Talk:LM317

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Voltage regulator section equation makes no sense and is ambiguous[edit]

See inline comments. — Preceding unsigned comment added by 2601:441:4D80:93F0:F5B8:D325:A399:BE75 (talk) 01:42, 10 March 2021 (UTC)[reply]

History[edit]

Is it known when the first LM317 came out ? The design seems to be quite old. --88.156.234.210 20:47, 7 August 2007 (UTC)[reply]

Good article![edit]

I just wanted to say I found this article useful. Plugin solution for a constant current source. Electron9 16:11, 3 October 2007 (UTC)[reply]

Bob Pease not the designer of the LM317[edit]

I recieved email from Bob Pease telling me he was not the designer of the LM317 and said he wanted that changed. —Preceding unsigned comment added by Constant314 (talk • contribs) 16:34, 29 November 2010 (UTC)[reply]


email from Bob Pease " I designed the LM331 and LM337. Bob Dobkin designed the LM317." Constant314 (talk) 17:01, 29 November 2010 (UTC)[reply]

Expansion[edit]

I've expanded the article a little and cited the original patent for the LM317. Does anyone have a decent reference stating that the LM317 is the most popular variable voltreg? I couldn't find one, so for now I've stuck a citation needed flag on it. 86.14.89.253 (talk) 23:25, 10 June 2011 (UTC)[reply]

thanks to wiki... — Preceding unsigned comment added by 122.172.249.221 (talk) 10:27, 10 December 2011 (UTC)[reply]

Photo[edit]

I suggest replacing the photo in the article with a different one, in which the 317 is mounted on a printed circuit board, as it is normally done.Michael9422 (talk) 14:11, 14 May 2013 (UTC)[reply]

Can you provide a reference that defines the normal use of the LM317 as being board-mounted? It would also be good to explain why the device is available in TO-220 packaging, which is designed to be mounted to a heat sink. The good thing about Wikipedia, though, is that a single article can have multiple pictures. -- Mikeblas (talk) 17:11, 29 June 2013 (UTC)[reply]
I do not have a reference. However, I did a search on ebay for 'LM317', and I notice that all of the 317s for sale as part of a regulator (with the 317 in a TO-220 package) are mounted on circuit boards. I believe that the TO-220 package has 0.1-inch pin spacing for that purpose. Also the 317 is available in a TO-3 package, which is intended for chasis mount.Michael9422 (talk) 20:29, 24 November 2013 (UTC)[reply]

External links modified[edit]

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Incorrect interpretation of Vref[edit]

From a recent edit 781399611 by KorgBoy, which changes Voltage regulator part of article from:

Vout = Vref (1 + RL/RH)

Note that Vref is the difference in voltage between the OUT pin and the ADJ pin. Vref is typically 1.25 V during normal operation.

into following:

Vout = Vref (1 + RL/RH)

Note that Vref is the voltage of the ADJ pin itself. Vref is typically 1.25 V during normal operation.

The change seems to be an error, as it actually disagrees with a common usage of LM317- which comprises of a voltage divider to lift the potiential of ADJ pin. The statement also contradicts with Texas Instrument's LM317 datasheet referenced in the article (page 10) which diagram clearly shows that Vref is a difference of Vout and Vadj.

Also, consider this circuit: 

             IN +-------+ OUT
   7.5 V -------| LM317 |---------o Vout
                +-------+         |
                    | ADJ        [ ] Rload
                    |            [ ] 56 ohm
                    |             |
     0 V -----------+-------------o 0 V

The regulator is operating perfectly within specification range: Vout is ~1.2 V as Vadj is driven to 0 V (I tested this with a real LM317). This shows that statement which said Vadj = Vref = 1.25 V is false.

I have marked the statement as disputed--discuss. Unless anyone can provide citations that say otherwise, I will eventually revert the original edit. -- Nvtj (talk) 07:32, 21 May 2017 (UTC)[reply]


Thanks Nvtj. I just reverted what I changed back to the original. If you go through the history, you'll find that it was me that put in the original comments. When I came in recently, I had a think about it, and didn't seem right. But after checking things out, the difference between Vout and Vadj is really meant to be equal to 1.25 V. KorgBoy (talk) 08:02, 27 May 2017 (UTC)[reply]

"the device is conceptually an op amp..."[edit]

is it just me or is this bit (and the explanation that follows it) a bit misleading? First, the equation is different for a real non-inverting opamp amplifier (the feedback resistor is in the numerator), and second, an opamp does not work by "adjusting (...) the voltage of the output pin to be a fixed amount (!), the reference voltage, above that of the adjustment pin" [=inverting input in this analogy], it adjusts the current through the feedback resistor to minimize Vdiff between both inputs, in other words both resistors carry the same current and the output voltage is Vout=Vin*(1+Rf/R1), thus the output is Vout-Vin=Vin*(Rf/R1) above (either) input. 78.53.240.75 (talk) 23:32, 28 August 2017 (UTC)[reply]

Voltage follower
Voltage follower boosted by transistor, also can be seen as the "ideal transistor" without a base voltage drop on the input signal
I agree. One doesn't need to expound on the LM317 output stage being "conceptually an op amp" when it is actually just an amplifier with feedback. Blooteuth (talk) 13:25, 29 August 2017 (UTC)[reply]
A servo loop is coupling the OP amp output to its negative input. The voltage follower is an OP amp with output direct fed into the negative input. It is also the basic circuit of linear voltage regulators. The data sheets of LM317 draw such circuits to make engineers understand how the device works. Such diagrams not not really differ for the real internal circuit. Maybe to save transistors or compensate some unwanted effects, the real circuit differs for the published diagram. --Hans Haase (有问题吗) 13:01, 1 September 2017 (UTC)[reply]
Reviewing the English article of the op amp, there no article about the voltage follower. The German version has sections and articles about, click the pictures, see where used. Limiting current and several other properties are not covered by the simple voltage follower. The external transistors do not exactly rebuilt the op amp non-inverting amplifier, due different circuit and other reference potential. Note the impedance of the ADJ terminal of the LM317 is not the driect input of an op amp. --Hans Haase (有问题吗) 13:19, 1 September 2017 (UTC)[reply]

Forward voltage drop VF[edit]

I might be mistaken, but if someone asked me what the forward voltage drop of a linear regulator would be, I'd say it would be the voltage across its IN and OUT pins. But the calculation assumes the forward voltage drop is the voltage across the load (this, by the way, is in the discussion of the constant current mode of operation). It confused me for a moment, is it correctly used here and am I just assuming the wrong definition? If not, the calculation should be PMAX / VF = 0.98 / 3.6 = 272 mA. Digital Brains (talk) 16:03, 9 March 2019 (UTC)[reply]

Packages, schematics, stuff[edit]

The thermal resistance calculations seem pretty arbitrary and somewhat irrelevant by their specificity. Also, the thermal resistance figures are not inherent to the IC, which the section might be implying. Some discussion of the packages would be an improvement, methinks. I think it is general poor design practice to put the indicator after the current shunt as done in the picture for the current regulator. Granted, it will not make much difference with the forward voltage of modern green LEDs, but if an indicator is truly needed I think on the output pin is a more fitting location. The dropout voltage of the LM317 goes to over 2v at 1A, so indication functionality is not really impaired. There are a great many wonderful application circuits for this IC that the article only mentions in one listing sentence. But maybe detailed explanations belong only in the datasheets and app notes. On terminology, the current through the adjust pin isn't really "quiescent current," I think. That would refer to the couple mA that goes out the output pin. On fixed voltage regulators, Iq exits the "ground" pin so they don't need external sinking on the output, but here that would be a problem as the article explicates to some degree. Maybe mention of the LM317HV variant is also warranted. Someday, especially if my ideas are validated, I hope to help give this IC the Wikipedia page it deserves. But that's hardly related. 1N914 (talk) 02:36, 31 December 2020 (UTC)[reply]

Obsolete?[edit]

Now the LM317 seems not in production anymore? --217.6.200.58 (talk) 07:02, 1 March 2023 (UTC)[reply]

That isn't true. • Sbmeirow • Talk • 02:24, 2 March 2023 (UTC)[reply]
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