Hi guys
hope someone could give me advice if what I would like is possible to do.
I would like to get a bit more amps from this Sofirn SP31 driver, I can do that by lowering resistance on current sense resistor (R075)
but even at stock value those 3 pin chips marked with yellow arrow (3400) are heating pretty fast and pretty uncomfortably.
My question is, would it help if I stack one (or maybe 2) additional 3400 chips on top of existing ones?
I presume those are FET-s and that stacking additional will lower the load per chip!!!
Since that looks to be a buck driver (note the inductor), those FETs are operating as switches, rather than variable resistors. Their resistance when switched on should be in the neighborhood of 40mOhm. They are almost certainly operating in parallel, so their combined resistance is 20mOhm. This is a switching regulator, and I believe that buck converters usually switch on the input. I’d guess then that the average current through the pair of FETs is less than 3A. At 3A, the voltage drop will be ~60mV, which works out to 180mW, which is well within specs. At 6A, the drop is 120mV, which works out to 720mW. Still within specs, though it will be quite a bit warmer.
Paralleling more FETs isn’t going to help much, not enough to be worth doing, I think. Even if you halve the resistance of the sense resistor (and roughly double the output current), the sense resistor is going to be dissipating ~2x as much heat as the FETs. Also, with more FETs in parallel, their switching time will likely increase somewhat, which could actually result in more heat.
As currents increase, the inductor will also be running a lot hotter. In fact, even now, I wonder if the FETs are really the main source of heat.
I’d suggest messing with the sense resistance and observing the resulting temperature increases before worrying about the FETs or any of the other components.
Hi eas, thanks for the input.
I am not an electronic expert, as you can see but what you say sounds right and logical to me :+1:
so I just added 2 x R100 resistors in serial across R075, got about 3.8A, will test it few days like that, if it survives maybe Ill go even higher
3.8A is better than 2.7A stock but in general 3.8A is not much.
Thanks
but what you say sounds right and logical to me :+1: