making up zener diodes

75+15=90

ok will it work?

It would work as a 90 volt zener, not as a 100 volt one.

--
Dyna

All rights reserved. All wrongs avenged.

thankyou for the info

zack

"`ZACK`"

** Aside from your math error, the basic idea is 100% OK.

Strings of zeners wired in series up to 50 are seen in commercial devices.

It works.

..... Phil

Will give 90v not 100v (75v+15v=90v)

No problems with series zeners though as long as they are the right wattage. I used 3x 30v in series once to make a 90v zener. No problem.

"kreed" "`ZACK`"

** Quad used no less than 32 x 220 volt zeners wired in series to make a voltage limiter for their ESL63 speaker.

Yep - it limited at +/- 7000 volts !!!!

See list of schems in the middle of this page:

..... Phil

Very impressive. Not that I can think of another practical way to do it.

Another "series zener" application I was told of years back , is in very long distance communication cables. (probably also undersea submarine cables). In the example I was told of (a 300km land based cable) in order to power all of the the many inline booster/repeater boxes they had a single supply cable in the line that was connected to

+750vdc at one end and -750vdc at the other end. All the "booster" boxes in the line would wired in series along this high voltage line that was at 1500v potential end to end. The earth would be the return.

At each box, they would put a zener diode in series with this high voltage line and draw the unit's supply rail voltage from across this zener. For example, if each box required 50v, and there were 30 boxes , there would be a total of 30x 50v zeners in series in the

1500v line.

(I cant remember exactly how many boxes were used, or the supply voltage for each - just used these figures as an example)

Even with fibre optic cables being used these days, they more than likely still need to be boosted every so many KM over long runs ? so this method no doubt would still be used for powering boosters.

If series zeners are reliable enough for extremely critical applications like undersea cables, then they are reliable enough for pretty much anything as far as I'm concerned.

Providing the tolerance is OK (5% per diode) and you are drawing the minimum current to get the zener effect.