15V to 12V Adaptor

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KSS
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Re: 15V to 12V Adaptor

Post by KSS » Mon Sep 14, 2020 1:00 pm

neil.johnson wrote:
Mon Sep 14, 2020 8:25 am
TI LM317: https://www.ti.com/lit/ds/symlink/lm317.pdf
8.4.2 Operation With Low Input Voltage
The device requires up to 3-V headroom (VI–VO) to operate in regulation. The device may dropout and OUTPUT voltage will be INPUT voltage minus dropout voltage with less headroom.
I suspect the author meant (and is clear from the rest of that paragraph) that the device requires a minimum 3-V headroom. So you're saying TI are making false statements?
No. I'm saying you missed the two words I underlined. Up to. As in from something less than UP TO 3V. As shown on the graphs of several DS.
ST LM317: https://www.st.com/resource/en/datasheet/lm317.pdf
Figure 3 shows that at 1A load the LM317 requires a voltage differential of 3V (by eye), dropping to around 2.5V at minimum load. So is ST also making false statements?
ST is speaking about their device, I covered that aready in my reply. I didn't say all DS were the same. In fact, I said the opposite. Suely you already know this as does anyone who lived through the development of TTL and CMOS with all the differences that caught the collective 'us' up unexpectedly. and apparently still do catch some people unexpectedly. ;)
ON: https://www.onsemi.com/pub/Collateral/LM317-D.PDF
Figure 10 shows that for 1A load the dropout voltage is a smidge under 2V at 50'C silicon temperature, rising to just above 2.0V at room temp (less likely scenario once it starts passing current). Nice plot, but what does it really show?
It shows what you're trying so hard to ignore and save face about. That the device does *not* require a 3V drop.
Fairchild: https://neurophysics.ucsd.edu/lab/LM317.pdf
Figure 3 shows that, again for 1A load, you need a minimum headroom of around 2.3V. At full rated current it is more like 2.5V, but these graphs are rather a guide than law (how many devices did they test? across how many batches? what's the distribution? etc)
So when they agree with you, they're good examples, like the ST above. But when they don't, you go after them is sideways? "Pay no attention to the man behind the curtain"? These graphs are -according to you now- only a "guide" but the spec which has *no* minimum value -only showing a *test* voltage, is gospel enough fo ryou to keep figthing for your false belief? Test voltage spec which is of course common in DS -and often supported by plots-graphs. They need to let us know the parameters around which their testing was done. Can't you just admit you were -at least partially- wrong?
In almost all of these datasheets the test conditions in the Electrical Characteristics tables quote the Vo-Vi as between 3V and 40V.
Yes,. That's what I said. But then the ones which *do* go further SHOW that 3V is *not* a minimum. Again, I would think with all your expertise you'd be familiar with copied and selectively edited and shortened 'shared' DS. Bob Pease and Jim Williams cautioned us about that over and over again. Closer to the synth world so did Serge and many others in early Electronotes. Especially WRT Norton amps and OTAs DS.
What that is saying is that these are the ranges of operation that the device is guaranteed to perform over. If you step outside of that range then you're on your own. And what that means is: it may work for you, it may also work for your best buddy, but if you go into production with a circuit that operates outside of those parameters and you start having products fail due to marginal parts, if you then go crying to the manufacturer of the particular LM317 (or whatever) part you are using the Apps Engineer will simply point out you violated the rules so the parts are behaving as advertised and you're on your own. Or, if you were sensible and involved the Apps Engineer in your design before going into production they would simply request you increase the input voltage or change your design (e.g., LDO regulator).
That's a whole lot of words which *are* mostlyv -if not fully- true but which have NO BEARING ON THE PRESENT DISCUSSION. Because the DS in the present discussion DO NOT limit themselves to 3V. Maybe ST does. i didn't read it. Taking your word for that one. The DS in THIS discussion give graphs which show that the dropout is variable and show us how the various parameters we'd be concerned about change with different choices we'd make. Like I already said. And you just repeated above. The problem -for your argument- is your words "if you step outside of that range" do. not. apply. Because 3V is not an absolute minimum value for the device.
And by production, I also mean releasing a board for other DIYers to make. They will buy or make the board, they will buy the parts, they will spend time putting it all together.
I forget what kind of false argument your words above are called? Straw dog? Red herring? No. But there's a name for that kind of wordy truth spoken as if it applies.. misdirection?
I'll vouch for the single module design. Probably the larger one too. But it 'might' be well to put a note for maximum draw on that one. Again you've given nothing but more more 'sideways' words to put us off the fact that your first statement is more often than not as false as I said it was -accounting for the ST DS which according to your report does agree with your initial assertion.

it's funny to me that it's ST, as I've had more problems with that brand -along this exact type of difference- over the decades than any other. They always seem to be just a little different than nearly everyone else. Of course that's TOTALLY anecdotal, and may only apply to my personal experience. But since it does, it's funny to me that it's ST. When they were still SGS Thomson I didn't have the same experience as after they became ST. *I too can use a lot of words that don't really apply to the discussion at hand!" And a search here and Electro-music will show mumerous examples of ST devices not working in certain synth circuits. Of course that's also true for some other mfrs.
But, heh, good luck to the OP, looks like he's having fun.
Harald doesn't need 'luck'. From what I've observed -over several years now- Harald is a careful and gracious provider of well-engineered, robust and useful modules. Moreso than many you could choose to go after the way you did this design.
I'm signing off, have too many projects needing attention as it is ;)
That's probably a good idea.
Treat utility modules as stars instead of backup singers.

Treat power supplies like Rockstars instead of roadies!

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Re: 15V to 12V Adaptor

Post by socom93 » Sat Sep 19, 2020 5:48 am

Haralds:Werk wrote:
Thu Sep 10, 2020 7:56 am
Here is the bigger brother from the single adaptor above. The documentation and the Gerber files for download can be found in my website.




15V_2_12V_mult_top.JPG

15V_2_12V_095_mult_schematic.png

15V_2_12V_mult_front.JPG
Really nice board !
Have read all the comments and haven't anything to had on the LDOs subject.

Just have a small question since i don't know much on the +-15V standard. How much current can handle the 3 points connector ?

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Re: 15V to 12V Adaptor

Post by KSS » Sat Sep 19, 2020 8:04 am

The typical 317 and 337 regulators have a maximum output of 1.5A. In this -bigger- design, you will probably want to draw less than that amount.
I'll leave it to Harald to provide or suggest the actual amount of current draw his multi module design supports.

In Harald's smaller single module design, you definitely will want to draw much less current than the maximum the 317-337 supports. As posts in the thread show, there's more to the answer than just the specs for a single component.

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Re: 15V to 12V Adaptor

Post by Haralds:Werk » Sat Sep 19, 2020 9:21 am

socom93 wrote:
Sat Sep 19, 2020 5:48 am
Just have a small question since i don't know much on the +-15V standard. How much current can handle the 3 points connector ?
There is no +/-15V standard. Those three pin connectors I use for the PSU are rated 2.5A/250V. You can get them from many sources and with different pin counts. I use them in many designs from 2 pins up to 10 pins.
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Re: 15V to 12V Adaptor

Post by Haralds:Werk » Sat Sep 19, 2020 9:26 am

KSS wrote:
Sat Sep 19, 2020 8:04 am
The typical 317 and 337 regulators have a maximum output of 1.5A. In this -bigger- design, you will probably want to draw less than that amount.
I'll leave it to Harald to provide or suggest the actual amount of current draw his multi module design supports.

In Harald's smaller single module design, you definitely will want to draw much less current than the maximum the 317-337 supports. As posts in the thread show, there's more to the answer than just the specs for a single component.
There should be no difference in the load between the smaller and the bigger one. If you exceed 200mA on either one you'll need heatsinks. I'll do some load measurements and come back here.
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Re: 15V to 12V Adaptor

Post by Haralds:Werk » Sun Sep 20, 2020 9:37 am

This adaptor was tested with a load of 1A each rail. It is tested working properly down to an input voltage of 14,5V with an 1A load on each rail. So it should work fine in every 15V system. With a safety margin of 0.5V.

Here are some figures:

LM337
With 500mA load the output voltage degrades at 14V input.
With 800mA load the output voltage degrades at 14,1V input
With 1000mA load the output degrades at 14,5V input

LM317
With 500mA load the output voltage degrades at 13,9V input.
With 800mA load the output voltage degrades at 13,9V input
With 1000mA load the output degrades at 14,2V input

This figures may vary depending on the brand.
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Re: 15V to 12V Adaptor

Post by KSS » Sun Sep 20, 2020 10:10 am

:tu:

What brand are yours?

--------------
Edit- assume these were short tests?
As you said above, Heatsinks are going to be needed for larger current draws over long periods of time.

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Re: 15V to 12V Adaptor

Post by Haralds:Werk » Sun Sep 20, 2020 1:22 pm

KSS wrote:
Sun Sep 20, 2020 10:10 am
:tu:

What brand are yours?

--------------
Edit- assume these were short tests?
As you said above, Heatsinks are going to be needed for larger current draws over long periods of time.
LM337. Fairchild
LM317 ST
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Re: 15V to 12V Adaptor

Post by Haralds:Werk » Sun Sep 20, 2020 1:31 pm

KSS wrote:
Sun Sep 20, 2020 10:10 am
:tu:

What brand are yours?

--------------
Edit- assume these were short tests?
As you said above, Heatsinks are going to be needed for larger current draws over long periods of time.
Yes. The measurements lasted about 10 minutes. I have used small heat sinks. But I have used them in my synth for many hours now without any problem. I can do a longer test next week.
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Re: 15V to 12V Adaptor

Post by KSS » Sun Sep 20, 2020 9:46 pm

Thank you Harald.

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