Increasing the Output Amperage of a LED Boost Driver

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HyperSpeed

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I have accumulated quite the supply of flashlight drivers for LEDs. One which strikes me as very interesting is in a setup that currently drives 6 total 3V LEDs in series from 3S lithium.

OK so here is where things get muddy for me: I can lower the current-sense resistance of the driver to tell it to output more power. At some arbitrary amount near 0.135 ohms on the sense, the driver basically stops working. I assume I am exceeding ability of some component and potentially over-heating or instantly frying (LEDs are completely within spec power). It is OK, as I have many of these drivers and wanted to experiment with the first one.

What my mind is so far attempting to deduce is what component(s) on the board appears to be creating the power conversion from (input amps) to higher output volts--as the boost philosophy goes. It appears board components with position addresses beginning with 'Q' are N type MOSFETs. There are 4 on one driver.

What I realized is that I have a few newer PC motherboards headed for junk piles, and they appear to be gold mines for such scrap components as MOSFETs.

Is someone around who is able to confirm if in fact the MOSFETs are the component to upgrade, to increase amp output and thus total power ability? General ideas or guidelines of how you would go after this mod would be highly appreciated. I am able to reflow solder components, or hunt down whatever it may be, or upload photos of whatever you would like to see.

Thanks for any advice towards tackling this project! :wink:
 

HyperSpeed

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Maybe I need to reword this a little.

In a "boost" driver circuit design, the voltage on the output is greater than the voltage on the input. What determines how great the difference between the two can be? In other words, is the driver's ability to boost voltage determined greatly by a single limiting factor, such as the rating of the MOSFETs?
 

rstaff3

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Well, I know nothing of the drivers you have but you need a mosfet that can handle the voltage that you want to switch and then make sure the driver can drive said mosfet. Ap notes may help.
 

bill_s

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If the design is compact, it probably doesn't use any discrete FETs. At any rate, a PC board won't have any, power supply probably, but low current high voltage.

In a boost circuit, the FET's go between an inductor and ground, seemingly trying to short out the battery, which perhaps is a clue. If there is a special purpose IC, the datasheet could include the circuit. Possibly someone is familiar with the specific popular circuits/ICs, I know the generalities but would need to analyze the whole actual thing (or start over).
 

NAR29996

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Generally speaking, if you can increase the switching frequency, you should be able to increase the output.
 

XolveJohn

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Is it all in one chip, or are there discrete parts. It is probably going into current limit. Trying to increase the current past that might blow the FET. Just use 2 chips in parallel!
 
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