M04 B2

What are the most important elements that are used for semiconductors?

silicon and germanium

Z-Diodes are ?

silicon diodes with a specifically defined steep breakdown in the reverse biased direction.

When the PN junction is formed, what happens to the N region?

, the N region loses free electrons as they diffuse across the junction, creating a layer of positive charges near the junction.

The semi-conductor is divided into two types:

- Intrinsic Semi-conductor - Extrinsic Semi-conductor

For germanium diodes the threshold voltage is approximately

0.3 Volts

The threshold voltage of a silicon diode

0.7 volts are required to break down the depletion zone. A silicon diode will only allow a current to flow completely through the junction at voltages above this level.

With the negative pole at the n−area and the positive pole at the p−area, the depletion area breaks down and the semiconductor diode will let the current pass across the junction. This called?

Forward Bias

What will a serviceable diode show on the multimeter when test in forward bias and reverse bias ?

Forward Bias: 0.7 volts Reverse Bias: internal Voltage

What are the majority and minority carries of a N-region?

The N region has many free electrons (Majority Carriers) from the impurity atoms and only a few thermally generated holes (Minority Carriers).

What are the majority and minority carries of a P-region?

The P region has many holes (Majority Carries) from the impurity atoms and only a few thermally generated free electrons (Minority Carries).

What do you need in order to produce direct−current voltage?

a charging capacitor CL is connected in parallel to RL.

A diode based clipper in general consists of ?

a diode, a resistor and a voltage source that provides a reference voltage.

The filter circuit is ?

a frequency dependent voltage divider

The intrinsic conductivity of a semiconductor depends on?

a large degree on temperature. The higher the temperature the higher the intrinsic conductivity will be in both forward and reverse direction of a semiconductor.

What happens if a Pentavalent impurity, having five valence electrons (Phosphor) is added to a pure semiconductor

a large number of free electrons will exist and classified as N-type semiconductor.

What happens if If a Trivalent impurity having three valence electrons (Boron) is added

a large number of holes will exist in the semiconductor and classified as P-type semiconductor.

A diode is a

device that allows current to flow in one direction only. (it a device that has two electrodes).

In LDR when light is directed onto a surface made of a semiconductor material, the resistance will ?

diminishes because light energy releases electrons from their orbital bonds.

A simple clamper consists of a

diode, a capacitor and a resistor.

LDR can be used in circuits of

direct and alternating current

Multilayered semiconductors are

electrical components that consist of various layers which have been doped in different ways.

The Delon Circuit reminds one of a two-way rectification, but the two half-cycles are ?

not sent to the load together, instead capacitors are charged and the total of the two capacitor voltages is the new output voltage. The two half waves are added.

A thyristor consists

of 4 semiconductor zones with an anode terminal and a cathode terminal. There are 3 PN junctions, which are denoted as junctions I, II and III.

What happens when a single−wave rectifier without a charging capacitor is used,

only the respective half−waves of the alternating current affects the load resistance RL. (either only positive or only negative).

A full wave rectifier is defined as a

rectifier that converts the complete cycle of alternating current into pulsating DC.

Z−diodes are mainly used to ?

regulate electrical voltage.

A diode will show a very high resistance (or open circuit) if wired in the

reverse bias direction

Varicaps are used in ?

reverse−biased direction for regulating resonant circuits.

Photodiodes are?

semiconductors with a P-N-junction that is exposed to light.

The Cascade Circuit is a series connection of ?

several Villard Circuits and works according to their principle. This circuit is often used in TV sets, computer monitors, and oscilloscopes.

If the voltages to be blocked by the diodes exceeds the maximum permissible reverse voltage of a diode

several diodes may be connected in series.

If it has failed in the short circuit condition it will show

show zero (or nearly zero) in both directions.

The breakdown voltage Z-diodes is dependent on

temperature

If a charging capacitor is used in a full wave rectifier, as similar situation arises as in the case of a single−wave rectifier with the exception

that the hum voltage at the same load resistance is lower while at the same time, it is two times the frequency of the power grid.

The pure form of a semi-conductor is known as

the Intrinsic Semi-Conductor

Cascades are often used for

the creation of high voltage necessary for cathode ray tubes, Geiger-Müller counters, or igniter boxes.

A variable capacitance diode or Varicap provides ?

the extremely thin layer−like junction of a silicon diode with capacitance.

Connecting diodes in parallel is possible in general but has several limitations. Such a parallel connection is used when ?

the forward current exceeds the maximum forward current of an individual diode.

The quality of the filtering is expressed by?

the levelling factor G or filtering factor S

In a diode clippers the voltage level and polarity of the reference voltage provide?

the maximum output voltage of this clipper.

The resistance of a VDR or Varistor decreases when?

the voltage is increasing

The resistance level of a varistor depends on ?

the voltage that is applied

What is a Transformer Rectifier Unit

these units transform AC Power to DC Power with a low voltage.

In photodiode what happens if the junction is in the dark ?

they block the current like every other diode.

What is the purpose of adding impurities in a semiconductor?

to increase the number of free electrons or holes to make it conductive under controlled conditions.

If information is transmitted via radio or if a circuit contains capacitors the DC voltage levels will get lost. A clamper is used

to restore such DC voltages.

Delon circuit is also called ?

voltage doubler

What happens when the load resistance RL of the rectifier circuit, is pulsating direct−current?

voltage is produced

A bridge circuit is a full−wave rectifier circuit

where the disadvantage of a normal full−wave rectification circuit, the tapped transformer, disappears. It is also called WYE Rectifier.

We can use a single wave rectifier in two ways

with or without a charging capacitor

If a charging capacitor is used the rectifier has a capacitive load, this changes the conditions so that the diode is

not conductive during the entire positive half−wave but only opens when the transformer voltage UTr is greater than voltage U.

Why are cascades more advantageous than high voltage transformers?

Because of the low current consumption of these devices

When a Multimeter is set to the diode test position it will supply a voltage sufficient to forward and reverse bias the diode. This voltage will be approximately

2.5−3.5 volts (Internal Voltage of the Multimeter).

What happens if a piece of intrinsic silicon is doped and a n-type , P-type is created?

A PN junction forms at the boundary between the two regions and a diode is created.

What is a single wave rectifier (half wave) ?

A half-wave rectifier converts an AC signal to DC by passing either the negative or positive half-cycle of the waveform and blocking the other.

The Polarity of a VDR

Does not matter

The polarity of an LDR

Does not matter

The process by which an impurity is added to a Semi-Conductor is known as?

Doping

Disadvantage of LC-Filtering

Expensive inductor

A semiconductor to which an impurity is added to make it conductive is known as?

Extrinsic Semi-Conductor (Doped Semi-conductor)

Schottky diodes contain metal semiconductor junctions that have quite the same properties as ?

P-N junctions. As an example aluminum and N-doped silicon are joined.

Anode

Positive electrode

If the positive pole of a voltage source is at the n−area and the negative pole is at the p−area, a depletion zone forms at the junction (because there are no free electrons or empty spaces for electrons) and the semiconductor blocks the charge. This is called ?

Reverse Bias

LEDs are used in ?

Forward Bias

What is the disadvantage of varicaps ? and how can they be diminished

At a high amplitude Ua, distortions will occur, This disadvantage can be diminished if two Varicaps are connected in series.

Threshold voltage

If no voltage is applied, a small depletion area forms which must be removed before current can flow in the forward−biased direction. Semiconductor diodes only allow current to pass completely through them if the voltage is above the threshold voltage.

Diodes can also be used to short-circuit the back-emf that occurs when switching off relays.

If the relay is supplied with DC the diode will operate in reverse direction. If the power supply is switched off, the inductivity will generate the back-emf. This voltage will operate the diode in forward direction. Thus, other components will not be affected by the back-emf.

What is the peak inverse voltage?

If the voltage in the direction of the depletion zone is too high, a depletion zone breakthrough occurs and, in most cases, the semiconductor diode will be destroyed. The manufacturer always specifies the maximum permissible reverse voltage. In silicon diodes this can up to 5kV. In germanium diodes it must be less than 200 volts.

What are semiconductors?

Semiconductors are elements or compounds which, under normal conditions, contain relatively few free (moving) electrons. On a scale of electrical conductivity, they are between the conductors and the insulators. A semi-conductor has 4 electrons in the valence shell.

A diode has two parts (2 layers)

N-type semi conductor P-type semi conductor

Cathode

Negative electrode

Light Dependent Resistors are?

No diodes, but they are made of semiconductor material

Varistors are ?

No diodes, but they are made of semiconductor material.

Villard Circuit is based on ?

One-way rectifier

Advantage of LC-Filtering

Only small loss of DC: RLS x IL.

In a single wave what happens to humming voltage?

The alternating current which overlays the average direct current, the so−called humming voltage, is the same frequency as that of the power grid.

Maximum Forward Current

The current in the forward−biased direction must not exceed the limits given by the manufacturer. Every manufacturer specifies the maximum forward−biased current for each diode type. This value depends on the cooling system used with the diode. DO NOT exceed the maximum forward current level. This will destroy semiconductor diodes.

What is the polarity of a photodiode ?

They are always connected in reverse direction.

Why do we use a protective resistor in a single wave circuit ?

a protective resistor is often incorporated in front of diodes in order to limit the incoming current.

What happens to the semiconductor when the temp. reaches 0 degrees kelvin ?

a semiconductor is a non−conductor. When the temperature increases, an electron can be thrown off its atom and a positive charge remains which is called a defect electron or an electron hole.

The usage of LDR

are especially useful (in appropriate circuit configurations) for measuring low levels of illumination

Rectifier Diodes

are primarily used for electrical power supply devices. They are used to construct rectifier circuits for small power outputs.

A disadvantage of RC filtering is?

at RS, direct current voltage with the magnitude of RS x lL is lost.

In photodiode what happens if the junction is illuminated ?

charges will be created within the depletion area. The diode becomes conductive.

An intrinsic conductor is capable to

conduct a little current even at room temp. but it is not useful for the preparation of various electronic devices.

LED stands for light emitting diodes. As the name states, they are semiconductor diodes that

emit light. The colour of the light depends on the semiconductor material that is used.

Thyristors are

fast electronic switches (up to 10 kHz). They are diodes with a control terminals or gates.

A DIAC is a

five−layer electrical component which results when 2 thyristors have an antiparallel connection or when a three−layer component has layers which are arranged as P−N−P.

A diode will show a very low resistance when wired in the

forward bias direction

Thyristors are constructed in

four alternating layers, P−N−P−N, so that three P−N junctions form between the layers.

In the case of full−wave rectifiers without a charging capacitor, both half−waves of the alternating current

have an effect on the workload, but in the same direction.

If the diode is faulty in the open circuit condition then the reading will be

high resistance (or open circuit) in both directions (Switch Positions).

Delon Circuit are used in airplanes by?

igniter box

Where are rectifiers used ?

in brushless generators

Schottky diodes are used in

integrated circuits

If a diode has failed open circuit, it will show

internal voltage of the meter in both forward and reverse bias.

Clippers are used to ?

limit voltages to a certain level. So a maximum amplitude is given for the positive or negative voltage. The output voltage then can never exceed the given limits.

If it has failed in the short circuit condition (less likely) then it will show

low resistance in both directions (Switch Positions)

Microdiodes are

mainly used in communication technology

High power diodes have

maximum forward−biased currents of approximately 10 to 1000 amperes. They are used in rectifier circuits for large power outputs.