fundamentals of engineering supplied-reference handbook - Ventech!
fundamentals of engineering supplied-reference handbook - Ventech!
fundamentals of engineering supplied-reference handbook - Ventech!
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Device and Schematic<br />
Symbol<br />
(Junction Diode)<br />
(Zener Diode)<br />
Schematic Symbol<br />
Ideal I – V<br />
Relationship<br />
DIODES<br />
Piecewise-Linear<br />
Approximation <strong>of</strong> The<br />
I – V Relationship<br />
183<br />
ELECTRICAL AND COMPUTER ENGINEERING (continued)<br />
Mathematical<br />
I – V Relationship<br />
Shockley Equation<br />
( vD<br />
ηVT )<br />
i D ≈ I s[<br />
e −1]<br />
where<br />
Is = saturation current<br />
η = emission coefficient, typically 1 for Si<br />
kT<br />
VT = thermal voltage =<br />
q<br />
Same as above.<br />
NPN Bipolar Junction Transistor (BJT)<br />
Mathematical<br />
Large-Signal (DC) Low-Frequency Small-Signal (AC)<br />
Relationships<br />
Equivalent Circuit<br />
Equivalent Circuit<br />
iE = iB + iC<br />
Active Region:<br />
Low Frequency:<br />
iC = βiB<br />
iC = αiE<br />
α = β/(β + 1)<br />
base emitter<br />
biased; base<br />
reverse biased<br />
junction<br />
collector<br />
forward gm ≈ ICQ/VT<br />
junction<br />
rπ ≈ β/gm,<br />
( VBE<br />
VT<br />
)<br />
iC ≈ IS e<br />
⎡∂vCE<br />
⎤<br />
ro = ⎢ ⎥<br />
⎣ ∂ic<br />
⎦<br />
VA<br />
≈<br />
ICQ<br />
IS = emitter saturation<br />
current<br />
VT = thermal voltage<br />
Note: These relationships are<br />
valid in the active mode <strong>of</strong><br />
operation. Saturation Region:<br />
both junctions forward biased<br />
Same as for NPN with current<br />
directions and voltage polarities<br />
reversed.<br />
7<br />
Cut<strong>of</strong>f Region:<br />
both junctions reversed biased<br />
Same as NPN with current<br />
directions and voltage polarities<br />
reversed<br />
7<br />
where<br />
Q<br />
point<br />
IC Q = dc collector current at the<br />
Qpoint<br />
VA = Early voltage<br />
Same as for NPN.
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