BJT

Question 1

Polarização BJT

Answer 1

-When a positive voltage is applied to the base (with respect to the emitter)
– The base region is light doped and very thin
– Because it is lightly doped, the current produced is mainly due to electrons
flowing from the emitter to the base
– Because the base region is thin, most of the electrons entering the base get swept
across the base-collector junction into the collector
– This produces a collector current that is much larger than the base current – this
gives current amplification
– EB forward-bias lower EB potential barrier –
electron injection in B and holes in E
– Electrons in B (minority carriers, InE): some
recombine with holes, others diffuse through B and
reach C

Question 2

Ic

Answer 2

• IC is independent of VCB as long as VCB is a reverse bias.
• IC is determined by the rate of electron injection from the emitter into the base, i.e., determined by VBE

Question 3

Zona de saturação

Answer 3

• both BE and BC forward biased
• region near to the origin is the saturation region (B saturated of minority carriers injected from E and C)
  – Corrente no coletor controlada pelo circuito coletor

Question 4

Zona ativa/linear

Answer 4

Corrente do coletor proporcional à corrente na base

Question 5

Breakdown

Answer 5

Ocorre multiplicação da corrente do coletor por avalanche.

Question 6

Early effect

Answer 6

-Com o aumento da polarização inversa entre a base e o coletor, a width da região de depleção entre o coletor e a base aumenta e o comprimento da base diminui.
-Early effect: When output characteristics are extrapolated back to point of zero iC, curves intersect (approximately) at a common point vCE = -VA
-Increasing VCE, the base-collector
depletion region widens and the neutral base width decreases – IC
increases