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Can the PIV of a diode be "safely" exceeded?

Hi everyones thanks to read. Since a few weeks, i'm using the LightKeeper Pro from Ulta-Lit Tree Company (

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) to test and repair miniature lights sets (series-wired). I've found the Quick Fix Trigger utility very useful. as you can see on their website, it's based on a piezo igniter that sends a high voltage pulse through the lights set to activate (short) the shunt inside the bulb, that didn't do so when the bulb's filament burned out. I wanted to see how this system is built so i opened the unit. Here's two photos plus a schematic i've drawed for the igniter section. (Sorry, the symbol for the piezo igniter is probably wrong...i don't know the correct one).
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As i can see, the four diodes allow a peak reverse voltage of approximately

4Kv, wich is sufficient to break down the shunt's insulation inside the burned bulb(s) and complete the series circuit. Once completed, half of an AC cycle can flow through the four diodes, allowing the set to glow (dimly) and show which bulbs are burned and needs replacement. What leads me to my question (please look at the schematic) is: why the reverse voltage doesn't seem to damages those diodes? According to the piezo igniter's website (
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), the output voltage is at least 15Kv. With the four 1n4007 wired in series, i should get a peak reverse voltage of about 4Kv isn't? For what i know, a diode is destroyed once it's PIV is exceeded. I think i missed something when studying the basic operation theory of a diode. ;-) TIA for any useful reply.

-- Alain(alias:Kilowatt) Montréal Québec PS: 1000 excuses for errors or omissions, i'm a "pure" french canadian! :-) Come to visit me at:

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Reply to
KILOWATT
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It is only destroyed if the local heating is too great. Remember that a zener is a reverse biased diode that is intended to work in breakdown. When using several diodes in series to use them with a higher voltage, they need to be down-rated and it is usual to parallel them with capacitors to ensure an even distribution of voltage. So if the piv rating of a 1N4007 is 1000 V, it might be wise to downrate them to 700 V or thereabouts. The paralell capacitor value would depend on the frequency of operation.

--
Jim Backus OS/2 user since 1994
bona fide replies to j  backus  jita  
demon  co  uk
Reply to
Jim Backus

Thanks a lot for the infos... i appreciate.

-- Alain(alias:Kilowatt) Montréal Québec PS: 1000 excuses for errors or omissions, i'm a "pure" french canadian! :-) Come to visit me at:

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(If replying also by e-mail, remove "no spam" from the adress.)

Reply to
KILOWATT

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