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2W SKYRAY SR-5 With Modded Single 1.8A Microboost Driver

DTR

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Alright here is the follow up on lasts nights build. It did end in dissapointment but I am not sure if it is a black mark agains the driver mod.

So I tested the driver after heatsinking it. I did a six minute run. I also set this one a tad higher which could also by why I ended up crying at the end of the night.

Anyway It seems pretty stable so I decided to go ahead and build the unit.




Now here is the rub. I played with it for about an hour and everything seemed to be going good. Then I set up for a video test. I wanted to do another six minute run. So I got it going and was watching it for the first couple of minutes and walked away. When I came back it was LED.:eek:

So I reran the vidoe to see what happend. It appears at about 4 minutes(You can see it at 3:30 into the video) the driver started to go into thermal protection mode and normally I would have turned it off but I was not paying attention. So now I am left wondering if I had not left it on for a while in thermal protection mode if it would not have died.:thinking:


 
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rhd

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I think it's possible that what is happening, is you're effectively setting a near 0 ohm resistance across whatever set of resistors this driver uses for current setting.

In essence, this would cause the driver to try and try and try to boost voltage until it sensed the FB voltage drop it expecting. Of course, with a near 0 ohm resistance, it would never actually achieve this voltage drop.

In terms of the rather remarkable boosting ability (1.8A), this isn't entirely unreasonable either. If you had created a near o-ohm resistance across the set resistors, then you wouldn't be dropping as much voltage (or really much of any voltage) for current setting. Depending on the IC's FB voltage, this might mean the diffrence between a normal Microboost boosting from 4V to 5.25V and this modified one boost much less, from 4V to say 4.75V. That's a small difference in absolute terms, but a huge one in relative terms. That's a whole lot less boosting.

So probably, that 1.8A output current isn't a true constant current, but more a product of the IC's maximum switch current. As such, the ultimate death might have merely been a product of this setup being able to spike a bit above 1.8A output when everything is nice and cool. Maybe one of those spikes was a bit too much.
 

jayrob

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Yeah it's hard to say it was the driver, or just the fact that the diode was getting pushed to the max and would have killed a diode at that current with any driver. (like a P3 for example)

In any case, pretty cool that your getting that stable of output from a tiny little MicroBoost driver!
 
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drlava

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Hi, nice build, nice looking beam, too. RHD is correct the driver was running flat out at the 3A switch limit, this is why that value didn't change during your test. I'd suggest you try this instead, replace the large resistor on it with one of these

Digi-Key - RHM.13SCT-ND (Manufacturer - MCR25JZHFLR130)

, turn the pot all the way down, and only set the jumper on that resistor. This will start you off at about 1.5A, in regulation (when the battery is new and fresh), and then you can experiment turning the pot up slightly (or jumper the other resistors) to see where you can take it from there. The MicroBoost is a sturdy little driver, glad to see it put to good use/abuse :)

edit:
another thing you can do to eke out a little bit more performance at the sacrifice of the reverse battery protection is to solder jumper across the 3 lower pins (on the side of the 4700 resistor) of the black 3-legged device in your last photo.
 
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benmwv

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Yeah, in the initial testing of the lm3410 driver I accidentally shorted across the sense resistor and it managed to pump out enough current to kill an m140 :(

The lm3410 even has a bit less switch current at 2.8A
 

DTR

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Hi, nice build, nice looking beam, too. RHD is correct the driver was running flat out at the 3A switch limit, this is why that value didn't change during your test. I'd suggest you try this instead, replace the large resistor on it with one of these

Digi-Key - RHM.13SCT-ND (Manufacturer - MCR25JZHFLR130)

, turn the pot all the way down, and only set the jumper on that resistor. This will start you off at about 1.5A, in regulation (when the battery is new and fresh), and then you can experiment turning the pot up slightly (or jumper the other resistors) to see where you can take it from there. The MicroBoost is a sturdy little driver, glad to see it put to good use/abuse :)

edit:
another thing you can do to eke out a little bit more performance at the sacrifice of the reverse battery protection is to solder jumper across the 3 lower pins (on the side of the 4700 resistor) of the black 3-legged device in your last photo.
Awesome. I will order some of those resistors and try it when my next batch of Microboosts gets here. At least at this point we know we can heatsink this driver and it will run @ higher currents. Now just to work out the best way to set it up to do this.:beer:
 




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