any difference between a "Laser diode driver" and a regular "step-down/buck"?

[Mannitu78]

hello,
ive just been searching for drivers on aliexpress and realized. whenever a circuitboard is sold as Laser diode driver, its much more expensive than a regular buckconverter or stepdown-power supply. If it doesnt include laser driver in the title, its much cheaper. So im asking myself if i am missing something, is there any difference?

there are lots of bucks that are dirtcheap, like 1 or 2 dollars. they have adjustable output current and voltage and its all in the range of what a diode would need. Gonna link 2 of them. So would they make a functional driver or is there any component missing?
is it about output ripple in v? Can that be a problem?

0.82US $ |3A Spannung regler lm2596 LM2596S DC DC 3 40V einstellbar step down power Supply module|Spannungsregler/Stabilisatoren| - AliExpress

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1.7US $ |DC DC Buck Step Down Modul LM2596 DC/DC 4.0 ~ 40V zu 1,25 37V Einstellbare Spannung regler Mit LED Voltmeter|Spannungsregler/Stabilisatoren| - AliExpress

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1.65US $ |5A DC zu DC CC CV Lithium Batterie Schritt unten Lade Board Led Power Converter Lithium Ladegerät Step Down Modul XL4015|Spannungsregler/Stabilisatoren| - AliExpress

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[paul1598419]

Laser drivers are current regulators. Most buck converters are voltage regulators. Some come with a maximum current output, but that doesn't do the job you need done. Unless you are good at redesigning the buck regulator you will be much better off buying the driver you need.

 

[Mannitu78]

ah i understand..only voltage regulation..but if the bucksdoes have exactly the current output you need for a certain diode, it would work?
Also what about LED drivers? they are cheap and have current regulation?

 

[paul1598419]

Buck voltage regulators can never be used as drivers for laser diodes. Some have had success using LED drivers, but those are typically more noisy and that can cause laser diode failure. Good luck.

 

[Mannitu78]

could you clarify why buck voltage regs can never be used? Lets say it has 2A output and i have a diode that runs on that current? Whats the difference in circuitry-terms? I mean between a buck and a laserdiode driver?

And is a LED driver build differently than a Laserdriver?

i mean, by what is a powersource defined, its by output voltage and by output current right? And theres also voltage and current ripple. Is there any rule how much ripple of v/a a diode can take?

 

[paul1598419]

A laser diode needs a current regulator because the diode tends to decrease its resistance as it heats up and a voltage regulator will only stay at that voltage that it's been set to. That means as the diode's resistance decreases the voltage regulator will allow the current to increase. When that happens the diode will go into current runaway and will fail.

 

[Mannitu78]

interesting..i think i will still put it on a buck, just to see that effect. And on a laserdiode driver, the current doesnt change when the diodes resistance drops?

i wonder because i saw a guy build a driver for a 1watt diode simply from a cheap voltage regulator for a few cents and a resistor, i think it was. Didnt say anything about how long this will work though.

 

[paul1598419]

In a cheap laser pointer you can use only a resistor as long as the current allowed to flow is below the voltage of the batteries and it can never get to the point where even if the diode had 0 ohms resistance the current is limited to just E=IR.

However, if you use a buck voltage regulator and the current is not limited in the way I have said as the diode heats up its resistance drops and that will make the current increase until the diode gets so hot it goes into thermal runaway. The diode will then fail.

 

[Mannitu78]

ok and could you please clarify for me the difference between LED and Laserdiode drivers? The driver from my 1,6w China-Laser also had LED + and minus printed on the board. It has current regulation. So why are Laser diode driver more expensive than LED drivers?


also what about that thing from above...this seems to have current+voltage output regulation?

1.65US $ |5A DC zu DC CC CV Lithium Batterie Schritt unten Lade Board Led Power Converter Lithium Ladegerät Step Down Modul XL4015|Spannungsregler/Stabilisatoren| - AliExpress

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[paul1598419]

Most LED drivers are quite simple in their design. Not all laser diode drivers are very expensive. It depends on where you get them. Lazeerer was a member here who used to build and supply drivers that were the best we had, I used to buy mine in bulk from him. Astralist also used to make and supply drivers too. These people are no longer around. The driver you have listed is actually a voltage regulator. It also has a current limiting control, but you cannot have both current regulation and voltage regulation on the same buck regulator. Current regulators allow the voltage to fluctuate as they hold the current constant. Voltage regulators do the exact opposite.

 

[Mannitu78]

yeah i think i understand, i just wateched a few things about constant current sources. I think ill be soon able to buiuld my own one. Doesnt seem that complicated after all.

 

[paul1598419]

Good. I'm glad you are getting it. I have built many lasers and that is actually quite fun to do. Good luck to you.

 

[Mannitu78]

what do you think about this driver? I bought this 2 years ago and just hooked it up for the first time. It seems to be decent quality, at least it looks to me. Its pretty popular on Ali and goes for about 10 bucks. It also has a 12V Power supply in, in think its used for laser engraving machines.

However, you said a driver cant have current AND voltage control. I def. do not know how do make one XD..but this driver has 2 regulations, the small one is the usual potentiometer, it regulates current, i already tested it on that pocketlight-LED. But theres a second potentiometer, the blue one. Turning it does not affect current, so i guess it has to be voltage? I also dont understand. Because if you put in a certain resistance, if the current must stay fixed, than the voltage must change, right? Ill try to measure voltage, not sure where to put the probes yet.

edit: well, i also measured voltage, the Voltage drop through the LED diode, it didnt change when i turned the blue poti. I guess this poti has to do with the "Fan" or "TTL" terminal...dont even know what the TTL is supposed to do.

 

[paul1598419]

Even current regulators do so by varying the voltage out. Engraving lasers do so by varying the voltage very quickly, but the current is still limited to a maximum current out. That driver is likely a reasonably good one for this purpose, though I am not specifically familiar with it.