808nm "lethal" supply

@dzrick
Just a second. Where are you located at? (asking because I saw the attachments names...)

Well here it is updated, I'm messing around with the TTL part trying to figure out a few things first. Anyway, the circuit seems pretty stable I tried to create a zener diode voltage reference but that seemed to eat up my current once I started the circuit, I didn't want to move R4 so I decided not to use the zener, insted, to ensure that there are no fluctuations to the op-amp, I've increased C2 capacitance to allow current to get "ramped" to 20 Amps in ~15 seconds...

Well.. I've ordered some parts my plans are not to roast them.. let's see what happens..!

Once again thanks, I hope this does what is supposed to be do.

:drool:

Leodahsan I'm @ Portugal..! Lisboa..! =)

Alright, it's beginning to look like the correct circuit. There are still a few modifications needed though
to get it to work properly in the real world.

First, the voltage source connected to the gate is bypassing the regulation of the op amp and turning
the FET on hard. That will blow everything up - FET, diode, everything. Remove it completely.
Then all you need is a single 10Ω resistor between the FET's gate and the op amp. No ground
connection here, either

Also, keep in mind that R4 is going to be a current sense shunt and not a regular resistor at these
levels. I know I've said this before, but it will be pretty obvious anyway since there aren't many (probably
not any) 0.03Ω resistors out there, especially non-inductive ones.

C2 should be removed. It is going to prevent the op amp from going low when the TTL is switched.

Remove C1 from ground and instead connect it directly across the diode. Other than that, the circuit
exactly as drawn will give you a very good headstart.

Don't forget to also get a bunch of 100A diodes to use as a dummy load. Get it scoped and working
flawlessly before ever connecting the laser diode.

For the current shunt, I recommend using a couple of Vishay SR5s in parallel. They each handle up to 5W and are not very inductive since its just a metal strip. I use them quite a bit.

http://www.vishay.com/docs/31067/sr.pdf

Its good you've got the feedback loop in there, and some protection in mind.

I also think its a great idea to "scope" the circuit on test diodes, looking at the startup and shutdown transients especially.

The Lightning Stalker said:

First, the voltage source connected to the gate is bypassing the regulation of the op amp and turning
the FET on hard. That will blow everything up - FET, diode, everything. Remove it completely.
Then all you need is a single 10Ω resistor between the FET's gate and the op amp. No ground
connection here, either

Click to expand...

Actually, do you mind elaborating on this? To me, it makes sense to stick in a 1M pull down resistor on the gate.

Is the op amp guaranteed to be at 0V at start up? Is it possible to know that node won't float prior and during start up?

The Lightning Stalker said:

First, the voltage source connected to the gate...

Click to expand...

That's a voltmeter. ... I think.

The Lightning Stalker said:

all you need is a single 10Ω resistor between the FET's gate and the op amp. No ground
connection here, either

Click to expand...

I think it's risky to leave gates with no pull-down. The gate will stay charged when the circuit is powered off, and then potentially pop something when it is powered on again.

Hello there!

It's nice to see so many constructive critics, well, I don't have much time since I've got a new job (hurray!).

I will first start by saying that my baby is already waiting for me in the Post Office... my friend needed my signature so I couldn't pick it up today, anyway, also my new reprap J-head has also arrived... time to get creative on various "front lines"!

Well, starting from the top down here it goes, all the green numbers are meters, I've used some to have a "hint" of what was going on over there, the op-amp, depending on POT resistance can get 0V on + rail, what I think is weird is the meter on the Vg on the FET stays @ 4.09 thus keeping the FET allways open... this could be bad if (in real life) there is actually some voltage building up there, but even if I disconnect the load the voltmeter still gives me insane voltages... like +134 volts or more!! :O

Well, if the OpAmp only outputs a bit above the + rail... this doesn't make any sense... I guess it's a software bug anyway, here's what I mean (on pic_1):

Well, about the capacitor C2, I have placed it across the Laser diode but the results weren't very good, the thing would burst in amperage (to whatever I would set the POT) and on the Oscilloscope (on the laser output) the ripple had came back, so I've decided to stick with the values on C2, It seemed to me that changing this value will attenuate the rippling according to amperage that is being drawn by the load, or, I could TTL after the laser itself, since the circuit is already limited I would (i think.. correct if wrong) be able to shut it down "right from the source"... but I think it would interfere on how the Op would read the current and probably "drive the FET crazy".... hum not a good idea!

Anyway, C1 also remains the same because that can actually prevent some crazy spikes from coming into Vdrain and... I have some big capacitors laying around that I don't mind "testing"... But nevertheless I still putted it across the Laser diode (aka Output)... After reading your advice this seemed keen to do.

Meatball, that was actually the kind of current shunt I was looking for!! And it has the sense current needed to drive this circuit, I was going to parallel 1% resistors on a big board to make the sense resistor that might have saved me a bit

Like Cyparagon said, I need to keep that ground on the FET, once the power goes down, like he said, I need the remaining current to be driven through that bleed resistor...

I will use some 100A diodes to test the thing out first, don't worry.. let's see what happens. Anyway I'm going to take a better look at this circuit and as soon as I can, I will post something.

Check out Pic 1 to see that weird bug.. actually that's what is bugging me most...

Regards to all!

If this is not the "final" it is almost there... a tweak here, a tweak there...

I suggest you consider using a few mosfets in parallel with source resistors to force current sharing. One TO-220 device is good for 50W of dissipation no matter how much current the device can handle.

5V-2V*30A is 90W. You'd need atleast two if you have an infinitely sized heatsink, if it were me I'd use no less than 4 and add fan cooling.

Okay, I stand corrected. Cy is right about the pulldown, etc. and 330Ω is probably plenty since this is linear and not switching. There are still some changes involving C1 - C3.

Hello guys!

I know I've been away for a while but, now that I've got a new job things became a little harder to do, also there is another thing that is taking my time.

Finally my 3D printer project is "almost" over, I can print parts and I've been dedicating my time to it, I know it's a totally off topic but I want to share what i've been up to..!

I've built this machine to build another one that uses a laser and UV curable resin or to cut some plastics and wood for a start but once it becomes possible I'll need to get some decent optics to make a spot out of a bar..... (I didn't think about this yet... but I've heard and read that is a pain in the a**)!!

Here are some pictures of my "Cable Mountain machine"..!






It's not perfect.. but it is making usable parts, wich is my objective for the beggining..!

Anyway, since this project is almost done I'm going to resume the drawing of the laser driver, that is indeed an enjoyable headache..!

Lightning Stalker, that's exactly what I'm looking for in order to drive the laser via TTL, I will update my circuit and post it here as soon as I can!

Sorry for the "OFF" topic, but somehow I wanted to show you guys my objectives, what I'm doing and... hell have fun!

Regards to all!

Ok, after a while struggling with my "prusita" (prusa + mourita) :wave: yay!
on wich I did some improvisations with some alluminium profiles I've had here for a while (that I've used for the former co2 laser cutter), I've finally bought the parts needed for this project.

Well.. some resistors are missing (yet) but after NYE I'll go get the rest.

Parts list:

1k0 .. 2
2k0 (???) .. 1 (this one I can't identify my room light is yellow and the bands are too small!!)
10k .. 1
15k0 .. 1
330r .. 1
0r33 5w +-5% (coiled) .. 16 (missing 4)
1k pot .. 1
100r .. 2
IRFP150 .. 2
LM324 .. 1 (x2 including spare... just in case..!)
25v 4700u .. 1
50v 220u .. 1
50v 1u ..1

Why so many resistors:

Simple, since I couldn't find a 0.03 ohm resistor I'll put them in parallel along with 2 IRFP150, I'm thinking of using protection diodes across the FET's, I don't think how necessary it'll be since I've got the big cap that is supposed to absorb most of the spikes anyway, the circuit board is not yet designed (hoping I'll do it today or tomorrow before NYE) so I can put the hands on the job again..!

I want to see my baby flash but without the 'strobing' if you know what I mean...

Well this was mainly to keep you guys posted!! Didn't come here for a while!

Regards to all and happy NYE!!
Don't drink..........(water) ( for those who are older! you kids gotta wait )

The Lightning Stalker said:

OAR5R003JLF

Click to expand...

Well thanks for the tip!

Anyway, even if this isn't the right resistor value you just pointed me the right place to look for! I tought they were more expensive but it seems not..! Anyway, before I buy those, I'll use what I have. Only yesterday I've realized that I only need 10, about 5 per transistor (since I'm using 2), wich will drag about 22 amps each..!

MORE than enough! Once again, thanks!

Hello everyone!

Well, I know, this post is oooolddddd, but I decided to make a huge return, first of all, I am really sorry for the delay (well... It's been a few years! > hey in he beggining I told it could take 4 to 5 years! Kinda nailed it!) but I just wanted to tell you that this project was never forgotten and I hopefully will be able to finally put an end to it!

Reasons I got "away" for so long:

• My new job took my life (still working on the same company thou, but it really consumes me a lot of time)
• And I now have a child that is almost 2 years old so... as you can imagine "man caving" kind of ended. Until now

Eventually I got a new laser cutter (wood only) one of those cheap chinese ones, still woks, and 2 other 3D printers... Made myself a nice electric foundry to be able to make nice metal thingies (heatsinks for lasers for example), just to sum up what I have been up to!

I decided to ressurect this post because I will finally build this DC-DC converter (if I ever get to find the files ahah [or I'll just follow these drawings]), I do have all the components thou... What I'm not sure is about the (60W) laser diode, it's been sitting for a while waiting to be lit, and if I stand correct it could have some issues, anyway, the diode is secured in a dark dry place !

If I end up being able to TTL the device and if I end up making a decent PSU for the laser I'll try and aquire teh colimating lenses (FA / SA) lenses along with an f-theta lens as I already have the Galvos too (30.000 kpps) .

Let's hope for the best, and again sorry for the late "come back" !

I'm bumping this because there are still some members active here that posted on this over 6 years ago that might of missed this comeback