So I found today a very odd problem with the LM3409 Buck driver
Its related to the voltage regulator, it seems in this case 10 Ohms resistor was to big get the LDO in a stable regulation,
it had a voltage drop over C1 from 16 to 10.5V, which is very bad, the resistor should decouple battery and LDO input voltage from spikes,
but the battery side looked pretty clean while the LDO side had every 20ms a big drop from the LDO probably resetting
output voltage had about 1.4V ripple on about 70% of the ramping very low working fine, then at a level it started
resulting in an unstable max. current as the current control voltage was not stable at 5V
Replacing the LDO and trying to solve probably capacitor issues replacing them as well did not help
I lowered R1 from 10 to 4.7Ohms this cleared all ripple on the LDOs input and output side
I recommend if you can solder SMD to do this on all drivers add a 10 Ohms resistor above R1
Interested in one of the next-gen super high current buck drivers (like the CFT-90 driver for the BLF GT). Intended application is driving 7 ~6v Nichia 144 LEDs in parallel, from either 4s or 2s2p (which would work best?) in an SRK style light. If there’s a driver in this series that fits the bill, please put me down for it.
It’s hard to say. The D4 bin has a tolerance of plus or minus 7%. Assuming you had two that put out the same lumens at the same amperage, you’d need a lux meter that read the different color temps the same. Most of the inexpensive lux meters seem to be more sensitive to CW.
If we are comparing a Buck driver to a FET driver, the FET is always more powerful. It delivers as much power as the batteries can give and slowly tapers off as battery voltage starts to go down.
The buck driver starts off at a lower amperage and power level but maintains steady output until the voltage gets too low to stay in regulation and then it starts to either taper off or step down to a lower power level.
Honestly, Lexel makes so many drivers they are hard to keep track of. Once he see this question I’m sure he’ll go into more detail.
I know Texas_Ace prefers the FET driver to run xhp70.2, but Lexel prefers to run it on his buck driver.
According to the info I can find on Lexels threads, his buck driver can do 7.5A@12v (you convert the battery carrier from 6v to 12v).
A FET driver can pull from 9 to 11 amps at 12v depending on the emitter, etc…
on my Buck drivers I went right from the beginning on all with
G Ground
S Switch
L for indicator LED
later LS was added as permenent LED
yes I am too busy to keep track and got no notification that this topic was updated
The new MF02S buck driver has only about 0.2V more voltage drop over a DD driver, but it is limited to 8A from the voltage sense resistors
on the middle currents it gets of course more efficient
anyways 6A is sort of the highest current I would do to a XHP70.2 having very high output
and not going to the limit of the LED where you gain very little brightness with tons of heat
MF02S (originally MF02 XHP70.2 mod) driver is out now a few months
basically there had do be made a few improvements and parts change to get it more efficient
as well get some ringing problem on the LDO fixed that occured on higher currents
MOSFET was changed to a far better one
less voltage drop 5.5 vs. the old 12.8mOhms,
It has 1/4 of the switching losses as it switches faster
I could go up in switching frequency a lot which was reduced on the first XHP70.2 mods
total loss compared to old 1/3
Inductor value cut to half now 2.2uH with new FET and resistance as well (XHP35 has 10uH, old XHP70.2 4.7uH)
Output and Input caps sustained to handle the more current
Let me give it a try as I modded today for someone else a MF02S
I am bad at making videos but I post it anyways
actually the PSU voltage meter uses calvin clamps so its reding on contact points on driver to compensate losses on the wires, even if they are 2.5mm²
Measurements
Turbo (measure 3 times and used average later as in video the clamp meter was not prcise)
Input: 15,15V 5.4-5,44A
Output: 13,44-13,51V 5,70-5,74A
Efficiency: 94,4%
I also changed the calibration resistor to get to 6.09A later and did again 2 measurements
15,11V 5,8A
13,6V 6,09A
94,5%
fully charged VTC6 should give this voltage
16,17 5,37A
13,55V 6,04A
94,25%