Regulated psu and microboost trouble

[chipdouglas]

Hey guys, I finally manned up and bought a regulated dc power supply. It's a 30v and 5 amp max rated. I've toyed with it with some LEDs and 1 laser diode and it works pretty good..... Buuuuuut when I hook it to my microboost that is soldered to my ld, my ps will just keep ramping up the current to my ld. Know the ld is getting all the current because it clearly and visibly keeps getting brighter all the way up to 2.2A. I haven't pushed it further. :wtf:

I'm pretty sure my mb is set to 600ma. It could be broken but idk? I left my multi meter at work so I can't test it. But I do I have a new flex that I purchased preset to 1200ma so ill try that too.

I don't have a question per say, I just thought I'd put this out there. I'll post back later with my findings of my flex.

Edit... Ok, I put my new never used flex drive on. Soldered ld to board. Hooked up my regulated psu and same results. The seems all current goes to ld. Although the flex drive flashes when it starts to overheat. But when I power driver/ld via battery it works great.

So now I have a question. Am I doing something wrong, or is this a well known thing?

Michael

 

[Cyparagon]

Bench power supplies often have problems powering switching devices. This is because the switching frequency is often faster than the power supply's response time. That usually results in the power supply hitting the current limit though; you're experiencing the opposite.

Sounds to me like maybe you're trying to power a current source with a current source. When powering the driver, the power supply should be in constant voltage mode (have the current limit set to max), and the voltage set to an appropriate value for the driver. 3.7V in this case.

 

[chipdouglas]

My power supply wont really let me adjust any values visually.
In my limited experience i need draw on the psu to be able to set it.
Example. When turned on under no load i can turn all knobs all the way to max
And see nothing on psu lcd. Now when i power straight laser diode with out driver, if all knobs are turned to min, and i ramp up current nothing happens. I.need to turn voltage all the way up and ramp up current slowly, the voltage will adjust accordingly to ld max. I assume you want me to do this but with voltage instead of current.??? Ill try later, im in boston for work.

 

[ped]

Cyp is right.

These drivers have real problems with bench PSU's. Its like trying to drive a driver, with a driver.

I always use two paralleled 18650's to set up drivers, if the bench psu is in CV mode ( current limit set to off) and its not working, it simply ain't going to. If you adjust current or voltage while the driver is under load, its going to try and compensate.

 

[Cyparagon]

I assume you want me to do this but with voltage instead of current.??? Ill try later, im in boston for work.

Yes, your method is how you drive laser diodes or LEDs; it's not for drivers. You will almost certainly damage your driver doing that. This is because the power supply ramps up voltage (up to 30V in your case) trying to push more current through the driver. I'm guessing the flexdrive doesn't operate well at 30V.

Drivers want constant voltage ideally.

if the bench psu is in CV mode ( current limit set to off) and its not working, it simply ain't going to.

Well, adding a large filter cap between supply and driver will usually solve the problem. This will smooth out the current draw pulses. Use an electrolytic - the biggest value you can find. For added safety, you might want to select one with a voltage rating greater than the max voltage of your power supply. As you might know, they will have a shit-fit if over-volted. You'll be cleaning up foil, paper, and metal shrapnel on the other side of the room and possibly from your face.

Note: do not use a filter cap when operating in current mode as it can destabilize the supply.

 

[chipdouglas]

Thanks for the help guys...

Cyp, are you still interested in doing those led drivers for me? If not, no worries.

 

[Cyparagon]

Yes, I can still help you with those.

 

[Flaminpyro]

This is why I use a 18650 cell to set all my switching drivers, even my $400.00 Agilent U8002A power supply gives the same results :cryyy: