Electronics > Beginners
Will this work (optocoupler over shunt)?
MK14:
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.
spec:
--- Quote from: T3sl4co1l on December 08, 2018, 09:21:13 pm ---
--- Quote from: spec on December 08, 2018, 08:18:45 pm ---Back again! Why don't you post a circuit for a bulb monitor instead of nit picking my circuit- Oh yes, I remember now, you did once and we saw the results of all your theories.
--- End quote ---
I still don't get your thing about circuits...
--- Quote ---You are nit picking. It is the architecture that is important. But as a matter of interest show me your calculations of how much current Q2 would conduct... 1uA, 1mA, ... 100A?
--- End quote ---
If architecture is important, the OP opened with it; indeed, I corroborated that from an analytical perspective. Just a matter of implementation then. Which means... yes, arguing about component choice as well as value. ???
It's about 1mA by the way, and no, it's very unlikely to cause a problem; but it's a poor design pattern that's very easily corrected, so it's always near the top of the list.
(One could also save even more with a "digital"/"prebiased" transistor, but the OP probably isn't making a million of these so normal discretes will be fine of course.)
--- Quote ---So what. It is not up to you to define what components I can specify.
--- End quote ---
Did I?
I'm hardly writing a dictionary over here... (cough, though I've probably posted a few of them's worth here over the years..)
--- Quote ---Besides I have had this argument before from theoreticians who like to display there superior knowledge.
--- End quote ---
Is that what you think I am, an armchair troll?
(Do you also make a habit of ignoring anyone who is right and outspoken, because clearly they must be an egoist?...)
--- Quote ---Those of us that design products that go into the market know that it is ridiculous to design right on the edge. I have seen quite a few 1N4148/1N916 fail when used for relay snubbing and inductance catching. The 1N4148 is designed for fast low level signals. Using your criteria practically every component in circuits are overkill.
--- End quote ---
Hm, did I define a criteria?
I like the implication that I haven't made or sold anything, though.
--- Quote ---I don't know what your problem is, but on a general note, can you please stop following me around EEV, which you have been doing since I recently started posting again. You, and a couple of others, are making a nuisance of themselves and wasting my time- like now.
--- End quote ---
Coincidence? I don't care to read or reply to every single thread, just those that look of interest of course.
Indeed, when I first noticed some of your posts, I thought it very interesting -- new design blood is an uncommon sight here. It's probably more than coincidence, if we're drawn to the same sorts of threads more than chance.
I'm sure this is my fault -- I enjoy a good rousing critique myself, and easily forget how sensitive others can be about their work. I also tend not to emote very well in written form. If it helps, try to read my posts with a disinterested voice. I generally want to be helpful, or try to be; eh, not that that necessarily means anything (I can think of more than a few bad people who claimed the same thing.. the context here is hopefully very different, at least).
--- Quote ---What I can't understand is that there are hundreds of circuits posted on EEC, some with obvious problems, where you could display your wide knowledge, but you say not a word. >:(
--- End quote ---
I probably tend to avoid threads with problems so obvious that the subject gives it away. Hmm, clearest example that comes to mind: an ESL* struggling with a technical subject AND a language barrier. I just can't be of much help when it's apparent that I won't be understood. :( Fortunately, the demographics here are quite diverse, and someone with better knowledge of the language barrier will be of greater help than I can.
*English Second Language.
Or, there's only so much talking I can do to a brick wall. That 30V 3A bench supply megathread is a classic example...
Cheers,
Tim
--- End quote ---
If I have misunderstood you, please accept my apologies. And I had no idea that English is your second language. 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. This has two bad effects. The OP doubts what I say and it takes me ages to reply to all the adverse comments. Quite often I have had to just leave a thread because of this. And the annoying thing is that people will make an adverse remark and when you prove that are wrong, they do not apologize or even discuss it.
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'.
I am not getting at you now, but while all these obvious points are being aired, the real problems are being missed. This has happened on a number of occasions with my circuits. By the way, errors are all part of design.
So sorry Tim, I have obviously misread your intentions.
Having said that, I genuinely appreciate it when someone points out an error of significance or gives new information. :)
spec:
--- Quote from: Hero999 on December 08, 2018, 09:34:53 pm ---
--- 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 ---
--- Quote from: spec on December 08, 2018, 07:55:17 pm ---I thought somehow that you would pop out of the woodwork >:(
--- 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 ---
Someone else might. I was going to ask the same question: what are the base-emitter junction of Q2 and the internal transistor inside the comparator vulnerable to? Please explain what you meant.
--- Quote from: spec on December 08, 2018, 08:18:45 pm ---Back again! Why don't you post a circuit for a bulb monitor yourself instead of nit picking my circuit- Oh yes, I remember now, you did once post a circuit after a lot of pushing and we saw the results of all your theories. It is a great shame that you do not apply your high standards to your own work. Tell me what are you? Are you a design engineer who has actually designed products for the market, or are you a perhaps a consultant of some kind who gives advice and has no responsibility for the end product. I don't like your aggressive tone either- there are ways of asking questions politely.
--- Quote from: T3sl4co1l on December 08, 2018, 07:07:25 pm ---What's R22-C4 for?
--- End quote ---
I don't believe that anyone who knows the first thing about electronic design would ask that question!
--- Quote from: T3sl4co1l on December 08, 2018, 07:07:25 pm ---Q2 doesn't turn off, needs B-E resistor.
--- End quote ---
You are nit picking. It is the architecture that is important. But as a matter of interest, show me your calculations of how much current Q2 would conduct... 1uA, 1mA, ... 100A?
--- Quote from: T3sl4co1l on December 08, 2018, 07:07:25 pm ---What's D6 for?
D7 is oversized, can be a 1N914 or less really.
--- End quote ---
So what. It is not up to you to define what components I can specify. Besides I have had this argument before from theoreticians who like to display there superior knowledge. Those of us that design products that go into the market know that it is ridiculous to design right on the edge. I have seen quite a few 1N4148/1N916 fail when used for relay snubbing and inductance catching. The 1N4148 is designed for fast low level signals. Using your criteria practically every component in circuits are overkill.
The other thing is that the 1N400x physical construction is more robust and less likely to fracture when fitted to the pins of relays, motorrs, etc. By contrast the IN418 is made of brittle and flimsy glass and with thin weedy self- leads is quite simply not suited, or intended for the job.
--- Quote from: T3sl4co1l on December 08, 2018, 07:07:25 pm ---I never got the fascination with using huge rectifiers on tiny relays... kids probably read it first in Forrest Mims' or something and kept doing it the rest of their lives? ???
--- End quote ---
What a patronizing fellow you are- I recon you still read Forrest Mims, whatever that is.
I don't know what your problem is, but on a general note, can you please stop following me around EEV, which you have been doing since I recently started posting again. You, and a couple of others, are making a nuisance of themselves and wasting my time- like now.
What I can't understand is that there are hundreds of circuits posted on EEC, some with obvious problems, where you could display your wide knowledge, but you say not a word. >:(
--- End quote ---
* Don't take it personally. Can't handle people nitpicking your circuits? Don't post them!
* Why not just answer the question, rather than making a sarcastic comment? It wouldn't have taken any longer. I believe R22 & C22 are for filtering the supply to the comparator. They're not needed in this, as it's not a linear amplifier which would be susceptible to a noisy supply, hence the question.
* He's right. Q2 won't turn off. The collector current will be dependant on the Hfe. R27 dominates and the Hfe varies widely so there's no point in including it in the calculation. IB = 12/560k = 21µA. Assuming Hfe = 400, IC = 8.6mA, which isn't much, but it will cause Q2 to heat more and the Hfe to rise. It shouldn't cause thermal runaway because the Hfe will stop increasing at safe current, but it's still bad design.
* The freewheeling diode only needs to be rated to carry the coil current. There's nothing wrong with overrating but don't be surprised when someone questions it.
You've also not said what D6 is supposed to do? It will never be forward biased!
I repeat, when posting a circuit, expect questions and criticism: both valid and invalid. I've learned when I saw someone's circuit which didn't look right, asked questions and criticised it, only to discover I was wrong, but it helped me so I don't regret it.
--- End quote ---
I wondered how long it would be before you popped out of the woodwork too. So here we go again. Your rhetorical question shows that you have not read or understood a word of my post. And who are you to tell me what and when to post. You presume too much.
As for answering the questions directly. I gave answers. There was nothing sarcastic at all. I did mean that if I needed to explain some of those questions that the answer would not be understood. Surely you can see that as the questions were so elementary.
But any way I have replied to the third party's post, now that he has explained his position.
spec:
--- Quote from: Hero999 on December 08, 2018, 09:34:53 pm ---
* Don't take it personally. Can't handle people nitpicking your circuits? Don't post them!
* Why not just answer the question, rather than making a sarcastic comment? It wouldn't have taken any longer. I believe R22 & C22 are for filtering the supply to the comparator. They're not needed in this, as it's not a linear amplifier which would be susceptible to a noisy supply, hence the question.
* He's right. Q2 won't turn off. The collector current will be dependant on the Hfe. R27 dominates and the Hfe varies widely so there's no point in including it in the calculation. IB = 12/560k = 21µA. Assuming Hfe = 400, IC = 8.6mA, which isn't much, but it will cause Q2 to heat more and the Hfe to rise. It shouldn't cause thermal runaway because the Hfe will stop increasing at safe current, but it's still bad design.
* The freewheeling diode only needs to be rated to carry the coil current. There's nothing wrong with overrating but don't be surprised when someone questions it.
You've also not said what D6 is supposed to do? It will never be forward biased!
--- End quote ---
Take a holiday - you just never let go do you. |O
spec:
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.
Another point is that, although you are all over EEC and assume the 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 does post a genuine question politely I am only to pleased to help out- as you must have seen on many occasions.
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