Diode

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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