A Zener diode allows current to flow from its anode to its cathode like a normal semiconductor diode, but it also permits current to flow in the reverse direction when its “Zener voltage” is reached.
| Circuit Symbol |
Working
• Zener diodes have a highly doped p-n junction.
• When junction is reverse biased a small reverse saturation current flows Is.
• When sufficient voltage is given the junction breakdown and large reverse current flows.
| Diode connection |
• If a resistor is connected in series, then the current can be limited and power dissipation can be controlled so that the device does not damage.
• The diode may operate continuously under such condition.
• The current returns to normal level if voltage is reduced below breakdown level.
| IV Characteristics |
It is used as:
• Voltage reference sources
ü the breakdown voltage is designed to remain stable for a wide range of current
Breakdown Mechanism
ü Zener Breakdown
ü Avalanche Breakdown
Zener Breakdown
• In a very narrow depletion region electric filed strength is high.
• High electric filed intensity cause the electrons to break from their atoms .
• Thus the depletion region starts to conduct.
• It usually occurs when reverse bias voltage is <5 V.
• This effect is also called as Ionization by electric field.
Avalanche Breakdown
• When depletion region is wide, the reverse saturation current gives energy for the electrons to collide with other electrons in the depletion region.
• Avalanche effect is termed as production of more free electrons by the Collison of electrons.
• This is also termed as Ionization by Collision
This breakdown happens >5V
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