• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Golf Challenge:

Thread starter #1
In another forum I used to post what we called "Golf Challenges" ... which had nothing to do with golf but more of a challenge of the mind. It's just for fun and a way to exercise your mind.

Here is the setup:

Take an Opto-Isolator that has Zero crossing and a TRIAC output and use a standard output configuration ... i.e Figure 8 in the PDF below


The challenge is to design a circuit on the input of the Opto-Isolator that can accept 120VAC to 240VAC that may or may not be the same frequency as the output and may or may not be in the same Phase as the output.

No transformers allowed except for supplying the main AC power... IOW no small step-down transformers

I will post my solution Friday evening that I have tested that operates from 5VAC all the way to 290VAC (tested with a variac transformer).


Most Helpful Member
Standard capacitive coupled power supply type circuit. No real challenges there. Two capacitors, a resistor and common diode and a zener diode and away you go.

Depending on the working limits of the devices used I think I could squeeze at least 3 - 500+VAC through the circuit. ;)
Last edited:
Thread starter #3

That's one possible solution. Do you have a schematic you are willing to test and share?

It can be more of a challenge than you think ... the minimum forward current of the Opto's LED is 15mA and because of the Zero crossing, the LED needs to be "ON" during that time. If not, the output TRIAC will never turn on.


Most Helpful Member
I don't really see the point being there are at least half a dozen or more way this type of circuit could be made.

It all depends on the overall efficiency and working parameter limits the source of power will accept regarding amp draw and power factor plus possibly more depending on the voltage levels and frequencies in play.


Well-Known Member
tcmtrech, go ahead and show Beau Schwabe a schematic or 2 so lurkers like me can learn from your expertise, Please.
Even though it may be above my smart level


Most Helpful Member
Basically this without using R1 and CR1 zener diode is moved to D2 position.

Without the frequency or circuit power factor and efficiency limits defined this is as simple as such a circuit can get.
Last edited:
Thread starter #8
Without the frequency or circuit power factor and efficiency limits defined this is as simple as such a circuit can get
Ok, so lets define a few parameters then:

The Input voltage to the MOc3041 must be able to accept at least 120VAC to 240VAC ... 60Hz
The output of the MOC3041 must drive a standard TRIAC at the same Phase and frequency as the input ... Use Output circuit from Figure 8 in the PDF below

Bonus points if all components on the input side are rated at 250mW or below


So the input circuit is really what needs to be designed... As I said I will post my circuit tomorrow evening, I just wanted to see what others could come up with. With the Zero crossing aspect of the MOC3041 and the 15mA current requirement for the Opto-LED, the circuit solution may not be as straight forward as one would think.


Active Member
I'm still not clear. Drive it how? Or are you just concerned with the power supply (as in #6)?
Look forward to seeing your work.
Thread starter #13
Half a dozen of one, and six of the other? ... Seriously you guys are nitpicking over the orientation of the schematic? That's pretty sad actually. And I thought I would have people tearing apart the design itself.... Suppose that is next. :)


Most Helpful Member
Its basic level professional courtesy. Rather like using a written and or spoken language properly. If you can't be bothered to learn and use the language property the odds are you weren't bothered enough to learn anything else relating that which you speak of either properly.

Why use three 330 K resistors in parallel rather than one 110K? Presentation wise it gives the impression that you have poor circuit drawing and or working knowledge of the concepts in play. Same with having an overly complicated process to do a simple job and function.

A good part of one's perceived credibility is in their presentation. Bad presentation gives a strong image of bad performance, skill,and overall credibility.
Thread starter #15
Why use three 330 K resistors in parallel rather than one 110K?
... Because this board was done using SMT components... at 290V the Wattage through each of those resistors is right at 250mW which is the limit for 1/4 watt resistors. Using a single 110 K resistor or 100 K resistor would have required a 3/4 Watt resistor which is more heat than I want to dissipate in a single component. There is good reason why this circuit was designed the way it was.

I've been in the profession for more than 35 years and honestly I don't see an issue with the original schematic, you just rotated the schematic 180 Deg, and then the text again by 180 Deg.... So the TEXT was fine then since it is back where it started essentially? <smirk> ... Perhaps I am dyslexic and that would explain everything. This reminds me of a place I used to work about 25 years ago. One of the tests was to have the "new hire" study two schematics and determine the function of both schematics. One schematic was copied right out of a book, while the other schematic was electrically the same but simply drawn differently. The goal was to see if they could visualize outside of the box a little from the way they learned it in school, since a book is only someone eases opinion. ...and clearly we all seem to be opinion experts.


Well-Known Member
Not wanting to get involved in arguments here but 1206 resistors are generally only rated for around 200V.

That aside, funny seeing this after spending last night designing a zero crossing system for some other stuff I'm working on . Mine was much dirtier with a transformer for the common zero cross though.


Most Helpful Member
The goal was to see if they could visualize outside of the box a little from the way they learned it in school, since a book is only someone eases opinion. ...and clearly we all seem to be opinion experts.
Ah, but we are not doing job interviews nor do most of us care to have to translate what looks like others laziness to work with them. :rolleyes:

The formal standards of the established profesional community set the process and method of communication between them. Not who's supposed medical excuses for being lazy. Handicapped victim status does not fly as an excuse for sloppy workmanship, especially given many of us her are also slightly dyslexic and have no trouble making our presentations meet basic established standards so that other don't have to put great effort to understand what we are trying to say and show.

orwoudlth thteht otudonet boeht hcendnaproffersing ewith spelsls what tI psot and hsut leth you rfigtuernw uto ut ong yhtoeut owns? itint the snaem snetnavete fal. jsut ontne clanfe dup and madme ptreantalbel.:confused:

(Or would you prefer that I don't bother with proofreading and spell checking what I post and just let you figure it out on your own? It's the same sentence after all, just not cleaned up and made prestable. ) :rolleyes:

See the problem of your reality and expectations? :confused:
Thread starter #18

I can see you and I will get along just fine.... Like I said, thanks for being a good sport and being the only person to post a schematic other than knarfi


Most Helpful Member
No problem. It's a good forum and most of us are pretty easy to get along with so long as nobody tries to push nonsensical excuses for weak minded or sloppy work or going around proudly making bold claims that are easily refuted by reality. ;)

As for your circuit, it's clever but the 15 ma current limiter section is likely not really necessary being the zero cross gated sections inherent voltage limiting actions will keep the voltage stable enough to get by with a simple current limiting resistor in its place.


Well-Known Member
I think you drew your schematic wrong, I copied it to spice and it didn't work until I changed a wire, then it simmed correctly. You had the rectified voltage going straight to the optical isolator without handling it. YES - NO?


Latest threads

EE World Online Articles