Electronics > Beginners

Will this work (optocoupler over shunt)?

<< < (10/11) > >>

Zero999:

--- Quote from: spec on December 08, 2018, 10:34:36 pm ---About the base emitter vulnerability. That is a surprising question but if I gave an answer, like I did about the diode, you would not accept it and there would be endless posts going round and round, just like with the diode.
--- End quote ---
I would not accept it, because you didn't provide any explanation as to why the base-emitter junction is vulnerable. I admit i missed the part about the higher on losses, which is true, an emitter follower will have higher on losses, than a common emitter configuration. I suppose one could say the power dissipation will be higher, thus making the transistor more vulnerable to overheating, but in this case the power dissipation is only 110mW, which is well within the the rating of the BC327.


--- Quote from: spec on December 08, 2018, 06:43:33 pm ---
--- Quote from: Hero999 on December 07, 2018, 11:17:27 pm ---
--- Quote from: ArthurDent on December 07, 2018, 06:45:10 pm ---Here is my final variation of the detector that may address some concerns and, like I said, if any of these various circuits were actually built and tested there could be minor or major changes that might come to mind. I think stenespen now has enough information so they can pick and choose what they think might be best for them and try that circuit.

--- End quote ---
That will not overcome the issue of the transistor clipping the comparator's output.

If you want to use the comparator's non-inverting input for positive feedback and don't want to use a MOSFET, then use a PNP BJT, but the logic will be reversed.

You seem not to believe me when I said the relay coil's inductance doesn't generate any noise. Where did you get that idea from? It's compete nonsense!

--- End quote ---
Q2 e/b junction is vulnerable here, as is the open collector transistor in the comparator. Also, you would be losing more drive to the relay than with a saturated collector arrangement, like the original.

--- End quote ---

Someone else asked the same question, but you didn't say why.

--- Quote from: spec on December 08, 2018, 07:55:17 pm ---
--- Quote from: T3sl4co1l on December 08, 2018, 07:04:10 pm ---Vulnerable to what?
--- End quote ---
If you need to ask- you would not understand the reply

--- End quote ---


--- Quote ---Another point is that, although you are all over EEC and assume to position of resident expert on all matters, you are just a member like everyone else and it is not your place to tell me that I should expect this or that or that I am obliged to explain anything.This is an example of your circular arguments. Although if someone posts a genuine question politely I am only to pleased to help out- as you must have seen on many occasions.

--- End quote ---
Although I post regularly, I'm no expert on all matters, for example I know very little about programming, so I leave that to others.

You're right that no one is obliged to explain anything, but people will not accept your answers to their questions, without a clear and logical explanation.

spec:
Your reply above indicates that you havn't taken in a word that I have said.

Please keep out of my hair and I will do the same to you.
________________________________________________________________________________________________________

Zero999:

--- Quote from: MK14 on December 08, 2018, 09:45:24 pm ---The idea of this circuit, is to be SIMPLE and made out of jelly bean parts. It is partly based on the OP's original circuit.
It does have approximately 1.5 to 2 Volts drop across the diodes, but on the other hand, simplifies things for beginners.
Edit: Updated resistor values. Feel free to adjust resistor values as necessary.
--- End quote ---
Yes that'll work, but the logic is reversed. R3 and D3 could go in the emitter, to make the LED off when the lamp is blown and on, when it's working.

I agree, the circuits have become outlandishly complex and overkill, but that's feature creep and people having fun, posting different solutions. :)

MK14:

--- Quote from: Hero999 on December 08, 2018, 11:44:13 pm ---Yes that'll work, but the logic is reversed. R3 and D3 could go in the emitter, to make the LED off when the lamp is blown and on, when it's working.

I agree, the circuits have become outlandishly complex and overkill, but that's feature creep and people having fun, posting different solutions. :)

--- End quote ---

I guess the OP, hasn't necessarily been 100% clear on, if they want it on or off, when faulty.

I based the logic, on a diagram, similar to the following one, shown below.
I.e. It ONLY lights up when the bulb is blown/faulty and needs replacing.

T3sl4co1l:

--- Quote from: spec on December 08, 2018, 09:55:54 pm ---If I have misunderstood you, please accept my apologies. And I had no idea that English is your second language.

--- End quote ---

Not me, I mean examples of threads by original posters (OPs) that are.



--- Quote ---Maybe that is partly the problem. But do try to see it from my point of view too. You and another regularly contradict/give the impression of contradicting what I say.
--- End quote ---

It is easy to misread criticism as contradiction, but please do not jump into a defensive position when you see such a statement!

All that I have said about myself, probably applies in part to Hero999 as well.  He's been here longer than I have, and I don't recall any particular disagreements.  If I may be so bold: you seem to be the common denominator here, so please, take it easy! :)



--- Quote ---I hate to say this but in your post, there was only one thing that was of any significance, that is about the base resistor. You are absolutely right, but do you think that I would not have known that. And to be specific the current that could flow through the transistor (worst case) will have no effect on the operation of the circuit.

You could have just said: 'Just in case, a resistor across the e/b transistor would be good design practice'.
--- End quote ---

Could.

I'm very thorough in my work, and I try to present that here in the hopes that others will pick up on it.  The design process can go infinitely deep, but you only need to go finitely far to get an arbitrarily good result.  That is, it is a process where successive approximation yields excellent results (as opposed to some processes that diverge -- sometimes this happens in SPICE for example, with subsequent hair-pulling..).

So, in that process, rather than leave it at the zeroth or first approximation, I do a quick second-order check to verify that the first degree is, in fact, the correct stopping point, and that no big surprises are likely to show up.

And so, in that process, I make observations, look for weird things.

If I see something that doesn't have an obvious purpose, I ask.  I mean, asking questions are how we find out about things, right?  Can I never ask you a legitimate question ever?  That's really unfair, man.

To paraphrase Freud, sometimes a question is just a question.

Sometimes a question reveals insight.  Is there actually no reason for R22-C4?  Might as well remove it, then.  Fewer parts in a discrete design, easier to assemble, less to go wrong.  That's valuable.  Or replace it with something better suited, like if inductive spikes and reverse protection are a concern, then a TVS diode would be even better.  (And if this is an automotive application, both are likely!).

And so our circuits can improve, and we learn more breadth of knowledge in the process. :)

(Professionally, a typical response to a question like this is: "it was copied from a previous design".  That's a possible warning sign -- many designs build up technical debt just as much as software or facilities do.  But it also at least strongly implies that it's passed functional and regulatory checks before, and is worth consideration.  Another typical response is: "yeah, we're not really sure there, we just pulled from the appnote", and useful improvements can be made -- and often prove necessary!)

Tim

Navigation

[0] Message Index

[#] Next page

[*] Previous page

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