Module 2.2: Semiconductor Diode

Average AC Resistance

resistance associated with the device when a large signal is used as an input to produce a broad a swing; to determine a value-straight line is drawn between 2 intersections established by the maximum and minimum values of input values

Static Resistance or DC

resistance of the diode at the quiescent point; result in an operating diode on the characteristic curve that will not change in time the higher the current through a diode, the lower is the dc resistance level

simplified diode model

second approximation; the diode in forward biased-has some threshold voltage but with no resistance; reverse biased- it is an open circuit

bias

use o f a dc voltage to establish a certain operating conditions for an electronic device

Breakdown voltage

maximum voltage that can be handled by the junction diode; also known as peak reverse voltage or peak inverse voltage

Ideal diode model

1st approximation; if the turn on voltage is very small compared to other voltages in the circuit and diodes resistance is negligible compare to other; representing it as a switch

400V

PIV of Germanium

1000v

PIV of Si

Barrier Potential

The amount of energy required to produce full conduction across the pn junction in forward bias.

pn junction diode

a microelectronics device composed of adjacent layers of p-type and n-type semiconductors that serves to pass current in one direction while (essentially) blocking current in the opposite direction

Diode Equivalent Model

aka Diode equivalent circuit; combination of circuit element that best represents the actual characteristics of a semi conductor under a specific operating condition

transition region Capacitance

aka depletion region capacitance; capacitance in reverse bias condition

diffusion capacitance

aka storage capacitance; capacitance in forward bias region and always greater in value than depletion region capacitance

Dynamic Resistance or AC

application of an ac voltage will move the instantaneous operating point up and down a particular region since the value of ID and VD will also vary; resistance changes as you move the V-I curve; resistance of a forward bias diode is not constant over the entire curve

diode capacitance

electronic devices are inherently sensitive to a very high frequencies; 2 capacitive effects

PN Junction Diode

formed by doping one-half of intrinsic Si or Ge with a p-type dopants and the other half with an n-type dominant

PN Junction

formed when an n-type and a p-type materials are brought together; formed at the boundary between 2 regions

reverse current will drastically change

if the external reverse bias is increased to a value called breakdown voltage

high reverse bias voltage

imparts energy to free minority electrons; collide with atoms with enough energy to knock valence electrons out of orbit and into the conduction band

avalanche

multiplication of conduction electrons; results in a very high reverse current and can damage the PN Junction structure because of the excessive heat dissipation

biasing pn junction

no electrons move through the PN Junction at equilibrium and since the flow of electrons is electrical current, there is no electrical current through the PN junction

Depletion Region

region near the PN Junction is depleted of change carriers (both electrons and holes) due to diffusion across the junction

true

silicon diodes have higher PIV and current ratings than germanium

100 C

temperature range for Ge

200 C

temperature range for Si

conduction electrons

these newly conducted free electrons are also high in energy and repeat the process

piecewise linear diode model

third approximation; diode in forward bias has some threshold voltage and a bulk resistance; reverse biased- an open circuit

knee voltage

voltage wherein the sudden increase in current starts

forward bias

when the negative terminal of the AC source is connected to the N-end and the positive terminal to the P-end, electrons and holes flow toward each other, reducing the barrier voltage, allowing current to flow across the junction and the external circuit.

reverse bias

when the positive terminal of the AC source is connected to the N-end and the negative terminal to the P-end, electrons and holes move away from each other, increasing the barrier voltage and preventing current across the junction; making the depletion region wider expecting no current flow