Linear Voltage Regulator - LM317L - Simply Put

Linear voltage regulation takes a higher and possibly unsteady DC voltage and converts some to heat to generate a lower, regulated DC voltage. LM317L is a veteran of this industry.

[jeffblake]

You say you're talking to hobbyists. Im at Uni doing Electrical Eng and you're helping me more than my lecturers. Thanks for your videos.

[Flyrip]

Again right on the spot for a learning hobbyist like me. Your way of getting very good information in a exceptional way is so awesome. Big big thanks!!!

[TurboWindex]

Thanks for spending some of your time to make these videos. Very useful stuff and it is all explained very clearly. I also loved the fact that the content was not only shown on a white board but also super compact with all the cuts in the video, not wasting anyone time, legend. You should make some more if you have any extra time, you never know when the Youtube gods will shine on your channel. Just add a few customized thumbnails and you're good to go. Take care !

[retronexusnet]

Just one of the best electronics guys on YT. Please make more content. you deserve more viewers!

[chrisromeo]

Hi Simply Put,


This video was insanely helpful. I cannot thank you enough. I've just discovered your channel, and I don't know how I've gone so long without knowing about it. I'm a senior-year electrical engineering undergraduate who has watched more than his fair share of YT videos for help with various analog circuit analysis and digital design concepts, yet Google has NEVER once recommended your channel to me when I needed help with tons of different classes. I don't understand how I wasn't subscribed to you years ago. It's amazing how I can do so well at a university studying electronics and circuit theory for 3+ years, yet I'm still lacking so much of the basic, practical knowledge they don't teach us on how to actually make real things that do stuff without blowing up. I've recently started binging all of the videos on your channel, slowly filling the cracks of my university-level education with the extremely-applicable, invaluable knowledge you have shared with the YT community. Your videos are exactly what I've been looking for to explain simple electronics concepts and how to use them in the exact way I need them to be explained, and I've already shared your channel with several of my electrical undergrad friends.


Now that that's out of the way, I do have one question. After watching this video along with the video on decoupling capacitors, I understand that the first (leftmost/large) decoupling cap is meant to compensate for (low-frequency) dips in the power supply voltage, and to supply voltage/power to the regulator when the power supply falls for a short period of time. I know that it smooths out the power supply voltage so that a nice, pretty-much-constant input voltage is supplied to the regulator THAT IS HIGH ENOUGH FOR IT TO WORK PROPERLY. However, if your input voltage is, say, 7V (for the headroom), and you are regulating it down to 5V, but your power supply only momentarily drops to maybe 6V or 5.5V, wouldn't you technically not need the first decoupling capacitor? Even if the power supply voltage falters a bit, but it is still sufficiently high enough to be regulated down to 5V, would a 6V dip (still >5V) not still be regulated down to 5V in the same way 7V would be? And the dip wouldn't have any effect? So, I guess my question is: Is the first decoupling cap for smoothing out the input voltage and supplying the necessary voltage to the regulator ONLY WHEN IT DROPS BELOW THE VOLTAGE YOU'RE TRYING TO REGULATE TO?


Same thing for the second (rightmost/small) decoupling capacitor. I know that that cap is for filtering out the (high-frequency) ripple noise in the output voltage -- you explained how it only affects high frequencies extremely well in the decoupling cap video, BTW. However, if the regulator regulates all dips in the input voltage that are still greater than 5V down to 5V (like I am guessing it does), would those ripples then NOT show up in the output voltage? Even if they were high frequency drops, would they still not be regulated down to a flat 5V just like all other input voltages above 5V would be? (e.g., the same way the constant 7V you are trying to supply it would be)


I am probably answering my own question in saying that this device linearly regulates the voltage (hence the name), so any low-frequency dropouts OR high-frequency ripple noise in the input voltage would propagate through to the output, just linearly-scaled down to 5V but still dipping/rippling proportionally. In that case, you would definitely need both capacitors, and the first decoupling capacitor would not ONLY be used for when the input voltage drops below the voltage you are regulating to (5V), but in ANY case when the power supply dips at all (whether to a voltage below 5V or not). And that would make sense EXCEPT for the fact that the output voltage you're trying to get does NOT depend on the actual value of the input voltage -- it just depends on the resistor value(s) you choose, and the fact that the input voltage you supply is sufficiently higher then that desired output voltage. If the regulator DID depend on input voltage, then you would need to have a specific input voltage to get the desired 5V at the output; i.e., it wouldn't work for any input voltage that is sufficiently high enough.


So which is it -- does the regulator like blanket scale any (sufficient) input voltage down to 5V, including power supply dips and high-frequency noise? So then you wouldn't need the capacitors? Or does it linearly scale down input voltage including any dips and noise, in which case you would need both capacitors? But then the specific output voltage you get would depend on the actual value of input voltage, wouldn't it?


Any clarification to this would be super helpful, so that I can 100% understand this core circuit component. Again, thank you for such amazing, helpful videos.


-- Chris

[nathanw]

This was seriously helpful. 20 views for this video! YT is getting its search algorithms very wrong. Thank you, Simply Put. I have several LM317Ls, and I need a stable 1.5v for an RF circuit. This chip ain't ideal, it seems, but it's what I got, so it'll have to do. You've made it much clearer. From a fellow would-be electronics engineer/ carpet fitter.

[JN-kz]

hello and thanks for all those extremely helpful video :) do you have any idea about the resistor power rating?
I'm having this doubt and i can't find useful informations on the datashieet!

[charlesklein]

YOU HAVE REALLY NICE AUDIO! were did you get your headphones/microphone, they seem really nice. are you related to the "lord of the rings?"