The SimpleDrive2 - Very easy to set! Now with a feeler!

[rhd]

Re: LM317 - The SimpleDrive - Yes I was bored.

Is it adjustable via a pot?

If so, I'm still stuck on where to find a pot that can handle 1.5W ?

 

[Wolfman29]

Re: LM317 - The SimpleDrive - Yes I was bored.

It is adjustable via pot. You're right... my pot may not be strong enough -.- How do I calculate wattage? passing through a given gate? (Wasn't planning on making these for sale, but if I do plan that, then I want to get it right, damnit!)

 

[rhd]

Re: LM317 - The SimpleDrive - Yes I was bored.

Easiest way is 1.25 * your current. So in your case 1.25*1.25 = a bit over 1.5

I really think solder pads / bridges are the way to go

I wish I had you guys' knowledge and PCB generation abilities!

 

[jib77]

Re: LM317 - The SimpleDrive - Yes I was bored.

Here are some hints:
1) There is no way to get a pot that small rated for 2W. The big pots rated for 1W+ are expensive, which defeats the purpose of the driver. Use an array of resistors instead, make sure you use the proper package size for 1W and 2W resistors ... with those 1206 the max you will find is .5W and maybe .75W.
2) Those traces are way too small for the amount of current going through them. I would use at least 0.40" trace widths, use voltage and ground planes where possible.
3) Thermal pad not big enough. See datasheet's layout guidelines section.

Other than that it should work. :beer:

 

[Wolfman29]

Re: LM317 - The SimpleDrive - Yes I was bored.

Hmm, that's a problem then. What I may do is just use an array of two resistors in parallel and then just order a bunch of different resistors so I can preset currents... I am thinking maybe possibilities of:

2x 20Ohm
2x 10Ohm

etc.

Now I have to do some mods to my pad! Damnit!

 

[rhd]

Re: LM317 - The SimpleDrive - Yes I was bored.

I think 0.5, 1, and 2 Ohm would give you awesome (and useful) combinations

Jib: you know I'm just dying to see you do a version of yours with the 1085....

 

[jib77]

Re: LM317 - The SimpleDrive - Yes I was bored.

I think 0.5, 1, and 2 Ohm would give you awesome (and useful) combinations

Jib: you know I'm just dying to see you do a version of yours with the 1085....

Prototypes are on the way

 

[Johnyz]

Re: LM317 - The SimpleDrive - Yes I was bored.

A LM1117 in SOT223 package is made for only 800ma. Be careful not to threadjack...

rhd: If a reseller wants to buy, I get them fabbed on aluminum PCB and produce them.

 

[123splat]

Re: LM317 - The SimpleDrive - Yes I was bored.

I wish I had you guys' knowledge and PCB generation abilities!

Check out: CadSoft Online: Home of the EAGLE Layout Editor You can get the student edition free.

The fun part is making your own PCB's.. I use 'Press n Peel Blue' (a 'Xerox' toner transfer film) to transfer the Eagle Board circuit to plated bare board and etch with FeCl (the aluminum sulphate stuff is cleaner, but way more expensive).

 

[Wolfman29]

Re: The SimpleDrive2 - New budget driver.

Hmm. I checked the datasheet though and it said it could handle up to around 1.3A....

 

[Johnyz]

Re: The SimpleDrive2 - New budget driver.

I just checked "absolute maximum ratings" and yes indeed, but since the title of datasheet screams

LM1117/LM1117I 800mA Low-Dropout Linear Regulator

so probably at that current it's going to heat up like hell...

 

[Wolfman29]

Re: The SimpleDrive2 - New budget driver.

I plan on sinking it quite a bit =p My PCB is one sided, so the other side will be covered in aluminum =p

 

[Johnyz]

Re: The SimpleDrive2 - New budget driver.

I plan a small heat sink over my resistors, probably. Aluminum? We got enough of that INSIDE the PCB! :evil:

 

[rhd]

Re: The SimpleDrive2 - New budget driver.

If you're using appropriate wattage resistors, do they really need heatsinking?

I would be more inclined to heatsink the IC. If someone drives a RED or IR from two cells, your LM1117 is potentially dissipating 3-4 volts as heat. That's going to produce 2 to 3 times more heat than the current setting resistor (at least by my math, but I could be wrong)

 

[HIMNL9]

Re: The SimpleDrive2 - New budget driver.

Use a configuration like this one for the current setting resistors:

You cannot adjust the current from min to max value in a single step, but with this system, you can still made a driver that can be adjusted for a certain range (assuming you always keep the power in the pot tree at the maximum that the trimmer can manage, you need to calculate the values)

 

[Wolfman29]

Re: The SimpleDrive2 - New budget driver.

Well, as far as I know, there are no trimmers that are cheap and small enough to handle 1-2W and still fit inside of an Aixiz module... so I figure that if I do commercialize this (which I probably won't), then I would just ask for specifications on what current is desired or what range and I would set up the resistor with said current.