pn juction characteristics

8/12/2019 pn juction characteristics

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Graphical

PN-Junction Diode V-I Characteristic

Reverse

breakdown

Forward Bias Region

Reverse Bias Region


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Mathematical Approximation

D

T

V

V

D sI = I (e -1)


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Ideal PN Junction Diode V-I Characteristic

Forward BiasShort Circuit

Reverse BiasOpen Circuit


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Diode Reverse Recovery Time

tais the time to remove the charge stored in the

depletion region of the junction

tbis the time to remove the charge stored in the bulk

semiconductor material


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Reverse Recovery Characteristics

Soft Recovery

Reverse recovery time = trr= ta+tb

Peak Reverse Current =IRR= ta(di/dt)


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Reverse Recovery Characteristics

Abrupt Recovery

Reverse recovery time = trr= ta+tb

Peak Reverse Current = IRR= ta(di/dt)


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Diode Characteristics

Due to differences

between devices,

each diode has a

different voltageacross it.

Would like to

Equalize the

voltages.


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Series-Connected Diodes with

Voltage Sharing Resistors


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Series-Connected Diodes with

Voltage Sharing Resistors


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Example 2.3

Is1= 30mA, Is2= 35mA

VD= 5kV

(a)R1=R2=R=100k,

find VD1and VD2

(b)Find R1and R2for VD1=VD2=VD/2


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Example 2.3 (a)

s1

s2

1 2

D D1 D2

D2 D D1

D1 D2s1 s2

DD1 S2 S1

-3 -3

D1

D2 D D1

I = 30mA

I = 35mA

R = R = R = 100k

-V = -V - V

V = V - V

V VI + = I +

R R

V RV = + (I - I )2 2

5kV 100kV = + (3510 - 3010 ) = 2750Volts

2 2

V = V - V = 5kV - 2750 = 2250Volts


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Example 2.3 (a) simulation

D1

DIODE_VIRTUAL*

D2

DIODE_VIRTUAL**

R1

100kOhm

R2

100kOhm

U1

DC 1MOhm-2.727k V+

-

U2

DC 1MOhm-2.273k V+

-

V1

5000 V


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Example 2.3 (b)

s1

s2

DD1 D2

D1 D2

s1 s2

1 2

D2 12

D1 1 s2 s1

1

2 -3 -3

2

I = 30mA

I = 35mA

VV = V = = 2.5kV

2

V V

I + = I +R R

V RR =

V - R (I -I )

R =100k

2.5kV100kR =

2.5kV -100k(3510 - 3010 )

R =125k


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pn juction characteristics

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