PN-Junction%20Diode%20Characteristics

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PN-Junction Diode Characteristics
Forward Bias --- External battery makes the Anode
more positive than the Cathode --- Current flows
in the direction of the arrow in the
symbol. Reverse Bias --- External battery makes
the Cathode more positive than the Anode --- A
tiny current flows opposite to the arrow in the
symbol.
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Graphical PN-Junction Diode V-I Characteristic
Forward Bias Region
Reverse Bias Region
Reverse breakdown
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Mathematical Approximation
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Ideal PN Junction Diode V-I Characteristic
Forward Bias Short Circuit
Reverse Bias Open Circuit
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Diode Reverse Recovery Time
ta is the time to remove the charge stored in the
depletion region of the junction tb is the time
to remove the charge stored in the bulk
semiconductor material
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Reverse Recovery CharacteristicsSoft Recovery
Reverse recovery time trr tatb Peak Reverse
Current IRR ta(di/dt)
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Reverse Recovery CharacteristicsAbrupt Recovery
Reverse recovery time trr tatb Peak Reverse
Current IRR ta(di/dt)
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Series-Connected Diodes

• Use 2 diodes in series to withstand higher
  reverse breakdown voltage.
• Both diodes conduct the same reverse saturation
  current, Is.

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Diode Characteristics

• Due to differences between devices, each diode
  has a different voltage across 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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Series-Connected Diodes with Voltage Sharing
Resistors

• Is Is1IR1 Is2IR2
• IR1 VD1/R1
• IR2 VD2/R2 VD1/R2
• Is1VD1/R1 IS2VD1/R2
• Let R R1 R2
• Is1 VD1/R Is2 VD2/R
• VD1 VD2 Vs

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Example 2.3

• Is1 30mA, Is2 35mA
• VD 5kV
• (a) R1R2R100k?, find VD1 and VD2
• (b) Find R1 and R2 for VD1VD2VD/2

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Example 2.3 (a)
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Example 2.3 (a) simulation
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Example 2.3 (b)
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Example 2.3 (b) simulation