1. Home
  2. Hobby Electronics Basics
  3. Can the PIV of a diode be "safely" exceeded?

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 (

formatting link
) 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).
formatting link
formatting link
formatting link
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 (
formatting link
), 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:

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

Reply to
KILOWATT
Loading thread data ...

No, the PIV is just the point (well, minus some margin) where the diode should be expected to "break down" and conduct in the "wrong" direction. But "break down" may be giving you the impression that the diode is damaged in the process, when that is not at all the case. Diodes may safely be operated past the reverse breakdown point IF the current through the diode is limited (to whatever value is safe depending on the specifications of the diode in question). This is, in fact, the normal operating mode for a "Zener" diode, which is simply a diode which has a very abrupt reverse-breakdown point (and usually one which has been intentionally designed to be a relatively low (and therefore useful, for such things as regulators) voltage.

The way a diode is generally used as a rectifier, though, there would not be any current limiting provided, and exceeding the PIV would in general be a one-time event...:-)

Bob M.

Reply to
Bob Myers

Probably just for safety... the wiring/diodes probably aren't rated to carry more than 3A, so they'd rather have the fuse blow than the diodes or the wiring melt down.

It's a clever product, IMO!

Reply to
Joel Kolstad

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:

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

Reply to
KILOWATT

Yess... i normally avoid crossposting because some people see this action as "bad" even if i perfectly agree with you, Rich.

Reply to
KILOWATT

The 1n4007 are rated @ 1amp so the 3amp fuse seems to protect only the wiring inside. ;-)

carry

Reply to
KILOWATT

Alain,

You are observing the action of avalanche. Most modern high voltage diodes are designed to withstand various amounts of reverse avalanche energy absorption. Diodes that are applied in series should be tested for this avalanche characteristic. The information given for the piezo out put voltage of 15kv does not happen. The diodes clamp the voltage at about 4500 volts.

Ray

to

based

to

approximately

(dimly)

piezo

formatting link
),

i
Reply to
rayjking

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.