Step down circuit for laser control, help me to improve it.

[dunkelheit_phoenix_2008]

Hello there, I would really appreciate any advice, constructive idea or anything that could be improve on this circuit, it's design for a 4.5A laser diode. Thanks for your help.

 

[FireMyLaser]

I dunno man, why are you using so many different parts? Also Q6... Whyyy.

 

[WizardG]

And that "feedback signal" looks like voltage to the diode, not current through the diode.

 

[Encap]

And that "feedback signal" looks like voltage to the diode, not current through the diode.

It is a continuation of the OP back and forth presented here - https://laserpointerforums.com/thre...-design-for-5v-5a-laser-control.107733/page-3 see posts #34 and prior for background.

Cyparagpn in post #35 advised:

You've been told half a dozen times now you need current feedback, and you continue to ignore this.

 

[Giannis_TDM]

Hello there, I would really appreciate any advice, constructive idea or anything that could be improve on this circuit, it's design for a 4.5A laser diode. Thanks for your help.
View attachment 71863

So it didn't work after all... seems like me and cyp were right.

 

[Cyparagon]

Hello there, I would really appreciate any advice

Don't fucking lie to us. You've ignored all advice you were given, time and time again. Just leave.

 

[Unown (WILD)]

Yeah I don't get it. If you want it to work why not listen to what they told you? At least give it a try or something I dunno

 

[dunkelheit_phoenix_2008]

And that "feedback signal" looks like voltage to the diode, not current through the diode

Got it, I'll implement a loop for current feedback as a trigger.

 

[dunkelheit_phoenix_2008]

Using R15 as R_Shunt I can feed the system, but I have a problem, I've heard that soft startes can reduce the peak of the step down on the first microseconds, I know that C4 produces that voltage peak (right now I'm on less than 2% of ripple voltage), mi point is, due the thermal resistance of the laser, I must ensure with R15 the current limiter, but I can't upgrade the resolution of the system due C4, snubber ciruits doesn't solve the problem; can you all, please, present me a solution or an alternative to have a quick starter with a high mV resolution, and without that bothersome voltage peak? Thanks!

I'm using it as a second protection against flyback current, in addition with the reverse internal zener diode of the laser, IRF1404 internal diode allows me to handle that problems, with 60% of efficiency, at leat 121.2 A. Do you consider that this protection is too much? Thanks for add good comments.

Edit: Corrections done, there are my proofs.

 

[FireMyLaser]

You already use 4 different diodes... Don't you think you can reuse any of them, instead of using the parasitic diode of a mosfet as a fifth one?

Is this maybe a joke you make? Was this your inspiration?

 

[ArcticDude]

I'm using it as a second protection against flyback current, in addition with the reverse internal zener diode of the laser, IRF1404 internal diode allows me to handle that problems, with 60% of efficiency, at leat 121.2 A. Do you consider that this protection is too much? Thanks for add good comments.

Stop double posting!

 

[Encap]

Double posting back to back is very frowned upon and annoying.
Triple and quadruple posting even worse.

Use the edit feature to combine everything into one post instead of making multiple posts.

 

[dunkelheit_phoenix_2008]

You already use 4 different diodes... Don't you think you can reuse any of them, instead of using the parasitic diode of a mosfet as a fifth one?

Is this maybe a joke you make? Was this your inspiration?

View attachment 71891

Are you saying that I should use another Schotty diode instead Q6? I'll have only one reverse protection (the internal zener of the LD) removing Q6, that's the problem, my inspiration is that I want the system as secure as possible, kind of Alkatraz.

 

[FireMyLaser]

I want the system as secure as possible

Then you should use a linear regulator. If your controller glitches/crashes due to outside EMI or whatever else, then the laser can be fed 12V dc. It will be inefficient, but also reliable.

 

[dunkelheit_phoenix_2008]

Then you should use a linear regulator. If your controller glitches/crashes due to outside EMI or whatever else, then the laser can be fed 12V dc. It will be inefficient, but also reliable.

I've already implemented an EMI/RFI filter in the power supply (the X1 X2 ones), I'm using an exclusive source for the laser, but same ground due communications. Some experiments with LM317 using TIP41C transistors, and LM338 experiments, shown me that linear systems are not good for the laser control. Other point is my dutty cycle is limited at 45% due inverse amplification Q2. You didn't answered my question.

 

[FireMyLaser]

yes