Good day folks. This might be a silly question, but how much voltage can I pump through a zener diode ? I know the CURRENT should stay below a safe margin to avoid blowing the diode, but what about the voltage ? In the traditional regulator setup where I have a resistor in series with the load and the zener, provided the resistor is large enough to avoid excessive current, is there a maximum "input" voltage to such a circuit ? Again, please excuse me if this is a basic building-block question which I should be familiar with, but hey....the more you learn......
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Maximum voltage through zener diode
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Re: Maximum voltage through zener diode
The power through anything is P=V*I.
Say you have a 10w 1.8v zener diode broken down. To dissipate 10w you would be sinking 2 amps at 5v. Sinking 2v would be 5 amps. sinking 10v would be 1amp. sinking .2amps would be 50v. at 110v you would sink .09 amps for 10w.
Its linear.
Expanding into the equation:
P=V*I, so we have 10=5*I. we need to solve for I. Through some simple high school math: P/V=I, so 10/5=2
So its P/V=I for current, V*I=P for watts, and P/I=V For volts.
For a functional example:
Say we need the amperage of a conventional 150w light bulb. 120v, at 150w gives us 150/120=1.25. 1.25 amps for said bulb. We can now plug said numbers into the other functions to check our work.
150/120=1.25 (Amps)
120*1.25=150 (Watts)
150/1.25=120 (Volts)
Larger numbers are the same as well. Say, 2Kv at 1.5Kw.
1500/2000=0.75 (A)
2000*0.75=1500(W)
1500/0.75=2000(V)
This is basic stuff, yes. Another rule to live by is the 90% rule. When rating non-precision components like resistors and the like, add an extra 10% to the expected max rating, and size accordingly. Say you have a resistor that you want to sink 3/4Watt into. Rate it for 1w. If you have a 10v circuit you plan to add a capacitor to, use a 16v capacitor. If you are making a 9 amp switching circuit use a 10 amp FET. Etc...
This knowledge is holdover from the days of gone with tube radios and whatnot, so that 90% rule may be outdated.Last edited by goontron; 08-04-2017, 08:47 AM.Things I've fixed: anything from semis to crappy Chinese $2 radios, and now an IoT Dildo....
"Dude, this is Wyoming, i hopped on and sent 'er. No fucking around." -- Me
Excuse me while i do something dangerous
You must have a sad, sad boring life if you hate on people harmlessly enjoying life with an animal costume.
Sometimes you need to break shit to fix it.... Thats why my lawnmower doesn't have a deadman switch or engine brake anymore
Follow the white rabbit.
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Re: Maximum voltage through zener diode
To take it one step further and put it into practice (not literally please because someone will get hurt ): if I have 230v from the wall socket, turn that to DC and stuff it into a 5w zener, I'd only be able to draw a maximum of 0.02a from said circuit, correct ? Don't know of what use that would be.....lighting an LED perhaps ?Wattevah...
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Re: Maximum voltage through zener diode
You do pump the Voltage, you forcing the current through the Zener, the Zener will try to maitain the rated Zener Voltage.
You also need to realize how to use the Zener.
What is the Voltage rating of the 5W ZENER? 5V? 10V, 100V. You know the Wattage, you know the Zener Voltage then you can find what the current rating is.
You also do not want to put the Zener across the power source that has high Voltage than the Zener. I.E. put 6V Zener across 12V power source. Try it an see what happen for yourself.
https://www.digikey.com/en/maker/blo...e17bc61e2640f3Never stop learning
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http://www.badcaps.net/forum/showthr...956#post305956
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Inverter testing using old CFL:
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Re: Maximum voltage through zener diode
Originally posted by Dannyx View PostTo take it one step further and put it into practice (not literally please because someone will get hurt ): if I have 230v from the wall socket, turn that to DC and stuff it into a 5w zener, I'd only be able to draw a maximum of 0.02a from said circuit, correct ? Don't know of what use that would be.....lighting an LED perhaps ?Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
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Re: Maximum voltage through zener diode
That's what it can dissipate before blowing up. Zeners can't limit current. That's a resistors task.
The most common use for Zeners, at least in my field, is voltage limiting. Say you have an expensive 5v powered device, and you have a crappy chinese 5v wall wart that you don't trust to power it. You could use a 5.8v zener in inverse parallel across the incoming from the PSU to clamp any voltage above 5.8v to ground. This is actually done in cheap capacitive dropper PSUs commonly.Things I've fixed: anything from semis to crappy Chinese $2 radios, and now an IoT Dildo....
"Dude, this is Wyoming, i hopped on and sent 'er. No fucking around." -- Me
Excuse me while i do something dangerous
You must have a sad, sad boring life if you hate on people harmlessly enjoying life with an animal costume.
Sometimes you need to break shit to fix it.... Thats why my lawnmower doesn't have a deadman switch or engine brake anymore
Follow the white rabbit.
Comment
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Re: Maximum voltage through zener diode
Originally posted by goontron View PostThat's what it can dissipate before blowing up. Zeners can't limit current. That's a resistors task.
The most common use for Zeners, at least in my field, is voltage limiting. Say you have an expensive 5v powered device, and you have a crappy chinese 5v wall wart that you don't trust to power it. You could use a 5.8v zener in inverse parallel across the incoming from the PSU to clamp any voltage above 5.8v to ground. This is actually done in cheap capacitive dropper PSUs commonly.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
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Re: Maximum voltage through zener diode
^ yeah, the lone zener is for low power systems (100s of mA).Things I've fixed: anything from semis to crappy Chinese $2 radios, and now an IoT Dildo....
"Dude, this is Wyoming, i hopped on and sent 'er. No fucking around." -- Me
Excuse me while i do something dangerous
You must have a sad, sad boring life if you hate on people harmlessly enjoying life with an animal costume.
Sometimes you need to break shit to fix it.... Thats why my lawnmower doesn't have a deadman switch or engine brake anymore
Follow the white rabbit.
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Re: Maximum voltage through zener diode
Originally posted by budm View PostYou also do not want to put the Zener across the power source that has high Voltage than the Zener. I.E. put 6V Zener across 12V power source. Try it an see what happen for yourself.
To be fair, I was thinking of a 12v zener on a 230v supply straight off the mains....stupid, I know, but I wasn't actually going to try it - it's just to learn something about zeners in general and WOULD happen.
EDIT: the above setup would of course have the limiting resistor, otherwise it would go boom instantaneously, DUUH...I'm not that dumbWattevah...
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Re: Maximum voltage through zener diode
Well you do not need 230V just to do the experiment, just use your DC variable bench power supply that can supply lots of current that has Volt and current meters then hook up may be 3V zener at the output of the power supply and then crank up the Voltage see what happen, easy enough.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
Comment
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Re: Maximum voltage through zener diode
Originally posted by budm View PostWell you do not need 230V just to do the experiment, just use your DC variable bench power supply that can supply lots of current that has Volt and current meters then hook up may be 3V zener at the output of the power supply and then crank up the Voltage see what happen, easy enough.Wattevah...
Comment
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Re: Maximum voltage through zener diode
What a wasted thread.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
Comment
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Re: Maximum voltage through zener diode
Ok, for some reason I haven't seen some of your replies (notifications were a bit late), so that's why my replies probably didn't make sense...
Now then, let's clear the mess up:
Originally posted by budm View PostShow us the diagram and show us how you come up with 0.02A.
Math: supposing the zener is rated for 5w. At 230v, 5w would mean 0.02A (5/230v=0.02, unless I'm somehow wrong). Now if the zener is a 10v one and I just had a piece of wire in place of the resistor, it would begin conducting immediately (since 230 is higher than Vz) and would draw immense current from the supply, since there's nothing stopping it from doing that - POP ! To prevent that, you'd size up the value of the resistor accordingly to keep the maximum current through the diode below 0.02a which would correspond to 5w....I may be wrong of course, so feel free to correct me again, that's the whole idea. It's all in my head, but I'm not good at explaining it back to othersWattevah...
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Re: Maximum voltage through zener diode
Yeah, a lot of facepalm and head throbbing conclusions here... head is spinning...
Key points:
1. 5W means 5W max is dissipated by the diode. This indicates max current that can pass through the diode when coupled with the zener voltage. A 10V zener means P=VI=5W=10V*I meaning I=500mA through the zener.
2. Connecting a resistor and zener in series is kind of useless. We need to know the load in parallel with the zener being regulated to really know what we're talking about. The variability of the load will dictate whether or not a zener regulator can be used.
3. If you compute back with that useless example above with 10V zener and 230VDC supply and no load in parallel with the zener, 220V would need to be dropped across the resistor. 220V*0.5 = 110W dissipated in the resistor by itself regardless of its value . THIS is the problem of these zener supplies.
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Re: Maximum voltage through zener diode
you can use something like this
https://electronics.stackexchange.co...erter-lossless
(the first example) The capacitor is here used for AC as serial resistor but without dispating to much heat because of its capacital reactancy(current is shifted against voltage)
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Re: Maximum voltage through zener diode
Originally posted by fester View Postyou can use something like this
https://electronics.stackexchange.co...erter-lossless
(the first example) The capacitor is here used for AC as serial resistor but without dispating to much heat because of its capacital reactancy(current is shifted against voltage)Wattevah...
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