LM317 Voltage Regulator, help

hgmjr

Joined Jan 28, 2005
9,027
If you want to play it safe, send us pics before you power up and we can warn you if something looks askew.

hgmjr
 

Thread Starter

live4soccer7

Joined Jun 7, 2008
88
Here is a pic of the LM317 that I have soldered up. Sorry the pic is not the greatest, best I could get. The first pin I will have the input voltage. The third pin shown has two 33ohm resistors in a series and will give me a current of about 18.2mA and the second leg at the end is where I will connect a string (series) of 5 red LEDS. Let me know if anything needs to be adjusted. Thanks again guys!!

 

hgmjr

Joined Jan 28, 2005
9,027
The pic appears to show your resistance between Vin and Vout. If so that is not correct. The resistor should be between the ADJ and Vout.

hgmjr
 

hgmjr

Joined Jan 28, 2005
9,027
Vin should be pin 1, ADJ should be pin 2, and Vout should be pin 3. That's what it appears to be on the data sheet that sgtwookie supplied on the first page of this thread. Someone want to confirm this?
Remember, sgtwookie suggested the LM317L which is in a different package. You probably need to access the data sheet for the LM317T which will show the pinouts for the TO-220 package.

hgmjr
 

hgmjr

Joined Jan 28, 2005
9,027
Look on page 2 of this datasheet for the TO-220. You will notice that with the part oriented the way you have it in your picture, Vout is in the center and the ADJ pin is to the left of the middle pin.

hgmjr
 
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Thread Starter

live4soccer7

Joined Jun 7, 2008
88
After fixing it, I could not get a good picture, but here is what I have. From pin 2 (Vout) I have 2 resistors soldered in a series to equal 66ohm, The other end of the resistors are connected to pin 1 (adj pin), and the third pin has nothing soldered to it. That is the Vin pin. Let me know, I'm pretty sure that is right now. I will try and get a good pic and post it.

Yeah I took a look at the datasheet for the particular one I have and that is how I have it wired up right now. I am currently working on a really condensed 10 leds cluster. There will be two series of 5 in there and I will have a LM317 hooked up to each series. That will lights up a quarter of my dash. I will post some pics as I progress and can see some light. Assuming you guys wanna see something actually be accomplished. lol.
 

hgmjr

Joined Jan 28, 2005
9,027
The description you have given sounds like you have it right now. Still a picture is worth a 1K words.

hgmjr
 

Thread Starter

live4soccer7

Joined Jun 7, 2008
88
I will get a pic but it won't be to great. There is nothing connected to the third leg, it just looks like it maybe cause I had cut it short earlier. Hope you can make sense of this pic, my camera sucks and I can't get the manual zoom figured out and my phone is taking better pictures at the moment.

 
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Audioguru

Joined Dec 20, 2007
11,248
You can use an LM317 as a current regulator with a single resistor to set its current. The current is low enough so that the LM317 needs a minimum voltage of only 1.5V plus the 1.25V for the resistor.
Each series string of LEDs needs its own LM317 circuit.
 

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Thread Starter

live4soccer7

Joined Jun 7, 2008
88
Here is a pic of the LED Cluster that I was describing earlier. There are two series of 5 leds in the pic. So 10 3mm leds. I will get some more pics as I progress. Hopefully the ending result also.

 

Thread Starter

live4soccer7

Joined Jun 7, 2008
88
No, they are not lit, trust me, you know when these babies are lit. I just finished my first set of leds. I will post a pic when I have all four sets done and in the car. It's too hard to get a test pic of them when they are lit because I basically take it out to my bro's car battery and touch neg and pos sides to see if it works. lol. I have another pic here that I will have up in a couple of seconds.

This is one light cluster completely done: Three left to go, so there probably won't be more pics for a while unless somone has a request.

 

SgtWookie

Joined Jul 17, 2007
22,230
That's more like a "glob" of LED's! LOL! :)

Doesn't look like you have insulation on the leads of the LED. That may turn into a problem later, if someone bumps into the glob. You might consider using some clear silicone RTV at this point, since it looks like you've already soldered them to a PCB.

If you still have more boards to assemble, consider using something to insulate the leads. Clear shrink tubing works really well. For more rigidity, you could rip the ink pipe out of a Bic pen, rinse it out really well with isopropyl alcohol, and cut it to the lengths you need.

Red is a good color for avoiding night blindness. However, please make certain that you do not point any of the LED's directly towards the driver's head nor the front seat passenger's head. Super-bright LEDs can permanently damage vision, particularly if you look directly at them for a period of time - exactly what that time period is, I don't know, but I'm not willing to risk MY eyes! :eek:

I see you're using a pair of 33 Ohm resistors in series. That'll work - but so will two 120 Ohm resistors in parallel; and you'll get just the resistance that you need.

Resistance in series: Rtotal = R1+R2+...Rn
Resistance in parallel: Rtotal = 1 / (1 / R1 + 1 / R2 +... 1 / Rn )

As a FREE bonus for learning that formula... ;)
Capacitors in parallel are calculated like resistors in series: Ctotal = C1 + C2 +... Cn
Capacitors in series are calculated like resistors in parallel: Ctotal = 1 / (1 / C1 + 1 / C2 +... 1 / Cn)
 

SgtWookie

Joined Jul 17, 2007
22,230
You will take better photos if you are further from your subject by a foot or so.

Notice that in the photo you took with objects in the background a couple posts prior, the background objects are clear, where your subject is really blurry.

More natural light usually helps a lot. That causes the F-stop to increase (the iris closes down) which increases the focal length of the camera.
 

hgmjr

Joined Jan 28, 2005
9,027
Once you get things working you can look at ways to package the circuit with considerations for insulation and layout.

Sgtwookie's warning about the risk of damage to vision from the white LEDs is all too real. Heed his words regarding staring at the LEDs while illuminated.

hgmjr
 

Thread Starter

live4soccer7

Joined Jun 7, 2008
88
Those formulas sure do sound familiar. lol... Maybe from my engr 208 class. lol... I think I am going to leave them not insulated, the only way to insulate these would be to use a liquid insulator (that would harden obviously) and just cover them in it. They are methodically put together and the structure is pretty rigid and no one is going to be bumping into them because they will be behind the dash lighting up the gauges and what not. The There is nowhere where they will be able to blind me because the dash will dissipate the light color, so I won't get an direct beams in the eyes. I am going to insulate the back side well with electrical tape. Is there a liquid electrical tape type of stuff out there? If so what is it called?
 

Ron H

Joined Apr 14, 2005
7,063
As Bertus pointed out, the current source needs an additional 1.25V for the current set resistor, so your dropout voltage will be around 12V, possibly more.
 

Thread Starter

live4soccer7

Joined Jun 7, 2008
88
Each led takes 1.8 volts so 5*1.8=9v the lowest the supply voltage gets is about 11.3v so with the 1.25v that would be 10.05v left for the leds and stuff. So I am good to go on the circuit in regard to enough voltage. Thanks
 
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