diode/ power supply

Conductors have

A) loosely bound valance electrons and low resistance

which of the following is not a conductor

C. Silicon

how many Valence electrons do semiconductors have?

A. 4

At room temperature pure silicon crystals conduct

A. very poorly

As room temperature increases, the resistance of a conductor will

A. increase

As temperature increases, the resistance of a semiconductor will

B. decrease

If a silicon crystal is doped with a material having five valence electrons

C. A N-type semiconductor is formed

If a silicon crystal is doped with a material having three valence electrons

B. P-type semiconductor is formed

the direction of electron current is

A. Neg to Pos

Doping a semiconductor

C. decreases its resistance

In a PN junction diode, the depletion region is formed by

A. electrons crossing the junction and filling holes

The depletion region of a PN junction diode acts as

B. an insulator

With no external bias applied, the depletion region is limited or balanced by

C. the barrier potential

In a PN junction diode, FWD can

• Force the majority carriers

• collapse the depletion region

• cause conduction from cathode to anode

Excessive reverse bias may cause a silicon diode to

A. avalanche

In order for a diode to be FWD biased

• The P-type material must be positive with respect to the N-type material

• the anode must be positive with respect to the cathode

• the electron current must be flowing against the arrow on the schematic symbol

at high temperatures, the FWD voltage drop across a diode can be expected to

C. Be less than it is at low temperature

An ohmmeter is connected across diode both ways, and rather low resistance reading is obtained both times, the diode is

Shorted

The band on a diode identifies the

cathode

Rectifier diodes are used to

C. change AC into DC

In rectifier circuits, the positive end of the load is the one that connects

B. the cathode of the rectifier

If the diode in a half-wave rectifier circuit is reversed, the voltage across the load will

B-reverse in polarity

The effectiveness of a capacitor filter is determined by

-The size of the capacitor

-the amount of current

-the ripple frequency

Full wave rectifier are often preferred over half-wave rectifier because

-can deliver more power and are easier to filter

if the load should be disconnected from the regulator, the power dissipation in R1 will

A- remain the same

If the load should be disconnected from the regulator, the power dissipiation in D1 will

C-Increase

Band Gap

The energy that needs to be applied to an electron in order for it to move from the valence electron to the conduction band

Fermi level

the energy level half way between the valence and conduction bands

if band gap overlaps

good conductor

If band gap is far apart

Good insulator

Doping

adding impurities to the silicon crystal lattice to increase the number of carriers