opinion on this LM2596 based driver

[cyclonite]

Hi all,

I can't ignore the fact that this driver costs just £2.99 and is both constant current and constant voltage adjustable. It seems to be of quite good quality.

Question is, what's the catch here?? With my limited knowledge I'm not sure what else to look out for and could use any opinion.

I've received this in the post today, I must say the PCB's surface is cheapish looking and even the underside has someone's fingerprint oxidised onto the copper surface. But for this price I could use this to drive a 2A 445nm diode right?

Thanks.

LM2596 DC 7V-35V to DC 1.25V-30V StepDown Adjustable Power Supply Module LED td | eBay

 

[sinner]

From my experience you would be better off with the mainstream drivers like blitzbuck - x-drive - fmt boost to mention a few..
Secondly this driver is a huge ass pcb for a handheld built but it wont hurt to incorporate one of these into a labby..
These are designed for 3A-4A applications of higher power LED's i suppose, so you might have an overkill for a driver..
Just my 0.02

 

[cyclonite]

Ok thanks.

The item's description on one of the listing was it's suitable for anything under 2A. This seems to be different on this one. Maybe it's a different batch.

I'll hook it up to the Ampmeter one of these days to see what the max A it outputs. Might have time to do this tomorrow.

Yes I agree about the PCB's size, I think I'll have to house this in a plastic project enclosure hehehehhe.

Cheers

 

[Cyparagon]

Looks like it'll work. I'll get this one and do a review.

 

[Bionic-Badger]

You can always just grab one and then test it out on a higher powered LED like a Cree. That's what I do with experimental drivers so I don't bust something expensive.

 

[cyclonite]

How is that different to the one that I have apart from the middle pot which allows you to set the led colour change? You only need that for charging batteries.

I don't think it comes with that large black heatsink in the middle picture or does it?

Looks like it'll work. I'll get this one and do a review.

 

[sinner]

You have two adjustable pots in the first version, You can use it as a Lithium Batteries charger by adjusting the Voltage..
Second pot would be adjusted while attached to a Testload and current can be adjusted to below 2A aswell, It is definitely a useful driver OR more of a ANALOG BENCH PSU imo!

 

[cyclonite]

Hi guys,

I have a problem with this driver. So here's what happened:

1) I hooked the driver directly to ampmeter (short circuit) as per the instruction and cranked it up till I get a reading of 1.2A

2) I set the voltage to what I want, 1.9V

3) I hooked it up to a series of 1N4001 diodes (dummy load). I find that the more diodes I add, the less current goes through the output circuit. What's the point of having a constant current + voltage driver if that was the case??? By the time I add 3 diodes to the circuit, the current dropped to 200mA

Now the worst part is, I can't seem to crank the current up to 1.2A even by turning both pots. I tried adding a 3rd battery to the input to no avail. I'm using 3 x RCR123A.

So what should I try next?? Thank guys...

 

[DTR]

Are you keeping the input voltage above the voltage of the load plus the dropout voltage of the driver? Sounds like it may be out of regulation. What voltage are you applying from your power source?

Edit:
Also you said you had set the voltage pot to 1.9V so if you go over that forward voltage by adding more diodes to your test load it will also drop current. If you are going to use it with a 445 I would set it to around 4.8V and then the current to zero and adjust up the current once you have it on your test load with the proper amount of diodes to simulate the 445 diode.

 

[Bionic-Badger]

Those power supplies--like all things--are subject to Ohm's Law, so they can only work in either constant voltage (CV) or constant current (CC) mode. If you set current, the voltage must vary; if you set voltage, the current must vary. You can't have both unless you're somehow also able to change your resistance (again Ohm's Law).

The way to use those drivers in CC mode is that you set the voltage for the driver to the very maximum (i.e. no voltage limit). This ensures that the voltage can vary as necessary with the current. Then use a multimeter or dummy load (better option) to set the current.

If you happen to set the maximum voltage too low, what might happen is that the driver "encounters" that limit first, and therefore the current will change as a result of Ohm's Law. This video kind of explains it (with light piano music in the background):

 

[DTR]

I would like to get an opinion on this.

The reason I suggested 4.8V is that on my bench power supply I have noticed if I set the voltage to say 12V and the current to zero it on occasion will spike and kill the diode but when I set the power supply to around the max forward voltage of the diode and the current to zero I have never lost one.

So I usually suggest with a power supply or a driver like this not to turn the voltage all the way up but put it toward the upper threshold of the load. Is this not a good piece of advice especially since it seems no one that has chimed in has used this driver to power a LD that can tell us how clean it is?

 

[Bionic-Badger]

It could be helpful to set the voltage to the expected Vf of the diode, perhaps to protect it from the surges you describe (assuming it has that effect for the driver). I don't know if setting a voltage limit is a mechanism that will prevent such surges, but it probably can't hurt.

 

[cyclonite]

Thank you both so much. I think it may be hitting 2 limits here. Firstly it's hitting the forward voltage limit which explains why the LED turns from green to orange when I use 1 or 2 diodes in series as my load but as soon as I add a third diode it stays green and the mA output becomes very low.

The second could be that my power source of 2 RCR123 may be insufficient and this could explain why at some setting I get the same mA reading with 1 or 2 diodes hooked up but it falls down with more.

Tonight I'll hook this up to my 12V SLA battery (meant for UPS) and try this again. That way we can be certain the input is sufficient. The driver can take a max of 15V input so this should be OK.

DTR, thanks. This is for my 1W 808nm project which requires 2.2V at 1.1A. When I hook te actual diode up it only put 200mA through it so it could be one of the reasons above. I thought maybe the diode was dead but if it can't power the dummy load then that's probably a premature judgement.

 

[cyclonite]

Hi guys,

I've quickly tested some new settings and have observed the following:

1) You guys are right about the driver cutting the mA output once the voltage drop exceeds a certain voltage drop, however..... see point 2.

2) I had to crank the voltage output up to 3+ volts to get it to drive 3 x 1N4001 diodes in series. From my calculation this dummy load should only have a drop of 2.1v across (average 0.7v each). Hence I don't understand the need to crank it up that high.

3) 2 x CR123A are enough to power the driver to put out 1.1A at 2.1V

4) I hooked this up to a free 100mW IR diode that is meant to be driven at 2.2V at 1.2A. The diode lit and I could see a purple glow with my camera, however I'm not sure if it's at the correct brightness for 100mW. How can one tell without a sensor?

OK, when I shut everything off and tried to remove the diode from my alligator clips it burned my finger. Ouch the diode got so hot from just a few seconds of usage.

Question:

1) How can I tell if this diode is died (became an LED)? With the other wavelengths it's easy to tell from its brightness but IR is invisible. So my question is, if the diode is become an LED, would it still draw the same current i.e. 1.1A?? or would the voltage drop change, etc?? can we tell this electrically rather than optically?

Thanks.

PS: Tonight I'll measure the actual voltage drop across the Laser Diode with everything hooked up as it is. I forgot to do this earlier.

 

[DTR]

tried to remove the diode from my alligator clips it burned my finger. Ouch the diode got so hot from just a few seconds of usage.

Did you not have the diode in a heatsink? If so then your diode is probably toast.

 

[Bionic-Badger]

The forward voltage drop of a diode increases as a function of the current passing through it. The 0.7V drop figure assumes small amounts of current typical in basic small-signals circuits. For power circuits the conditions are a bit different. Here is the V/I plot for a typical 1N400x series diode:

If you look at the plot, at 1.2A you're dropping about ~1.0V per diode, which is almost exactly what you're observing.

Also remember that 1N400x diodes are specified for a maximum of 1.0A continuous current. I know that when I used a set of 1N400x diodes for a dummy load I could smell the plastic melting and had to quickly shut off the power after each test. You should use a different series of diode for your high-amperage dummy loads. The 1N540x series of diodes, which can handle up to 3.0A of continuous current, should be sufficient. Heat sinking the diodes, or spreading them out for airflow is also a good idea.