127v AC regulator using zener diode  - Page 1
Forum section: electronics / projects

author: GoatZero
author_rank: Regular Contributor
timestamp: October 23, 2013, 03:17:06 am
content: Electronics engineering student here, school project time, we are supposed to use diodes and make a proyect that its supposed to be helpful and usefull along our careers, it doesnt have to be complicated as long as we design itSince the mains at some labs (a bit old some of them ) are giving up to 137 volts and at home at night the mains voltage can go up to 132 volts i decided to attemp to use a zener diode as a voltage regulatorSo a portable voltage regulator, this way if i decide to plug it at the lab or at home and be absolutely sure im using 127v when its plugged instead of 137 or morehowever i still dont understand completely how power and current relation works, i do knowP=VISo at school this would look something like thisP=(137)(X)X being whatever current the load needs to workhowever how can i know how many watts does the resistor to protect the zener diode has to be for this AC aplication if i will never know how much current the load of my breadbord circuits will pull so how can i make this without knowing that ?also, i tried looking for a 127v Zener diode and i did not find anyso in the end i askUp to now i have been rectifing and regulating DC however, im wondering if its posible to regulate AC using diodes without taking out half AC cycle (because zener is still a diode), other wise my brain somehow tells me its not possible using diodes, but i cant imagine any other way to do thisDo 127v zener diodes Exist? (already tried newark, mouser and digikey only found 120v and 120v zeners)How can i do this,? mostly any feedback or ideaspicture semirelated, (same application but DC), what i want to do just take out the transformer, rectifier bridge and the capacitor

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: October 23, 2013, 03:41:51 am
content: OMG no.Make a low voltage psu as per your diagram, it will be safer and far more useful.Also fix up the bridge rectifier in that diagram.A regulator has specific meaning in the realm of electronics, it is not used for what you are describing.

author: david77
author_rank: Frequent Contributor
timestamp: October 23, 2013, 03:52:05 am
content: You can not "regulate" AC with a Zener diode. I would suggest you stay away from anything to do with mains for now, there's a real danger you may kill yourself or burn down the house.Stick to something below 24V for now.If your nominal mains voltage is supposed to be 127V then 132 or even 137V will not be a problem for your appliances, they can tolerate that. Rule of thumb: +20% mains voltage should not be a problem for anything you plug in the mains.

author: minime72706
author_rank: Frequent Contributor
timestamp: October 23, 2013, 04:10:18 am
content: I don't think that an issue really exists here, but the only way I'd really do it is using a VARIAC (adjustable transformer). This really shouldn't be an issue that you need to solve. Mains-rated stuff should typically function between 95VAC and 130VAC when we're not talking about 220VAC/50Hz systems. You'll rarely see a mains voltage below 110VAC and I personally typically see 115VAC to 125VAC around where I am.If you're designing something that is THAT sensitive to mains voltage, you're doing it wrong.If you had a legitimate reason for wanting to "Regulate AC", you'd basically do it with a variable transformer or maybe a "voltage divider" using complex impedances. As you probably know, using resistors will get you nowhere.

author: Stonent
author_rank: Super Contributor
timestamp: October 23, 2013, 04:16:58 am
content: Zener diodes trim a voltage down when installed in a reverse fashion. When installed in a forward fashion electricity will flow unimpeded for the most part.If you use for instance a 10V zener, you'll get an asymmetrical sine wave with one side higher than the other. If you then rectify that you'll get alternating DC pulses of 127 and 117.Edit: Ok I looked at your schematic and see you're trying something else. I'm not sure how that circuit will work but it doesn't look right to me. I suspect you'll just end up with an zener diode that burns up or worse explodes. With 127 volts going through it to ground.

author: GoatZero
author_rank: Regular Contributor
timestamp: October 23, 2013, 05:13:05 am
content: thanks to all, at least now i know its not that easy or at least cheap

author: amyk
author_rank: Super Contributor
timestamp: October 23, 2013, 05:55:36 am
content: They don't make zeners go that high... if you want mains regulation a multi-tapped transformer + relay switching is usually the preferred solution.

author: Jon86
author_rank: Frequent Contributor
timestamp: October 23, 2013, 06:14:40 am
content: Hmm, I'd say go with some kind of low voltage zener regulator, this circuit seems a little dodgy to say the least. Maybe you could do something that involves clamping/protecting input signals?

author: ConKbot
author_rank: Super Contributor
timestamp: October 23, 2013, 12:19:46 pm
content: This application is actually a good choice for a ferroresonant transformer, as they output a fairly constant voltage with a changing AC input. But they cost a good bit

author: grumpydoc
author_rank: Super Contributor
timestamp: October 23, 2013, 01:45:13 pm
content: Quote from: amykActually, they do. Farnell lists zeners up to 270V, as does Mouser (in fact they have a non-stocked one at 330V).QuoteSee above and perhaps check how you were searching the website.Please don't think you can try to use them to "regulate mains" though. That's.......not going to workTo be fair I note the OP did say:QuoteSo Ithinkthey were "just asking".Project using diodes? - how about a simple AM radio with diode detector.