1 Semiconductor Diodes
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Transcript of 1 Semiconductor Diodes
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1.0. Semiconductor Diodes 1 of 27 1.2 Ideal Diode
ID
VD
ID
Open Circuit
Short CircuitVD
+ -
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1.0. Semiconductor Diodes 2 of 27 1.3 Semiconductor Materials Conductor Insulator Semiconductor
R = (Resistivity, ρ ohm-cm) * (Length, L cm) / (Area, cm2) = RA/L R = (50,000 ohm-cm)(4 cm)/(2cm x 4cm) = 25,000 ohms Resistivity of a semiconductor decreases as temperature increases.
ure coefficient. Negative temperat
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1.0. Semiconductor Diodes 3 of 27 Ge and Si single-crystal structure
Atomic structure: (a) germanium; (b) silicon.
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1.0. Semiconductor Diodes 4 of 27 Energy Levels
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1.0. Semiconductor Diodes 5 of 27
W = QV joules Q = 1.6 x 10-19 coulomb (1 electron worth of charge)(1V) = 1.6 x 10-19 Joule (1.6 x 10-19 coulomb)(1V) = 1.6 x 10-19 Joule 3 electrons and 2 volts 3 electrons have a charge = 4.8(10-19) comlomb 4.8(10-19 coulomb)(2 volts) = 9.6(10-19) Joule or 6eV
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1.0. Semiconductor Diodes 6 of 27 1.5 Extrinsic Materials – doped
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1.0. Semiconductor Diodes 7 of 27 (a) n-type material; (b) p-type material.
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1.0. Semiconductor Diodes 8 of 27 1.6 Semiconductor Diode p-n junction with no external bias
Carriers combine, resulting in depletion region
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1.0. Semiconductor Diodes 9 of 27 Reverse-biased p-n junction.
electrons holes
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1.0. Semiconductor Diodes 10 of 27 Forward-biased p-n junction.
electronsholes
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1.0. Semiconductor Diodes 11 of 27 Silicon semiconductor diode characteristics.
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1.0. Semiconductor Diodes 12 of 27 ID = Is(ekV/T – 1) k constant, 11,600/η η= 1 for Ge and 2 for Si V diode forward voltage T temperature in Kelvin, 273o + temp in centigrade Example: Si, voltage = 0.7, k=5800, Is = -25nA
k 5800
K 273
TA 20
TK K TA
Is 25 10 9.
VD 0.7
ID Is ek
VDTK.
1. .02605004764852208305
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1.0. Semiconductor Diodes 13 of 27
Peak Inverse Voltage - usually >50 volts
Tempers for every10o C increase in temperr every10o C increase in temperature
V_V1
-6.0V -5.0V -4.0V -3.0V -2.0V -1.0V -0.0V 1.0VI(D1)
-20mA
-10mA
0A
10mA
20mA
Zener region VT = 0.7 Si
ature effects
Current double ature VT decreases 2mv for every1o C VT decreases 2mv for every1o C
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1.0. Semiconductor Diodes 14 of 27 1.8 Resistance Levels Diode I-V characteristic
DC Resistance
RD = VD / ID
V_V1
0V 0.5V 1.0V 1.5V 2.0V 2.5V 3.0V 3.5V 4.0V 4.5V 5.0VI(D1)
0A
10mA
20mA
30mA
Q-point Quiescent point Operating point
1V/15mA = 0.0667*1000 66.7
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1.0. Semiconductor Diodes 15 of 27 AC or Dynamic Resistance
RD = ∆Vd / ∆Id
V_V1
0V 0.5V 1.0V 1.5V 2.0V 2.5V 3.0V 3.5V 4.0V 4.5V 5.0VI(D1)
0A
10mA
20mA
30mA
Q-point Quiescent point Operating point
for example at 25mA in Fig. 1.34 on page 22, RD = ∆Vd / ∆Id = (0.8V – 0.78V)/(30mA – 20mA) = 2 ohms
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1.0. Semiconductor Diodes 16 of 27 Using calculus we get approx,
1/rD = dI/dV = d/dV (Is(ekV/T – 1) = Is (k/T) ekV/T
= (k/T) Is ekV/T
which is almost
1/rD = kID / T at room temp 25oC rd = 26mv / ID at 15mA, rd = 26mv / 15mA 1.733 ohms
rd’ = (26mv / ID) + rB , add diode body resistance
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1.0. Semiconductor Diodes 17 of 27 Average AC resistance
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1.0. Semiconductor Diodes 18 of 27 1.9 Diode Equivalent Circuits Piecewise-Linear Equivalent Circuit
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1.0. Semiconductor Diodes 19 of 27
deal diode and its characteristics.
Simplified equivalent circuit for the silicon semiconductor diode.
I
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1.0. Semiconductor Diodes 20 of 27 1.10 Diode Specification Sheets
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1.0. Semiconductor Diodes 21 of 27 1.11 Transition and Diffusion Capacitance Reverse bias – capacitance of depletion region. CT Forward bias – excess charge injected into regions just outside the depletion region, CD.
1.12 Reverse Recovery Time Diffusion capacitance (charge stored). Reversing the bias sweeps the stored charge out.
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1.0. Semiconductor Diodes 22 of 27 FIGURE 1-42 Transition and diffusion capacitance versus applied bias for a silicon diode.
At V = 0.25 the CD = 9pF At V = -15 the CT = 1pF
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1.0. Semiconductor Diodes 23 of 27 1.13 Semiconductor Diode Notation 1.14 Diode Testing 1.15 Zener Diodes Conduction direction: (a) Zener diode; (b) semiconductor diode.
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1.0. Semiconductor Diodes 24 of 27
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1.0. Semiconductor Diodes 25 of 27 1.16 Light Emitting Diodes
(a) Process of electroluminescence in the LED; (b) graphic symbol.
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1.0. Semiconductor Diodes 26 of 27
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1.0. Semiconductor Diodes 27 of 27 1.17 Diode Arrays – Integrated Circuits 1.18 Summary 1.19 Computer Analysis