Where did you personally use or see LM317 applied to?

Thread Starter

q12x

Joined Sep 25, 2015
1,734
But I designed my own. ( switching regulator )
If you can, give me your design for your switching regulator to replicate it here. Also mention what power (1W,5W,10W) resistors you used in yours (if any).
 

dl324

Joined Mar 30, 2015
16,996
The LOAD current is the motor current and was 1A at 1.5V = 1.5W only on the motor, when I test it directly connected to the variable PSU - I read the Amp on its screen.
With proper heat sinking, LM317 should be able to provide 1A. Have you tried a larger heat sink? Do you have thermal paste between the regulator and heat sink?
 

Thread Starter

q12x

Joined Sep 25, 2015
1,734
With proper heat sinking, LM317 should be able to provide 1A. Have you tried a larger heat sink? Do you have thermal paste between the regulator and heat sink?
NO and NO. I will try them now...
But I will change the breadboard circuit to a very simple cct like this:
Voltage Regulator with 1.5v output.jpg
minus the diodes.
This cct is without PNP tr for additional current !
To this cct I will add a bigger heatsink and also thermal paste as you say.
 

crutschow

Joined Mar 14, 2008
34,682
Even if your source has a very dubious explanation,
Seems clear to me.
Why do you think it's dubious?
This means, that 2.45W can be disipated if Im using 3xLM317 in paralel ?
Yes, in theory.
But since each will have a slightly different output voltage due to tolerance it their reference, you will need to add small balancing resistor at each output, so one doesn't hog the load.
You will have to determine the optimum resistor value by test.

Likely better just to use one and add a small heat-sink.
 

Thread Starter

q12x

Joined Sep 25, 2015
1,734
With proper heat sinking, LM317 should be able to provide 1A.
I put a bigger heatsink as you mentioned using the above basic cct:
1704848112694.jpeg
I got a 650mA (instead of 700mA as with earlier experiment) on my PSU readout, and LM317 was not hot anymore. Warm like 5dgr over the ambient but not hot. This is good news ! But the size is enormous of that heatsink ! I dont like it.
I still didn't get 1A on the Amp meter !
I had a wonderful idea to actually measure the motor coil and it give me 0.6R (or 0.5R because was fluctuating a bit). You can simulate my motor coil using 2x1R in // to give you 0.5R and try my cct I have and see if you get the same results as I have here, and after that see if you can rise it up to 1A over this load.
Thank you !
 

dendad

Joined Feb 20, 2016
4,494
I use them in quite a few designs too, unless a switch mode reg is called for.
But one interesting application, at least I think so, was to make a constant current power supply for some UV LEDs that are installed in an old microwave oven, converting it to a UV exposure box for my son's resin 3D printer. Microwave ovens are easily picked up for nothing and supply a case with interlock, timer and turntable.
https://www.thingiverse.com/thing:5263579
1704850695101.png
(My son spray painted the front glass to make it safer after this picture was taken)

In fact, I actually used an LM337, not LM317 as I have lots of them too, but an LM317 would well work too with the appropriate circuit configuration.
1704850919537.png
LM317 circuit....
1704850894057.png
 

SamR

Joined Mar 19, 2019
5,059
There is a 5-7A variant in the LM138/LM338 that comes in TO-3 and TO-220 packages. I haven't used any TO-3 regulators since the late 70's but they are still out there. I'd use aluminum chassis project boxes with a ventilated steel cover to hold the circuit and XFMR and mount the TO-3 on the outside of the aluminum chassis which became the heat sink. Didn't ever need that much amperage but it was what we had available back then from the local electronics supply house. Still have some in the parts drawers...
 

Thread Starter

q12x

Joined Sep 25, 2015
1,734
In days of old I designed CRT monitors and TV sets. I have used the LM317 to make 6.3V filament voltage. It is hard to get a LM7806.
And how many Amp was drawing the filament? What was the Wattage on the filament LOAD and then on the LM317? Approximate if you dont remember exact values. Thanks. I want to make an idea the power LM317 it is usually used.
 

Thread Starter

q12x

Joined Sep 25, 2015
1,734
Below is the LTspice sim of MrChips circuit in Post #2:
A small battery is emulated by the large capacitor CBattery, starting at the discharged voltage of 11V.
The value of Rs determines the charging current.
Can you simulate for me the Power over LM317 ? I imagine it might be a few mW like 100mW or lower. Am I right?
 

Thread Starter

q12x

Joined Sep 25, 2015
1,734
In fact, I actually used an LM337, not LM317 as I have lots of them too, but an LM317 would well work too with the appropriate circuit configuration.
1704859822841.png
1704860054451.png
So, you are driving a couple of LEDs with it, right? Somewhere around 50 to 100mA in total?
Ive seen this idea of driving LEDs with LM317 as well. But with the classic cct that is using a voltage divider on ADJust pin.
Your cct is a Constant Current circuit. I must try it with some normal leds, not UV as you did there.
I find it in the datasheet, but instead of LEDs is a charger. But is the same Constant Current idea.

1704860024811.jpeg
-A few questions:
What was the input voltage at Vin?
What was the total voltage and amperage over the LOAD (your UV Leds)?
What was the Power dissipation over your LM337?
Thanks.
 
Last edited:

SamR

Joined Mar 19, 2019
5,059
Filament transformers typically do not have a lot of VA's. For that you might look for a 120/240VAC to 24VAC center tapped secondary XFMR and the higher the VA the higher the price.
 

joeyd999

Joined Jun 6, 2011
5,358
Long ago, I designed a high performance, low noise deuterium lamp driver for an HPLC (high pressure liquid chromatography) detector using an LM317 as a floating current source with 100V compliance.

It shaved about 25 components off the original design (using high voltage precision op amps) and performed better.
 

dendad

Joined Feb 20, 2016
4,494
The reg is connected as a constant current source, not a voltage regulator. It keeps the voltage across the "load" R1 constant so keeping the current constant. If for a test, if you were to short one (or all) of the LEDs out, the current will remain the same. LEDs run best from a current source. If the LEDs were to be run from a constant voltage source, and a series resistor used to limit the current, and one LED was shorted, then the current through the other LEDs would rise, maybe destroying them.
Also, a constant current source keeps the current stable as the LED temperature changes.
The current is set by R1, so I = 1.25V/2R2 = around 570 mA. If you try other LEDs, adjust R1 to suit the required LED current.
 

dendad

Joined Feb 20, 2016
4,494
Another use I have seen for the LM317 is to have a couple in series. The first wired as a constant current source with a variable resistor, often a switched string of resistors so if the switch goes open, the current falls to the minimum setting, then feeding the second LM317 as the "normal" adjustable voltage regulator.
This gives a current protected variable voltage power supply.
 

joeyd999

Joined Jun 6, 2011
5,358
Long ago, I designed a high performance, low noise deuterium lamp driver for an HPLC (high pressure liquid chromatography) detector using an LM317 as a floating current source with 100V compliance.

It shaved about 25 components off the original design (using high voltage precision op amps) and performed better.
Hey! I actually found a photo of it on the internet:

Selection_035.png

This was designed circa 1995 or so. The flyback module in the middle produced 300VDC to strike the lamp, after which the LM317 (one of the TO-220s top right) regulated the anode current.

They're still selling these things 30 years later!
 

BobTPH

Joined Jun 5, 2013
9,138
I am just a hobbyist. I can only recall one use of LM317. I have a drill driver with a power supply that supplied, I think, 10.5V for charging. When it failed, I used an LM317 to regulate that odd voltage with a new transformer based supply I threw together from junk box parts. This was maybe 10 years ago and it is still going.
 
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