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- เผยแพร่เมื่อ 3 ต.ค. 2024
- In the modern world. Most power supplies are switch mode, but there still is a place for the transistor based linear regulators. How do they work and can we make one of our own?
-- Links --
Schematic: sinelab.net/im...
My Website: sinelab.net
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An interesting engineering investigation. Good to see you using the full 3V of headroom. For the typical LM78xx V Regs, most people just use the minimum dropout headroom, say 1.5V. However, a more careful inspection of data sheet reveals that a full 3V enables the V Reg to maximize its ripple rejection. In order to be able to state the component's highest ripple rejection numbers, the manufacturer uses 3V to test the component. Again, look closely at the data sheet, particularly at the notes in fine print. Cheers!
Thanks for watching! It's very important to read the datasheet.
Great video and thank you for the schematic.
Glad the video helped. 👍
Nice video
But the craziest thing about LM317 that it can actually be a switching buck regulator! There is a schematic "Low Cost 3A Switching Regulator" in some datasheet.
I did not know about that! That's actually really interesting, thanks for telling me. :)
Curious if you will do a video on choosing a heat-sink. This is a topic avoided by most channels yet a common question.
Yes, that is a good topic that I will plan to cover.
Nice👍
Can you explain about LDO voltage inside laptops, phones, tvs, many things like that.
What do you need to know that is missing from the video?
A BJT transistor in a TO-66 package is also easily attached to a heat-sink. Or go for a BJT in a TO-3 package!!
I only had TO-92 BJT transistors, so it simply made more sense for me to use the TO-220 mosfet. Choose what you have. :)
PL - Elegancki materiał :> swietnie wytlumaczone dzialane lm317, moze cos o zejsciu ponizej 1,25v?
EN - Elegant material :> well explained action lm317, maybe something about the descent below 1.25v?
usually they simply stop regulating and pass the voltage though with a voltage drop - check the datasheet
You can also create a way to connect the adjust pin to -1.25 volts if you really must go all the way down to 0 volts.
@@SineLab i know, but this ic is like a moltitool ;) curent source etc, please continue ;)
Fun video. But LM317 uses Output Terminal (nor ADJ) to power the negative rail of the OPAMP. We would require a good 'almost' rail to rail OPAMP.
BUT the main issue is, initially when system is powered ON, Transistor is OFF, hence OUTPUT Terminal is FLOATING because of which OPAMP will not be powered and it will not operate. If it doesnt operate, it would continue to 'not work'.
Any idea how that works?
Thanks for watching! The op-amp's negative rail is initially connected to a lower voltage through the load on the output. This can be seen as the minimum 10mA load specified in the datasheet.
@@SineLab Wow. How could I miss that.
So since the current consumed by OPAMP is very very less, the votlage dropped by the load is minimum, essentially passes the Ground to the Output terminal and hense to OPAMP rail. Fabulous thinking and design!
On Normal fixed regulator, the negative rail is connected to ground. Obviously because we on LM317 needs minimum current at Adjust pin so it doesnt load the output voltage divider. But on fixed regulators its not required so a small current may pass through ground.
On LM317 OPAMP Must operate with minimum power supply or else the Minimum Droput voltage must increase. That's the challenge faced for its design.
Anyway thanks for answering, been looking it up on the internet. But almost everyplace people were omitting the power supply lines 😠.
So I would love to know how did you figure it out? Did it clicked automatically or you already knew?
Glad you understand now! I figured it out by looking at the schematic and also running a couple of simulations. The Falstad online simulator is good if you want to try it out as well. :)
nice
what do you sell, bs
you praise the trash market stuff, so you must be a sell-out