15V to 12V Adaptor

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15V to 12V Adaptor

Post by Haralds:Werk » Tue Feb 11, 2020 4:37 am

From time to time I want to integrate a 12V Eurorack module in my 15V banana setup. So I needed a 15V to 12V adaptor. Nothing spectacular. Just from the datasheet.

Specs and features
• Input +/-15V DC (or higher)
• Output +/-12V DC

The documentation and the Gerber files for download can be found in my website.
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Re: 15V to 12V Adaptor

Post by dot matrix madness » Tue Feb 11, 2020 8:17 am

Allright, this allows to fine tune the rail voltages (for more than just one module), but wouldn't a combination of 78L12 and 79L12
voltage regulators be sufficient for most applications?
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Re: 15V to 12V Adaptor

Post by Haralds:Werk » 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
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Re: 15V to 12V Adaptor

Post by Addam » Thu Sep 10, 2020 9:37 am

Thank you for this! :sb: Making one of these on perfboard has been on my to-do list for about 2 years

I'm going to order some PCBs- if anyone in US wants 1 or 2 lemme know.

Edit: I should mention, for trade (ideally) or a couple bucks for shipping.
Last edited by Addam on Sat Sep 12, 2020 12:50 pm, edited 1 time in total.

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Re: 15V to 12V Adaptor

Post by EATyourGUITAR » Sat Sep 12, 2020 11:49 am

What is the license? Can I sell the PCB in my store? I would be happy to offer this for sale in my store if you will allow it. Probably $6 for the small one and $10 for the bigger one.
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Re: 15V to 12V Adaptor

Post by BananaPlug » Sat Sep 12, 2020 12:26 pm

Yes, please make them available. It gladly upgrade from my functional but nasty perf board thing.
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Re: 15V to 12V Adaptor

Post by neil.johnson » Sat Sep 12, 2020 2:49 pm

I would have thought going from 15V down to 12V where you have a nominal 3V difference it would be better to use LDO regulators? The LM337 needs a minimum of 2.5V and the LM317 needs a minimum of 3V differential, which is rather tight on 15V rails and doesn't leave much room for the regulators to do their regulation. It just needs the input voltage to be slightly low and you'll end up with a regulator not regulating. Or it may be fine when you set up in a lightly loaded case, but then adding more modules drops the 15V rails by 100-200mV and you're in trouble.

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Re: 15V to 12V Adaptor

Post by EATyourGUITAR » Sat Sep 12, 2020 3:04 pm

neil.johnson wrote:
Sat Sep 12, 2020 2:49 pm
I would have thought going from 15V down to 12V where you have a nominal 3V difference it would be better to use LDO regulators? The LM337 needs a minimum of 2.5V and the LM317 needs a minimum of 3V differential, which is rather tight on 15V rails and doesn't leave much room for the regulators to do their regulation. It just needs the input voltage to be slightly low and you'll end up with a regulator not regulating. Or it may be fine when you set up in a lightly loaded case, but then adding more modules drops the 15V rails by 100-200mV and you're in trouble.

Neil
this maybe?

pos
LM1085IT-12

neg
LM2990T-12

adjustable versions are also available -adj
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Re: 15V to 12V Adaptor

Post by MikeDB » Sat Sep 12, 2020 8:14 pm

EATyourGUITAR wrote:
Sat Sep 12, 2020 3:04 pm
this maybe?

pos
LM1085IT-12

neg
LM2990T-12

adjustable versions are also available -adj
LM2490 is the usual complement to the LM2990. Both are excellent fairly modern devices with far better performance than the older ones mentioned earlier.
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Re: 15V to 12V Adaptor

Post by EATyourGUITAR » Sat Sep 12, 2020 8:41 pm

this is intentional. the LM1085IT-12 is cheaper with more amps compared to LM2490T. I could not find a negative 12v TO-220 (T code) part that can deliver 3 amps. I think this works out ok though because most digital modules draw more on the +12v side. the total system provides 3A +12v 1A -12v with proper heatsinks or 400mA per rail max without heatsinks.
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Re: 15V to 12V Adaptor

Post by KSS » Sun Sep 13, 2020 5:22 am

@neil.johnson
317's and 337's do fine with nominal 3v drop.
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Re: 15V to 12V Adaptor

Post by neil.johnson » Sun Sep 13, 2020 5:55 am

KSS wrote:
Sun Sep 13, 2020 5:22 am
@neil.johnson
317's and 337's do fine with nominal 3v drop.
Under what conditions? If Vin is a bit low, say 14.5V (e.g., source 7815 on the low side, plus IR drops at 1A load), and the user has set the output to slightly high (say 12.2V), and load is 1A, you only have 2.3V to spare. And then you've stepped outside of the recommended parameters in the datasheet.

It's marginal operation at best, and when there are LDO alternatives available why would you not give the design some healthy margin?

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Re: 15V to 12V Adaptor

Post by KSS » Sun Sep 13, 2020 6:17 am

I fully expected this response. It works. Reliably. Every. Time. I've. Used. It.

That's good enough reason -in my book- to make the post.

Doesn't mean there isn't something else equal or better.

Does mean :tu: to what Harald presents here.
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Re: 15V to 12V Adaptor

Post by Haralds:Werk » Sun Sep 13, 2020 7:35 am

Addam wrote:
Thu Sep 10, 2020 9:37 am
Thank you for this! :sb: Making one of these on perfboard has been on my to-do list for about 2 years

I'm going to order some PCBs- if anyone in US wants 1 or 2 lemme know.

Edit: I should mention, for trade (ideally) or a couple bucks for shipping.
Thanks. I am happy that my PCB's are helpful.
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Re: 15V to 12V Adaptor

Post by Haralds:Werk » Sun Sep 13, 2020 7:41 am

EATyourGUITAR wrote:
Sat Sep 12, 2020 11:49 am
What is the license? Can I sell the PCB in my store? I would be happy to offer this for sale in my store if you will allow it. Probably $6 for the small one and $10 for the bigger one.
I am not sure what to do here. My designs are free for private use in the DIY community and everybody can download the Gerbers from my site and order the PCB's from any manufacturer of his choice. And I have some spares left for most of my projects which I sell on request. I have no business though. Let's discuss this offline.
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Re: 15V to 12V Adaptor

Post by Haralds:Werk » Sun Sep 13, 2020 7:42 am

BananaPlug wrote:
Sat Sep 12, 2020 12:26 pm
Yes, please make them available. It gladly upgrade from my functional but nasty perf board thing.
You can download the Gerber files from my website and order yourself from a manufacturer of your choice. That's the cheapest solution.
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Re: 15V to 12V Adaptor

Post by Haralds:Werk » Sun Sep 13, 2020 8:03 am

neil.johnson wrote:
Sat Sep 12, 2020 2:49 pm
I would have thought going from 15V down to 12V where you have a nominal 3V difference it would be better to use LDO regulators? The LM337 needs a minimum of 2.5V and the LM317 needs a minimum of 3V differential, which is rather tight on 15V rails and doesn't leave much room for the regulators to do their regulation. It just needs the input voltage to be slightly low and you'll end up with a regulator not regulating. Or it may be fine when you set up in a lightly loaded case, but then adding more modules drops the 15V rails by 100-200mV and you're in trouble.

Neil
Thanks Neil. Good point. Those figures are still in the datasheets. That is correct. But in my experience the LM337 and the LM317 you can buy today seems to be already LDO's without mentioning. I have no problems using them in this application. After reading your comment I just made a quick check of my actual build. The load was only 300mA each rail (didn't have enough modules around on the bench). The output voltage was set to 12,2V. I then lowered the input voltage from 15V down in 100mV steps. The output voltage starts to degrade at around 13,5V input voltage. So we can deduce that both regulators work down to 1.5V . That is what you expect from an LDO today. If I find the time I'll repeat the test with a higher load asap.

If anybody has some old regulators at hand, say 20 years old I am interested in the figures off those old regulators. Maybe someone can confirm the switching to LDO architecture without mentioning in the datasheet.
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Re: 15V to 12V Adaptor

Post by Haralds:Werk » Sun Sep 13, 2020 8:13 am

KSS wrote:
Sun Sep 13, 2020 6:17 am
I fully expected this response. It works. Reliably. Every. Time. I've. Used. It.

That's good enough reason -in my book- to make the post.

Doesn't mean there isn't something else equal or better.

Does mean :tu: to what Harald presents here.
Thanks. That's my experience as well. But Neil has a good point. Why not change to newer LDO's? I'll look into that when I need to update the circuitry or when I find that it did nor work under a load of 1A. Have still to check this with 1A. 300mA went fine.
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Re: 15V to 12V Adaptor

Post by MikeDB » Sun Sep 13, 2020 12:41 pm

EATyourGUITAR wrote:
Sat Sep 12, 2020 8:41 pm
this is intentional. the LM1085IT-12 is cheaper with more amps compared to LM2490T. I could not find a negative 12v TO-220 (T code) part that can deliver 3 amps. I think this works out ok though because most digital modules draw more on the +12v side. the total system provides 3A +12v 1A -12v with proper heatsinks or 400mA per rail max without heatsinks.
Ah ok. LT1033 then on negative.
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Re: 15V to 12V Adaptor

Post by EATyourGUITAR » Sun Sep 13, 2020 1:09 pm

I looked at Linear Technically (LT) but I decided to stick to Texas Instruments. LT has a lot of nice parts but generally they are more expensive where I live.
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Re: 15V to 12V Adaptor

Post by dot matrix madness » Mon Sep 14, 2020 3:43 am

Interesting thread guys! I'm I right that the LM1085IT-12 can be implemented the same way
(just caps to ground) as a µA7812 (going down from +15V to +12V) ?
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Re: 15V to 12V Adaptor

Post by neil.johnson » Mon Sep 14, 2020 4:00 am

Pretty much. You might prefer to consider the lower-current parts for a slightly cheaper option. Just make sure you follow the recommendations on output capacitor (aim for 50uF or larger aluminium electrolytic). The 1uF used in this design is too small to ensure stability. A 10uF tant might fit on the PCB.

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Re: 15V to 12V Adaptor

Post by KSS » Mon Sep 14, 2020 5:28 am

neil.johnson wrote:
Sat Sep 12, 2020 2:49 pm
The LM337 needs a minimum of 2.5V and the LM317 needs a minimum of 3V differential, which is rather tight on 15V rails and doesn't leave much room for the regulators to do their regulation.
This -underlined by me- is a false statement. I've known and believed this for quite some time but last night I re-read at least five different mfrs. 317 and 337 datasheets. Threw in the 78XX for good measure.

As I recelled there is no minimum given in the Vin-Vout ratings. What *is* there -in most of the datasheets- is a testing spec. Which shows 3v being used for the testing. That actual minimum entry for Vout-Vin is left blank. Implying there's no minimum. This is true for the National and TI older DS, and is unofficially referenced if you look at things like the 78XX which shows only 2V drop suggested for 5V output.

Finally I came across what I remembered. in a Fairchild DS there is a graph which shows that the 3V "testing voltage" is exactly that, a testing voltage, *Not* a required minimum. For it shows the regulation and ampacity at various Vin-Vout drops down to 1v5. Which is what you'd kinda expect from a Vreg based on a 1v2 reference. And there we can see that the full 1.5A is available at less than 3V at temps under 50c. 1A can be drawn with less than 2V drop. The curve there is U-shaped so it's better if you load it well at that drop.

Then I found another TI DS which had even more graphs. None of which were in oppostiion to what's shared above. All showed graphs at various drops between 1v5 and 3v. Making it quite clear that there is a range and these grapsh show what you compromise or accept by choosing different drops.

Here's the short summary. The way in which Harald is using the Vregs in his design lie well and perfectly within the expected use for the device vacross all mfrs DS I could find. He's not promoting this as a general full case power supply. Only for a single or limited number.

In a more general sense, when you're attempting to draw the most current with the best results, you'd be better off to use at least 3V drop. So Neil's comments shouldn't be completely discounted.
But even a 1A draw with a nominal 2v3 drop is very likely to be fine in nornal synth cases <--SWIDT ;)

Like Neil has -I imagine- I've also long been told that these Vregs require a 3V drop. But a project long ago made me look deeper into this and duplicating that effort last night night -along with empirical evidence from multiple projects since in widespread usage- re-affirms that just because something is widely accepted as truth, doesn't mean it is.
Haralds:Werk wrote:
Sun Sep 13, 2020 8:03 am
But in my experience the LM337 and the LM317 you can buy today seems to be already LDO's without mentioning.
Not really LDO's but they've always been based on a 1v2 reference. And the 3V drop as a *requirement* is something I've never seen outside it being listed as a "test" spec in the datasheets. Well, i've also seen the DIY and magazine articles over the last 40 years saying three volts is a must.
And as general advice it's worth noting. But we need to dig deeper if we want all the information.
The output voltage starts to degrade at around 13,5V input voltage. So we can deduce that both regulators work down to 1.5V
Yes. Your result is completely in line with the datasheets.
If anybody has some old regulators at hand, say 20 years old I am interested in the figures off those old regulators. Maybe someone can confirm the switching to LDO architecture without mentioning in the datasheet.
As before said, I don't think anything ever shifted, circuit-wise. Just a result from a widely repeated generalization of a typical good practice becoming accepted "fact" instead of accurately reflecting the always underlying truth. Certainly we've seen plenty of axamples of that happening in both electronics and synths!

Yet another example of why I always say to read more than one datasheet, and especially to read the DS which EXACTLY comforms to *your* device.

And while in this case most of what I read *was* online, there've still been plenty of times when that is no longer the -easy- case. Meaning it might be out there somewhere but finding it may prove difficult if not impossible.

Trusting that the information you need wil always be online is a mistake. Expecially if youre pursuing older designs. Save that stuff -when you find it- locally!
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Re: 15V to 12V Adaptor

Post by KSS » Mon Sep 14, 2020 5:38 am

neil.johnson wrote:
Mon Sep 14, 2020 4:00 am
Just make sure you follow the recommendations on output capacitor (aim for 50uF or larger aluminium electrolytic). The 1uF used in this design is too small to ensure stability. A 10uF tant might fit on the PCB.
A 1uF tant already equates to a 25uF electrolytic. This was also mentioend a few times in what I read last night.

All too often people who don't know the difference -or who have heard and believed that "all tants are bad", will try to replace tants like this with equal value elcaps. Which then begats yet another instance shared online which misses the important point. Because the reporting person doesn't know there *is* a point missing. After a few repeats of thisk, the groupthink takes over and another falsity takes hold.
------------
Important point. I did NOT read the DS for the part in play here. My comments are made as a general reference and *may* not apply to this specific device. They *do* apply to many Vregs with tants specified precisely FOR their distinct and unique performance.
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Re: 15V to 12V Adaptor

Post by neil.johnson » Mon Sep 14, 2020 8:25 am

KSS wrote:
Mon Sep 14, 2020 5:28 am
neil.johnson wrote:
Sat Sep 12, 2020 2:49 pm
The LM337 needs a minimum of 2.5V and the LM317 needs a minimum of 3V differential, which is rather tight on 15V rails and doesn't leave much room for the regulators to do their regulation.
This -underlined by me- is a false statement. I've known and believed this for quite some time but last night I re-read at least five different mfrs. 317 and 337 datasheets. Threw in the 78XX for good measure.
Oh, let me check...

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?

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?

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?

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)

In almost all of these datasheets the test conditions in the Electrical Characteristics tables quote the Vo-Vi as between 3V and 40V.

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).

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.

But, heh, good luck to the OP, looks like he's having fun. I'm signing off, have too many projects needing attention as it is ;)

Cheers,
Neil
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