diode
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Diode
Electronic CircuitsElectronic Circuits
CHO, Yong HeuiCHO, Yong Heui
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1. Ideal diode
Nonlinear device
No voltage drop External circuits
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Output Waveform
Equivalent Circuits Waveform of
VD
1. Ideal diode
Rectifier: ideal diode
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Logic definition: 0 V [0], 5 V [1]
Y = A · B · CY = A + B + C
1. Ideal diode
Logic circuits
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i = Is(ev/nVT – 1)
IS(T) : reverse-biased saturation current
depends on Temp. and junction area
≈ 10-15 (doubles at every 5 ºC)
VT = kT/q
V2 – V1 = 2.3nVT·log(I2/I1)
2.3VT is theoretical threshold swing : 60 mV
2. Junction diode
Forward bias
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Reverse-bias / Breakdown regions
i = Is(ev/nVT – 1) i ≈ Is when v is negative and more than a few VT
Reverse current : doubles for every 10 ºC
Zener breakdown and avalanche breakdown
Temperature dependence
2. Junction diode
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The exponential model:
ID = Isev/nVT
ID = (VDD – VD) / R
ID = Isev/nVT
Graphical Analysis
3. Modeling
Exponential model
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iD = 0, vD ≤ VD0
iD = (vD - VD0) / rD , vD ≥ VD0
3. Modeling
Piecewise linear model
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iD = 0, vD ≤ VD
iD = undefined , vD ≥ VD
3. Modeling
Constant voltage model
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rD = nVT / ID : small-signal resistance
id = IDvd/nVT = vd / rD
ID = Isev/nVT
vD(t) = VD + vd(t)
iD(t) ≈ ID(1 + vd/nVT) , vd/nVT ≪ 1
iD(t) = ID + IDvd/nVT = ID + id
3. Modeling
Small signal model
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At Bias point, ΔV = ΔI ·rZ
rZ : dynamic resistance
Almost linear i-v characteristics
VZ = VZ0 + rZ·IZ
IZK : minimum current for the operation of Zener diode
4. Zener diode
Breakdown region
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Shunt Regulator: VZ = 6.8V, IZ = 5 mA, rZ = 20Ω, and IZK = 0.2 mA
4. Zener diode
Shunt regulator
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Shunt Regulator: VZ = 6.8V, IZ = 5 mA, rZ = 20Ω, and IZK = 0.2 mA
4. Zener diode
Shunt regulator
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Shunt Regulator: VZ = 6.8V, IZ = 5 mA, rZ = 20Ω, and IZK = 0.2 mA
4. Zener diode
Shunt regulator
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V1 / V2 = N1 / N2
5. Rectifier
DC power supply
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vO = 0, vS < VD0
R
R + rD
vS - VD0
R
R + rD
vO =
vS ≥ VD0
≈ vS – VD0 , for rD ≪ R
5. Rectifier
Half-wave rectifier
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PIV = 2VS – VD0
5. Rectifier
Full-wave rectifier
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vD3(reverse) = vO + vD2(forward)
PIV = Vs -2VD + VD = Vs - VD
5. Rectifier
Bridge rectifier
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Ideal case
5. Rectifier
Peak detector
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t1 < t < t2
Vr = VP – vO(T-ΔT) =
iDmax = IL(1 + 2π√2Vp/Vr)iDav = IL(1 + π√2Vp/Vr)
5. Rectifier
Peak rectifier
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Precision half-wave rectifier
5. Rectifier
Rectifier with RC load
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6. Limiter
Limiting circuits
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6. Limiter
Clamping circuits
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6. Limiter
Voltage doubler