dual LM317 VV

[webbcm127]

first off thanks to the creater of the poor vari if it wasnt for his diagrams i wouldve been lost!
with that said here is a pic of my parallel'ed LM317 VV

it ranges from 1.2v - 7.4v
im happy with it and the only reason i used the lm317 is because thats all rat shack had, it does work nicely though and doesnt overheat, however there was a bit of trial and error to get it right, let me know what you think!-))

 

[AzPlumber]

Nice and clean looking.

Been doing a little playing around with dual regs myself. Did you use just one pot for both regs? Any idea if both regulators are sharing the load?

 

[webbcm127]

Yeah 1 pot for both and I pretty much soldered them directly together. I'm fairly certain that both are sharing the load, not 100% though but after 2 days of use and no issues I'm not complaining.

 

[o4_srt]

From what I remember, the lm317 is rated to 1.5 amps as long as the voltage differential is less than 10 volts. I've successfully used 1 lm317 with a heat sink for 5v operation.

I did toss around building a dual reg model, but was told it wasn't a worthwhile project from an engineer.

Either way, good to see someone successfully implement it.

 

[raceengine]

nicely done webbcm127.

may sound noob but how does running parallel'ed LM317 VV works?
can anyone chime in? can it put out more amps than rated?

 

[webbcm127]

nicely done webbcm127.

may sound noob but how does running parallel'ed LM317 VV works?
can anyone chime in? can it put out more amps than rated?

Yes it basically doubles the amps +\- I'm at about 3.5-4

 

[o4_srt]

nicely done webbcm127.

may sound noob but how does running parallel'ed LM317 VV works?
can anyone chime in? can it put out more amps than rated?

Theoretically, it should double the available current. However, it's difficult to evenly balance both regulators so they are sharing the load evenly (which is ideal) due to manufacturing tolerances.

 

[webbcm127]

Theoretically, it should double the available current. However, it's difficult to evenly balance both regulators so they are sharing the load evenly (which is ideal) due to manufacturing tolerances.

Very true, but even if it's not sharing equally it's damn close lol

 

[raceengine]

Can I have a look see inside the case? Very interesting stuff

 

[webbcm127]

Can I have a look see inside the case? Very interesting stuff

Tonight or tomorrow when I get on my comp I'll post some pics of the inside!-))

 

[Rocketman]

Actually I believe even with a slight imbalance the first regulator to reach current LIMIT doesn't shut down and the second would pick up the remainder of the required current. The current limit depends on specific model and production variations.
This would not be a problem other than one running a little hotter that the other. Thermal overload will shut the regulator down until it cools off some. Still a good way to UP the current capability of a single regulator.

Some designs use small, 0.1 ohm matching resistors to balance current some, but we usually don't want series resistance

Good use of "available" parts.

Note: Some people recommend LDO (Low Drop Out) regulators. The maximum output would be a little higher or batteries could be used a little lower in the discharge curve. But in the middle of the operating range, same result as what you have.

 

[o4_srt]

Actually I believe even with a slight imbalance the first regulator to reach current LIMIT doesn't shut down and the second would pick up the remainder of the required current. The current limit depends on specific model and production variations.
This would not be a problem other than one running a little hotter that the other. Thermal overload will shut the regulator down until it cools off some. Still a good way to UP the current capability of a single regulator.

Some designs use small, 0.1 ohm matching resistors to balance current some, but we usually don't want series resistance

Good use of "available" parts.

Note: Some people recommend LDO (Low Drop Out) regulators. The maximum output would be a little higher or batteries could be used a little lower in the discharge curve. But in the middle of the operating range, same result as what you have.

Agreed. You'd have to be putting 66%+ of the current through 1 regulator, at 5v with a dual coil carto, to see current limit, assuming minimum rated specs.

With a standard atty/carto, you have nothing to worry about.

 

[webbcm127]

I've been using a DCC tank at 4.5-5 and 6v and never had it shut down on me!-))

 

[AzPlumber]

I was hoping Rocket would join in. I have been playing around with two and three 317 on a solderless board for a few days and Rocket is right on. One seems to get hotter but I have yet to get one into thermal shut down. The balancing resistors are a challange to set the voltage and would make it difficult to get VV.

 

[o4_srt]

I've been using a DCC tank at 4.5-5 and 6v and never had it shut down on me!-))

Great! Then the regulators are adequately balanced!

Are you using heat sinks?

 

[webbcm127]

Great! Then the regulators are adequately balanced!

Are you using heat sinks?

No I'm not but I'm considering adding em just for the safe side of things and I seem to get nice bat life outta the 14500s too!-))

 

[o4_srt]

No I'm not but I'm considering adding em just for the safe side of things and I seem to get nice bat life outta the 14500s too!-))

Radio shack has TO-220 heat sinks for a few bucks apiece if you need a source.

If you search mouser or digikey, you could probably find a double heat sink that would fit both regulators.

 

[webbcm127]

Well what exactly is the heat sinks made from...I feel as if I could make one lol I don't mind spending a few bucks but if I could I'd have more fun making em!-))

 

[o4_srt]

Well what exactly is the heat sinks made from...I feel as if I could make one lol I don't mind spending a few bucks but if I could I'd have more fun making em!-))

That's the spirit! Aluminum is a popular choice.

You're basically just adding thermal mass to the regulator so it doesn't heat up as quickly. A chunk of aluminum with a small hole tapped in it (you can mount the regulator to the heat sink through the hole in the "tab" of the regulator) works fine, although not the most efficient.

Smear a small amount of thermal grease on the side of the regulator that comes in contact with the heat sink for better performance.

A more efficient heat sink design utilizes fins.

Heat sink from radio shackhttp://m.radioshack.com/radioshack/product/detail.do?itemId=2102857

 

[TomCatt]

eBay heatsinks - 20 for ~$8 - 20x TO220 Heatsink | eBay