You still have not clearly explained yourself. You have described more than one circuit and done it all in bits and pieces so that it is impossible to tell what comment goes with what circuit. You don't use proper language so that it is hard to tell what you are trying to say and you say that your measurements show things don't work without giving enough specifics.
"I've even tried to enlarge the bias-current to way above that and use three diodes instead of two to account for the lesser voltage-drop per diode." This is the comment that got me into the conversation. If you are talking about a circuit with the diodes in series with the load, a "lesser voltage-drop per diode" is impossible when the current it higher. I still don't know for sure with what circuit you measured this change.
I don't think it really matters. You have also said things like the value of the resistor was too high and there was not enough voltage to drive the card. If you can't get a resistor of the correct value, none of these circuits will work. Since you are working with parts from your scrap box there is no reason to believe that you will be able to make any given circuit work correctly due to improper biasing.
If you want to use your circuit that's fine. But diodes can be used to adjust a 5 volt supply down to 3.5 volts which although may not be within a 5% spec, will power a 3.3 volt device without damage and will work correctly. To say this circuit won't work is wrong. You can say you could not make it work, but that is likely due to the lack of parts in your bin rather than any limitation in the circuit.
Meanwhile, the rest of us will use three terminal regulators since they are both effective, cheap and readily available to us. Other than hobbiest use of series diodes, I literally have not seen anyone build their own regulator circuit in a real design in the last twenty years.
If you want to say something than please do what you expect from me/others : be clear about what you mean.
Did I allready mention that I did *multiple* tests ? One thing I did not tell is that they where made months ago, and I do not have an photographic memory. Meaning that there is no way I can tell you *exactly* what I did or had.
Personally I think you got way enough data to work with. From me mentioning diodes without a dummy-load thru 15 mA and later even higher-current dummy-loads.
I have the idea that the diodes (as I mentioned before and in the link I posted) where working *way* below their minimal current, and therefore did not behave as expected.
That is, with my current knowledge, as far as I dare to go in my assumptions.
Be my guest to work out-of-specs. But as far as I am concerned I do wish, especially at first tests, to stay inside so I can be sure that when something does *not* work I did not fry it. Maybe later I would be doing a few tests to see if the different cards keep working with that voltage.
Sorry, but I'll stay with that definition. Using some "hack" that makes the voltage vary wildly with the drawn current and results in a voltage above specs means to me that it "does not work".
Bullshit. in the origional schema (the one I posted the link to) two 1N4148 diodes where all that where needed. How much *can* you do wrong with that (apart from putting them the wrong way in).
I assume that English is not your first language. A lot of posters here are not native English speakers and that can make it harder to tell what they are trying to convey. It also makes it harder to convey what I am saying because there are part of the language I am inclined to use that may not be understood by others, such as the above. I'm not sure if you are being sarcastic, but I am sure a native speaker understands that by "proper language" I mean proper use of the English language.
Ok, It appears that you are not really interested in learning what I have to say, hence the sarcasm. If I am wrong and you really do care, I am saying you don't use the proper terminology and in any one post you only describe part of what you are talking about. I have no way of knowing what you mean when you say things like, "It just would not work." That tells me nothing about *what* you saw wrong.
You posted, "I only measured the voltage over them". The grammar is such that I don't know for sure what this means.
You have posted several times about different configurations and it is hard to tell which info applies to which circuit. Your second post contained a statement that opposes everything I have learned about electronics and physics and I have been trying understand why you said that. In the mean time I have not been able to get you to give me descriptions that I can understand.
If you don't want to discuss this, I understand, but please don't get sarcastic and rude.
Ok, if you don't know the answer to a question, it's ok to say that.
Lots of info, but not enough to understand what applies to what.
There is no minimum current for a diode as such. Initially the voltage v. current is logarithmic and becomes linear at currents near or above the rated current of the diode. This should be shown in the data sheet.
That depends on what you are doing. If I am selling a design, I make sure everything is in spec. If I am building something for a bench test I will build it to work and not worry about the fine details that are not important.
The "wildly" varing voltage is wrong. That is the point I am making. Since I don't understand the details of what you did, I can't say what is wrong. Did you read Jon Kirwan's post where he read from the data sheet that a "0.1V change per 10X in current"? I think you said you used two diodes in series with an LED in parallel with the load at about 10 mA or so. A 50 mA change in load current will be less than
10x and so the voltage change on the diodes will be less than 0.2 volts, within tolerance of the load spec.
Well that is a persuasive argument.
I am sorry, I missed the link to the schematic. I see that your schematic indicates the SD card VCC is at 3.6 volts which is in contradiction to what you say above, "I do wish, especially at first tests, to stay inside so I can be sure that when something does *not* work I did not fry it." You can do as you wish. I have trouble following what you have and haven't done is all I am saying.
You said in one of your posts you said, "In that case the larger current-draw (1mA -> 30~50 mA) by the card ment so much voltage-drop over the resistor (in series with the diode//Card) that nothing was left to work with." That means you were using a resistor with too large a value, hence my statement about not having the correct parts in your parts bin.
BTW, the way you quote at the end of your post the entire message you are replying to makes it hard to be sure your entire message is read.
I'm not trying to argue with you. I am trying to understand. If this is getting you upset, I'll stop discussing this now. It's up to you if you want to continue a proper discussion or not.
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