

  • Intrinsic resistance
  • Correct Answer
    Band gap
  • Junction capacitance
  • Junction depth
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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.

Logical hint: The word varactor is made of two main parts: "v" and "actor." I think of it as being voltage reactor. Reactor means that it reacts to changes, in this case changes in voltage.

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What characteristic of a PIN diode makes it useful as an RF switch?

  • Extremely high reverse breakdown voltage
  • Ability to dissipate large amounts of power
  • Reverse bias controls its forward voltage drop
  • Correct Answer
    Low junction capacitance

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 Schottky diode?

  • In oscillator circuits as the negative resistance element
  • As a variable capacitance in an automatic frequency control circuit
  • In power supplies as a constant voltage reference
  • Correct Answer
    As a VHF/UHF mixer or detector
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What causes a junction diode to fail from 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.

When a component is damaged, we may say "it let the smoke out." Think "smoke," think "fire." Think "fire," think "hot."

silly hint: Both the question and the correct answer contain the word junction

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Which of the following is a Schottky barrier diode?

  • Correct Answer
    Metal-semiconductor junction
  • Electrolytic rectifier
  • PIN junction
  • 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!!

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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

Hint: to make "Contact" between two "Points" you'll need a "Detector"

Hint: "Diode" and "Detector" both start with D.

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In Figure E6-2, which is the schematic symbol for a Schottky diode?

  • 1
  • Correct Answer
    6
  • 2
  • 3
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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 variable RF reference voltage
  • 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.

Hint: Think of "control the current" (only answer that has "current" in it.

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