Can someone help me with my circuit schematic?

[Ecibob]

I am having a bit of trouble getting my circuit to work. The PCB has been built and the circuit is being testing.

We have a 12v power supply input. There are two seperate diode connections here for 445nm high watt (~2W) lasers. They are both supposed to be controlled via TTL, microcontroller.

now the pot adjusts +/- .20v. However, the voltage is still not adjusting with the TTL input. It's still staying around a constant 4.7 - 4.9v (depending on pot). I connected the ammeter and it shows 4.8v/.4A

I'd glad to give any more information if you need, but can anyone spot a problem with the circuit? I've been trying for a while to figure it out.

 

[Cyparagon]

I don't see how R13 and R14 do anything productive. 10k in parallel with 560mΩ has no effect, except at the WAY bottom end of the turn, where you short out your current limiting resistor and blow the ass out of the laser.

D2 and D3 are not needed with D1 in place.

2A rating on D1 is insufficient for two diodes, since two diodes will take up to 4A.

T1 and T2 have incorrect notation. T is for transformer. You want Q.

R9 and R10 are not needed, as the caps will discharge via the divider networks (R5/R6 and R7/R8 respectively)

How are you heat sinking the LT1083s?

What is the current rating of your 12V supply?

What are the voltages on the base and collector of T1 with TTL low?

What are the voltages on the base and collector of T1 with TTL high?

Where are you checking current with your ammeter?

Be aware that your large caps (C3/C4) on the output will slow the TTL response.

Why are you using constant voltage instead of constant current?

 

[Ecibob]

Thanks for the sincere reply Cyparagon!

I'm going to try your suggestions. Taking out R13 and R14, the two 10k pots. Taking out R9 and R10. And removing the D2 and D3.

So basically removing half of the driver circuit after the LT1085

We have a large heat sink on the regs.

As of now, to answer your questions: the voltage is not changing with the TTL input. The current at the test points is .4a at 4.8v. I guess when you mean 'using' constant current, you are referring to the power supply setting? I was under the impression that the circuit drives the diode with constant current. (and that is what cutting diodes need anyways)

I've attached the PCB and what I'm going to do with the schematic. Maybe you can spot something I missed. Thanks again.

Sorry for the huge pictures!

 

[Cyparagon]

Those were side-points. They won't fix your main problem.

The current at the test points is .4a at 4.8v.

Which test points? You mean at LD1? Do you have a load when you're checking this, or are you putting the meter into ammeter mode and probing the pins directly? Because that's a bad idea for your constant voltage setup.

I was under the impression that the circuit drives the diode with constant current.

Not what you've put together, no. You've programmed the regulator to output 5V, and TTL high should bring that down to 1.25V. That 5V is limited with the large resistor, but the current will still vary (increase) as the diode heats up. That is because the forward voltage on a diode decreases when the temperature increases. Therefore, the voltage drop (5V - Vf) on that current limiting resistor will increase, and ohms law says that is a current increase.

Compare the standard lm317 constant current design with what you've designed:

What you've got will probably work, but it's not constant current. Remaining unanswered questions:

What is the current rating of your 12V supply?

What are the voltages on the base and collector of T1 with TTL low?

What are the voltages on the base and collector of T1 with TTL high?