Leadlight Driverboard Schematics *Thanks to CHP*

[Enigmahack]

here it is:

Thanks again to CHP for providing this schematic - It looks good to me personally, however I also can't read schematics either lol

Take a look, see what you think and if corrections are required, send them to my e-mail address and I'll post it again /ubbthreads/images/graemlins/smile.gif

 

[Spec]

I dont remember there being any capacitors on the PCB...

On a side note, Im still trying to track down the manufacturer of and model number of the IC on the board. Will keep everyone updated.

 

[LaserMod]

I'm confused now /ubbthreads/images/graemlins/thinking.gif I have always thought these were capacitors (circled green).

 

[CHP]

Re: Leadlight Driverboard Schematics *Thanks to CH

Enigmahack,

Thanks for posting the schematic! I didn't know the values for the capacitors. My IC is made by ELM. I couldn't find the datasheet and the schematic is my guess at the pinout. I wasn't sure about the diode (or zener diode) too. Post the corrections and I'll update the schematic.

 

[Enigmahack]

Re: Leadlight Driverboard Schematics *Thanks to CH

Not a problem man - if you get anything else you need posted, send them to my g-mail accounts... Apparently my hotmail and ISP mail don't like your address :/

 

[Spec]

[ QUOTE ]
LaserModifier said:
I'm confused now /ubbthreads/images/graemlins/thinking.gif I have always thought these were capacitors (circled green).


[/ QUOTE ]

I apologise, they are, Last time I ran the fluke over the board I missed a contact point so I didnt "see" them as caps, just screwed up resistors (blew the driver board last time)

Lasermodifier:

Would you be so kind to publish images of the front and back of your driver board?

The one I have here is almost a 180 degree mirror image with the relay in a different spot.

Inconsistancy makes things difficult to trace.

 

[LaserMod]

Is this what you mean:

 

[Spec]

Exactly. There are small discrepancies with the locations of the devices on the board in my pictures. Interesting. I dont believe It effects the circuit by doing a quick glance, however it is interesting to note.

 

[LaserMod]

Yeah it is different...interesting I think that is the old layout I've come across it once before when someone sent me their laser to be repaired and that was 2003 manufacture date on the output label.

I still swapped the same resistors and the current mod worked fine to 550ma. Must just be the layout of components as to the schematic.

I can see scratches on them images Spec - is your camera still laserburnt? /ubbthreads/images/graemlins/eek.gif

 

[Spec]

Yes the CCD is still burnt, I have yet to decide if getting it repaired under warranty is justifyable given how I deestroyed it.

Besides, It gives me incentive to buy a new camera. /ubbthreads/images/graemlins/wink.gif

 

[sharkeeper]

Re: Leadlight Driverboard Schematics *Thanks to CH

Do remember that this applies considerably more current to the pump diode and it will die quickly if you do not use the pointer in moderation. You have been warned.

Cheers!

 

[CHP]

Re: Leadlight Driverboard Schematics *Thanks to CH

No corrections yet?

If the schematic is correct, then the reference diode (Dref) creates a reference voltage for the pot and two fixed resistors. The resistors "bound" the voltage the pot can see at its wiper which becomes the reference voltage. The circuit is a feedback current regulator. The current that flows through the LD goes through the 0.5 ohm resistor and develops a voltage across it (V=0.5 x Ild). This voltage gets fed through the lower op amp whose gain is 6 (1+ 10k/2k). So, the voltage at the output of the lower op amp is 3 x Ild. The feedback voltage gets compared to the refernce voltage (from the pot) and output of the upper op amp regulates the bias current into the transistor (Q) to make 3 x Ild = Vref (pin 3). This is the closed loop regulator action.

When you short the wiper to the + voltage (i.e., +3 volts or laser diode case) you are forcing the upper op amp to command the transistor (Q) fully on. The current through the LD depends on the current gain of the transistor (Q), the transistor's on-state voltage (Vce), the LD on-state voltage, the voltage drop across the 0.5 ohm resistor, the supply voltage (battery voltage), and the battery internal impedance, etc. When you do this mod the current through the LD is no longer regulated and will vary based on the battery voltage.

One way to run at higher currents and not see a current drop off, you have to increase battery voltage and perhaps change the 2k resistor in the lower op amp circuit to ~4k. (There are other ways too.) This will reduce the gain from 6 to 3.5 which will let you regulate higher LD current. I don't know about the power ratings of the components in this case.

 

[sbk]

Re: Leadlight Driverboard Schematics *Thanks to CH

I think Dref is a Zener diode and acts as a voltage regulator.
The regulation is effective only when Vbattery > Vz (also Iz current <> 0). For my laser the board regulates with min battery voltage = 2.4V.
The resistor in serie with the Zener is a current limitator.
Otherwise the rest of your analyse seems to be ok...