Building a driver.

[kiyoukan]

First sry its late ment to post in the help and tutorial section.
mod could you please move the thread,
again im sry just going brain dead.
Okay for the life of my i have tried to build two different drivers and cant get either to work.
I am in need of help i think more than words at this point.
I have all the right components and psu and such but for some reason every time i make it they don't work.
this is the first one
http://www.die4laser.com/dvd-rec/Die4Drive_files/Die4DriveRev1-2.pdf
This is the second one. (ttl last resort.)
http://c4r0.skrzynka.org/_hv/lasers/RGB_DRV.pdf
I wish i had the money to buy these pre built but i do not. However i have all the parts and tools even a now thing i found, CAIG CircuitWriter™ Pen - RadioShack.com
Use this on proto board to draw the circuit once i get it working on a bread board.
I have a nice webcam and fast internet connection. I am willing to pay what i can if any one would be able to help me sort this thing out!

 

[HIMNL9]

Sorry, what type of driver are you trying to build, exactly ?

A current driver for a pointer/handheld, a lab driver, a modulable driver for a scanner, analog or digital modulation ? .....

 

[kiyoukan]

A laser driver for my scanner.
With analog modulation.

 

[HIMNL9]

Something similar ? (old, but must not give you too much problems ..... if not, can design something different)

This is a basical application for a current regulator with a modulation input, usually works with resistive loads, but probably is ok also for a LD (anyway test it with a dummy load, i cannot test it myself now)

Power it with 12V, place at least 100uF 25V + 100nF on the power line, and be sure to not connect to anything pins 1 and 5 of the IC (they are NOT nc pins) ..... and don't use circuitpens for make a PCB, they are good only for emergency repairs on low current situations, not for make a stable work


EDIT: sorry, i just noticed i forgot to write a value ..... the resistor that go from the gate of the mosfet to the ground is 10Kohm

 

[kiyoukan]

I can understand most of that but there are some parts in that i cant read it.
This is also some of the parts i have.
I have a few other pnp a npn but i only have that n channel mosfet. I used it in both drivers so that could be my problem.
IRFZ20 N channel 50v 15amp 40w TO-220 Mosfet
2SC1815 2SC1815Y NPN 50V 150ma Toshiba
TL072 LOW NOISE J-FET DUAL OP-AMP
I also have a quad op-amp lm324
the only 1 ohm resistor i have is a 10watt but i do have a 10ohm 1 watt resistor.
Also some unsorted things from a pc psu.

 

[HIMNL9]

The irfz20 can be used with this schematic with no problems ..... the TL072 is a "double" op-amp (2 separate op amps in the same case, instead one), have a different pinout connection from the TL081, and is a low noise op-amp, so better (all the TL07x serie is the same of the TL08x ones, except for the low noise bonus ) ..... here is the datasheets for the TL07x serie, for the pinout ..... just connect the unused inputs of the second op-amp to the ground, if you don't want to use it as voltage follower for decouple the first one ..... the 1 ohm resistor is for sense the current, you can also use a 1,5 or 2,2 ohm, but better not go too high .....

Also, yes, better check if the mosfet is still good ..... or, for be sure, just get another one .....

 

[kiyoukan]

i have 10 of the mosfets so i have one that should work.
So can i use the 1ohm 10watt resistor? i could not find a 1ohm 1watt ar my local electronics store.
I am going to redraw the schematic to make things more clear for my self if you would not mind checking my redraw to make sure i got every thing right.

 

[Benm]

One warning about these circuits, also the first link in the opening post:

If you feed the opamp between positive voltage and ground, they MUST be rail-to-rail common mode opamps for this setup to work. So if you substitue the LM6654 opamp for a generic tl081 the circuit will probably not work, since it cannot read the voltage across the sense resistor.

 

[kiyoukan]

Okay so i put this together it does not show the lm7805 circuit but it will be in there to give the 5 volts out

I think that is every thing.
Please tell this looks good

 

[Benm]

Thats just wrong, and will blow up your laser diode.

The feedback to the - input of the opamp should come from the -top- of the 1 ohm sense resistor, not from the ground. The pencil drawing posted by Himnl9 has the same mistake.

Also, as i said before, a TL07x/TL08x opamp will not work when you feed it power from ground in this set up. It's common-mode input rage does not extend to near-ground so it will fail to work. Some opamps are able to work in such a setup, such as te ca3140 which has cmmir down to ground and slightly below.

 

[kiyoukan]

Okay thanks could you maybe draw one up like you were saying, it would be very help full.

 

[Benm]

I'm still prototyping here. The blanking signal that comes from the soundcard looks pretty weird as it is - so it'll definitely need a lot of work to sort out... its not nearly as powerful as the x and y signals.

 

[kiyoukan]

Would i be better off just getting a new omp amp?
If i got a rail to rail amp would this one work?
You are using a dac right?
I thought that modded the signal to make it stronger and keep it in range.

 

[Benm]

For this type of driver you'd probably need 2 rail to rail opamps to get it working with a singled ended supply voltage. I suppose the easiest way to do it is to first convert the dac singal to 0-5v, and then convert that to drive current for your laser diodes.

It could be done in a single step, but you would need precautions to ensure that the laser drive current cannot exceed the rated current. I'd have to inspect the souncard dac output closer to get any info on analog modulation though.

 

[kiyoukan]

Well i just want a simple analog or ttl laser driver.
I have documentation to build both the first one failed due to wrong op amps.
but the second one does not use them at all and i still had problems.
At this point for a small fee if some one can help me build either one if the first one i will just pray radio shack has the ones i need i dont want to wait another week or 3 for my normal suplier of parts.
It does not need to be perfect i just want it to work at this point.

 

[HIMNL9]

Thats just wrong, and will blow up your laser diode.

The feedback to the - input of the opamp should come from the -top- of the 1 ohm sense resistor, not from the ground. The pencil drawing posted by Himnl9 has the same mistake.

Also, as i said before, a TL07x/TL08x opamp will not work when you feed it power from ground in this set up. It's common-mode input rage does not extend to near-ground so it will fail to work. Some opamps are able to work in such a setup, such as te ca3140 which has cmmir down to ground and slightly below.

Hell, you're right ..... sorry, my error, i sketched it on-the-fly and paid not enough attention ..... apologize.

Also, the resistor from the op-amp to the gate is 47 ohm, not 10 Kohm ..... and no 390 ohm in serie to the 100nF capacitor, it's just in parallel with the 100uF one ..... and if you're using an LM7805 for the reference voltage, instead the 431, place another 47uF and 220nF also at its output, for prevent self-oscillations of the regulator ..... and the two little capacitors are 47pF (67 does not exist) ..... i know, i know, my calligraphy is simply impossible

Single power line ? ..... uhm, then yes, TL serie is not the better ..... probably is better to use LM158 or LM258 or LM1458, for this .....

I'm working at the moment and cannot redraw it better ..... when i have a pause i try to redraw it in a bit more clear way (sorry again, i'm from so much time in the electronic hobby, that always forgot that not all the peoples are used to draw and read schematics in my same way)