Understanding Peak Inverse Voltage (PIV): Why Is It Important?

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Discussion Overview

The discussion revolves around the concept of Peak Inverse Voltage (PIV) in diodes, particularly its significance in preventing diode breakdown during reverse bias conditions. Participants explore the relationship between PIV and the maximum voltage from AC generators, as well as implications for different rectification methods.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • Some participants express confusion about the definition of PIV and its importance, particularly why it must exceed the maximum voltage of the AC generator.
  • One participant explains that PIV is crucial to ensure the diode does not break down when reverse voltage is applied, emphasizing that it refers to the maximum voltage the diode can withstand, not the voltage applied.
  • Another participant describes the charging of a filter capacitor by a rectifier diode, noting that when the input polarity reverses, the diode experiences a peak negative voltage that is roughly double the peak input voltage.
  • Questions arise regarding the formula indicating that PIV must be greater than the maximum voltage (Vm) in both half and full rectification scenarios.
  • Concerns are raised about the reliability of two reverse-biased diodes sharing the applied voltage equally, particularly in bridge configurations where two diodes may not equally distribute the voltage during polarity reversal.

Areas of Agreement / Disagreement

Participants generally express confusion and seek clarification on the relationship between PIV and rectification methods. There are multiple competing views regarding the implications of PIV in different configurations, and the discussion remains unresolved.

Contextual Notes

Participants highlight the need for understanding the conditions under which PIV is applied, including the effects of capacitor charging and the behavior of diodes in various rectification setups. There are unresolved questions about the mathematical relationships involved.

Who May Find This Useful

This discussion may be of interest to students and practitioners in electrical engineering, particularly those studying diode applications in rectification circuits.

queenstudy
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i read this sentence like a 100 times and i still don't get it please can anyone help me??
PEAK INVERSE VOLTAGE (PIV):
PIV is the maximum reverse bias voltage which can be applied safely to a diode without its breaking down. Beyond this voltage a diode breaks down
they say the PIV must be greater than the maximum voltage of the sin form of the ac generator why?
 
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This is so that the diode will not break down when the voltage is reversed and it's supposed to be 'off' - which is what diodes are used for.

(PIV refers to the Max PIV that the diode can stand - not the actual voltage you apply)
 
queenstudy said:
i read this sentence like a 100 times and i still don't get it please can anyone help me??
PEAK INVERSE VOLTAGE (PIV):
PIV is the maximum reverse bias voltage which can be applied safely to a diode without its breaking down. Beyond this voltage a diode breaks down
they say the PIV must be greater than the maximum voltage of the sin form of the ac generator why?

When a rectifier diode conducts and it charges a filter capacitor, it charges the capacitor up to the full positive voltage of the input waveform (minus a small diode voltage drop).

Now, when the input polarity reverses, the diode gets a peak negative voltage on its anode, but it still has the positive voltage of the capacitor on its cathode.

So, it has roughly twice the peak input voltage across it in reverse. This voltage situation is called the peak inverse voltage and the diode needs to be able to cope with it without breaking down.
 
what about the formula PIX greater than Vm in both half and full rectification why??
thank you guys for the help
 
You cannot rely on the two reverse biased diodes sharing the applied volts equally.
 
queenstudy said:
what about the formula PIX greater than Vm in both half and full rectification why??
thank you guys for the help

For the same reason as above, if the diode charges up a capacitor, that voltage will add to the reverse voltage across the diode when the polarity from the transformer reverses.

This applies whether the rectification is half wave, full wave or a bridge. (In a bridge, there are two diodes in series when the polarity reverses and as Sophie mentions, they may not share the voltage equally.)
 

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