Electronics > Beginners

Simple phase sequence detector using NAND gate

(1/4) > >>

vis5254:
I was able to get a circuit for this application searching a lot .
Does this circuit looks legit .
All I required was to have LED on when phase sequence was RYB and Led off when any another phase sequence arrives !
PNP - 2N4121
GATE IC - CD4011B

soldar:
A very quick look. Gates D2 and D3 form a flip-flop bistable which is set by phases 2 and 3. If then comes phase 1 gate D4 changes to state but if before phase 1 comes the flip flop is reset by L2 then D4 remains. In principle I see how it could work and it is easy enough to breadboard.

Be carefull with the three inputs. What voltages are we talking about?

Ian.M:
That circuit wont do what you want.  It is a phase sequence detector if you build it as far as the gates, that will output a low going pulse for approx 60 deg of the input cycle if all phases are present and L2 lags L1 and L3 lags L2, and if any phase is missing or the sequence is different, outputs a steady high level, but the transistor and LEDs part of the circuit is entirely bogus, with VL2 steadily illuminated and VL1 varying in intensity slightly due to the gate output (and passing far too much current for a 30mA LED).

LTspice sim attached.

There's also the issue that it uses Neutral as Vss for the logic circuit, and its input phases aren't isolated.  That's acceptable if its *JUST* a box on the wall with LEDs protected by lensed lampholders so there is no risk of contact, and its own isolated internal 12V supply, but is unsafe if its output goes to other low voltage circuits.

rstofer:
If you look around, you can find circuits that use only passive components and don't require an external source of power.

https://www.edn.com/design/power-management/4318736/Phase-sequence-indicator-uses-few-passive-components
https://m.eet.com/media/1129096/12890-figure_3.pdf

I used to do this stuff for a living.  I use the Knopp K-3 Phase Sequence Indicator

https://www.amazon.com/Knopp-K-3-Phase-Sequence-Indicator/dp/B07M687W4Y
 

soldar:

--- Quote from: Ian.M on May 25, 2019, 11:52:43 am --- That circuit wont do what you want. 
--- End quote ---

A tangent if I may. I have no formed opinion on that circuit and do not want to spend any time analyzing it but I am always very hesitant and very careful before I would say something posted by someone doesn't work because I figure whoever posted it had probably tested it and maybe it was just that I was not getting the idea.

Anecdote: Some years ago I was a newly arrived poster at some electronics forum and I posted a circuit. A certain old time member promptly dismissed it saying it could never work and he gave his analysis proving it. Even though I explained I had built it and knew many people who had built it and it worked fine the entire board supported the old member telling me, the newbie, how much the old man knew and how I could not hope to be at his level. The old member was adamant and nobody bothered to do their own analysis. This went on for a while until, I forget for what reason, maybe someone said they had built it, the case is that the old member admitted he was mistaken and the circuit I had posted was good.

At that point, everybody, and I mean everybody, turned to the old man and grovelled saying how he was "a class act" for admitting he was mistaken, etc. Not a word to me, the newbie, who had put up with so much shit.

I forget the forum and it does not matter anyway but it had a very cliquish atmosphere and I guess I did not last long. Newbies were definitely not welcome.

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod