Third boost driver not working....

[daguin]

Hi guys,

Sorry for the long wait, I was to busy to test the driver yesterday. The power supply I used previously is an ATX power supply I converted, and I used variable voltage output I built in (LM338 circuit - should be able to handle up to 8A) so I don't think there was a problem with the current output. Although I tested it with the batteries as well, I got the same results. The driver I tested now (and the one I'm hoping to use) was the one I bought from Odicforce, It should have a fixed output of 1A:

Diodes.....Input A......Input V....Output A.....Output V
1.............0.34A.......3.94V.......0.516A.........1.40V
2.............0.31A.......3.94V.......0.453A.........2.17V
3.............0.60A.......3.77V.......0.450A.........3.00V
4.............0.70A.......3.77V.......0.387A.........3.77V
5.............0.30A.......3.86V.......0.312A.........4.48V
6.............0.30A.......3.98V.......0.173A.........4.92V
7.............0.06A.......4.02V.......0.035A.........5.20V

Hope this helps! :thanks:

EDIT: I see the "table" didn't render well on my PC, hope it is still readable on your browser.

If I am reading this correctly, you are only putting an average of about 380mA into the driver, correct?

As said before, you are NOT supplying the driver with enough current

I don't work with computer PSU's so I don't recall exactly
However, I recall someone saying that there was a problem trying to use them with lasers

Hopefully someone else will pipe in with the why

In any event, your driver needs more current

Peace,
dave

 

[Cube777]

Thanks Cyparagon! Didn't know that... Sorry, I don't have access to a oscilloscope, only a multimeter.

@Daguin I only tested the driver with the ATX power supply at the beginning, all the results in the table was done with 2 of LarryDFW's 18650 batteries in parallel, IIRC, each capable of a peak current of 6A. There should be more than enough current available for the driver to draw.

 

[daguin]

Thanks Cyparagon! Didn't know that... Sorry, I don't have access to a oscilloscope, only a multimeter.

@Daguin I only tested the driver with the ATX power supply at the beginning, all the results in the table was done with 2 of LarryDFW's 18650 batteries in parallel, IIRC, each capable of a peak current of 6A. There should be more than enough current available for the driver to draw.

Then I too do not understand what your graph is showing

Try soldering an actual laser diode to the driver

Maybe there's a problem with your dummy load

If your driver is only supposed to be putting out 1A (if working) then it should not blow even an A-140 diode

Peace,
dave

 

[Cyparagon]

Possibly. You aren't using a 10-ohm shunt are you? I've made that mistake once.

 

[Cube777]

Thanks Daguin for the advice, but I've been saving up for this diode a long while now, and I'm dead sure that my dummy load is working perfectly. I've tested it with my other linear drivers and it worked perfectly. I'm sorry, but I can't risk the only diode I have, I've learned my lesson more than three times now, I'm rather being paranoiac this time around...

@Cyparagon I checked and it's definitely a 1 ohm shunt I'm using.

Anything else I can try to test the driver?

 

[benmwv]

I don't know whats up with that driver but i think its pretty much broken. Possibly from having a load voltage that is lower than the input.

Do you still have the fmt and x boost to test? They would both be a better option imo.

 

[Cube777]

I still have both of them, although both of them does exactly the same. I'll try and test both of them again today. So there's absolutely nothing else I can try (except risking the diode which I sadly can't do)?

 

[benmwv]

I think you should test the fmt. Since its buck-boost and has ovp (it does right foulmist?) it wont be damaged by the testing, which I suspect is what happened to the other driver. Plus foulmist can can help you out.

So, can you do another table with the fmt driver and post a picture of the setup?

Another thing I just noticed, there seems to be a lot of resistance between the battery and the driver. On line 6 the current draw was 0.30A and it was at 3.98V. On line 3 the current draw was 0.60A and it was at 3.77V. So a 0.3A increase in current caused a 0.21V drop. V=IR, so thats 0.7 ohms! So including internal resistance, there were 0.7 ohms from the battery to wherever you tested voltage. Thats way too much!

 

[foulmist]

if all the drivers are behaving the same i suspect it's a battery/power supply problem,

as ben said too much internal resistance.

check you cables too they might be too thin and heat up and add resistance.

i am pretty sure at least one of your drivers must be ok.

if you need help with the fmt shoot me a pm I will help you out :beer:

 

[BShanahan14rulz]

How are you making your input connections? clips, soldered wires, springs? The batteries LarryDFW sells are very capable cells, and should be giving you much more current than that.

Best conditions to test boost driver should be with a load with a higher Vf than your supply voltage. For example, if your battery is at 4.2V, you want enough diodes to burn off more than 4.2V. (Normally, you'd want your diodes' summed Vf to be approximately the same as your laser diode you plan on using. Here, we're more concerned with testing the driver than fine tuning its output with a particular diode.) Most folks assume 0.7V of voltage drop per diode, so use at least 7 diodes to get past 4.2V. 8 would probably be better, and would account for if teh diodes' Vfs as low as 0.55V.

Boost drivers can do strange things when you use them in the wrong scenario. Some don't work, some just DD, and I wouldn't be surprised if some break. I do still think that this is an issue with too much resistance on the input side, though. Best of luck!:beer:

 

[Cube777]

Thanks guys for all the help! I'm a little busy right now, will get to testing the FMT again asap and I will post the results. I have found that the 18650's have a larger IR than expected, although it's so small it can't have an impact on the input. I have silicone wires soldered to the driver which in turn is connected to the batteries with normal croc clips. I have found their not very good at handling current... I will try to get a direct connection to the batteries. Thanks Foulmist for the offer, will pm you if I struggle :beer: I will try up to 8 diodes this time and see if that helps with the Vf.

 

[benmwv]

No way, you should be using like 4 diodes! You have to account for voltage dropped on the resistor.

 

[Cube777]

Was just following BShanahan14rulz's advice of using at least 7 diodes or better 8

 

[Cyparagon]

Usually you do need to account for the drop on the resistor, but since these are boost converters and since the system does not appear to be sourcing much current, 7 diodes would be better at least until it starts working. Running boost drivers with a higher input voltage than output voltage will eventually damage them.

 

[foulmist]

the fmt drv is a buck/boost up to 6V input and 6V output.

you can't use 7 diodes unless the current is very small.

for 445nm you need to use 3diodes tops for high currents. they will give around 5V output

 

[Cube777]

Hi guys,

I tested the FMT, exactly the same results. I don't know if this helps, the driver emitted the distinct high frequency sound mentioned in the datasheet, although the input voltage is correct and the source is able to supply enough current. It emitted the same sound in buck and boost mode, also on 3 and 5 diodes.