Thermal resistance junction to case is about 2ºC/W max.

No it is not, it is 4ºC/W. I agree that Case to heatsink is about 0.5ºC/W.

That heatsink of 10ºC/W shown is good for 150mA.

No it is not, its thermal resistance is much more at 24.5ºC/W.

The ambient inside the box is unknown but lets calculate with 40ºC. The total thermal resistance outside the box is 29ºC/W so with 2.91W the temperature of the chip is 124.4ºC. The Max allowed chip temperature is 125ºC.

<snip>

 

OK, at this point short of building this project both of you have had your say and nothing can be proven. I have already stated ventilation is a very good idea.

I'm leaving this thread open so beginners can ask questions, but I will moderate discussion as needed.

 

Years ago I built an LM317 variable voltage power supply with the same little heatsink mounted inside the same little box. A minute ago I looked for it but couldn't find it, maybe I left it at my job when I retired.

Sure the LM317 got hot. But My wall-wart that powered it was only 12VDC, I never shorted the output and never used it at less than 5V so it was fine.

 

OK, at this point short of building this project both of you have had your say and nothing can be proven. I have already stated ventilation is a very good idea.

You are right, Bill. There is no point on fuelling this discussion. The important here is to help who needs help.

 

I like the concise presentation "as-is." Information regarding details of operation could easily be provided by follow-up discussion, and I do have a couple of elementry questions myself. For example, what is the 200R trim pot used for since the output is determined by the 1k "VR adj volts?" Also, what does "MKT" stand for? And finally,why are two caps needed to smooth the output? None of these questions need be answered for me to construct and use this circuit, and therefore are unnecessary for its basic presentation. I rate myself as "hopelessly novice" in ability and find the schematic simple and fully adequate. I appreciate the addition of the photographs suggesting parts layout; the author has already spent the time to determine the 'best' layout for a fairly compact arrangement and this saves me a bit of trial-and-error and ultimately some space on my board. PCB layout necessary? Absolutely not! I personally wouldn't waste time making a PCB for a one-up simple project like this one. Finally, I hate YouTube presentations with step-by-step instructions for such a simple project. I like a speedier, more concise presentation than watching someone solder each connection and slowly narrate which end of the capacitor gets soldered first. I usually avoid any project that requires that I watch the YouTube video; time is valuable for me and I surf to the next schematic that can be quickly and easily followed for whatever project interests me. YouTube is fine as a supplement, but please don't present information essential for the project's construction only in that format. Otherwise, you loose me and others like me who prefer speedy, concise presentations.

The addition of a fuse and an inexpensive voltmeter are, in my opinion, necessary 'options.' (Hum, an oxymoron, I believe.) Otherwise, the project stands as presented for my uses. My thanks to the author for sharing his project!

I'm sorry to see this chap from OZ booted off the forum, but I understand that if he was making nasty comments about others and their projects that he might be more disruptive than helpful overall. Is it possible to allow him to initiate threads and only reply to his own original posts? That way he might still contribute without annoying others except those playing in his arena.

[Note to the moderator: I enjoy this forum immensely and add my comments to this old posting primarily as a general commentary regarding design presentation for others' consideration when presenting their own projects.]

 

Welcome to AAC.

One of the worst things that can be done here on AAC after spamming is both flaming and trolling. Neither behavior is permitted here. We are an international forum, we get people who might consider themselves enemies all the time. We have a lot of beginners in electronics show up, so our ToS spells out the types of projects we do not permit.

I like Mr. Jackson. Ultimately I voted for his banning, he was given several chances and yet continued his antisocial behavior. His presentations are top notch however, good for beginners everywhere. A bit of paradox in one person.

The LM317 and its compliment, the LM337, are both excellent for beginners power supplies. There have been many projects presented on how to use them. If you haven't built a simple variable power supply this can get you started.

I have several resources I offer for folks here. AAC offers local albums, attachments, and blogs. To get full use of the resources offered you must have 10 posts, this is because of hit and run poster types.

Basic Bench Top Power Supplies

Bill's Index

The LM317T requires 10ma for it to work correctly, here is another schematic showing the same chip and how it is used.

120Ω for R1 is the largest value of resistor for this chip, though there are flavors of the LM317 that can go up to 240Ω. They handle less wattage though.

 

...For example, what is the 200R trim pot used for since the output is determined by the 1k "VR adj volts?"...

Hello Hichael, and welcome to AAC. The output voltage is both determined by the 1K resistor and by the 200R trimpot. What happens is that the LM317 regulates the voltage on pin 2, limiting it to 1.25V. Now, the 200R trimpot and the 47R resistor in series with the 1K resistor make a voltage divider, but due to the regulating action on pin 2, the voltage drop on the 1K resistor is always 1.25V. Thus, the 200R pot are used to effectively the output voltage so the voltage drop on the 1K resistor is always the same.

...Also, what does "MKT" stand for?...

Now, referring to your second question, MKT stands for metalised plastic polyester, a type of capacitor.

...And finally,why are two caps needed to smooth the output?...

The 10uf electrolytic stabilizes the regulator on the load side, by suppressing instabilities caused by short peaks of demanded current. The 100nF polyester does the same, but it is more effective against high frequency oscillations. Therefore the 10uF is used for its relatively big capacitance and the 100nF capacitor compensates the "slower action" of the 10uF electrolytic.

 

Try looking on the top of his post.

I've been regularly rejecting those that are only You Tube videos. You may complain, but it meets all criteria stated.

It is also an excellent project for beginners.

I would have loved to know the purpose of the diode across the regulator IC

 

I would have loved to know the purpose of the diode across the regulator IC

The datasheet for the LM317 tells you about the diode.