# Efficiency measurements of a few drivers

Unfortunately it doesn’t look good, both the buck converter and charger IC look to be out of stock with long lead time at major electronic vendors, especially the buck IC with more than one year lead time, they probably should have redesigned their driver with parts with better availability.

Edit : Ah it looks like they supplied banggood with NOV-MUs so they do manages to produces some drivers.

Merci beaucoup pour les test et résultats!

I would be super curious to see the same test results from an Emisar Linear driver.

These are always interesting to see. Could you shed some light(pun intented) from which background you jumped to designing drivers? Where have you accumulated your knowledge of electronics, if you don’t mind me asking? I’m just curious, you can PM if you don’t want to share publicly.

Wow this is such an interesting and useful post! Thanks for testing and sharing!!!

I’ll echo the posts above. I’m glad to see great contributions by knowledgeable individuals on here.

I hope you can test a cheap Convoy boost driver to see if it is also quite efficient.

I guess for a linear driver, the efficiency can be approximated without direct testing? Knowing the forward voltage and battery discharge curves should be sufficient to know how much power needs to be “burned off.”

De rien !

A linear driver is effectively a variable resistor, current in = current out, so the efficiency is just Vout/Vin, i.e. Vf/Vin , hence the efficiency is low when the cell is full and the Vf is low, e.g. low/mid current and/or multiple LEDs.

The efficiency is at its maximum (for a given current) when in dropout, meaning the input voltage is not high enough and the current starts to decrease, then the losses are just due to the resistance of the driver in its minimum resistance state. Which if I were to guess must be something like ~15mΩ for the Noctigon linear driver (just the board, not counting springs and wires), it’s the Rsense (10mΩ) + traces/vias + FET.

So if we take for example a D4v2 with 4 SST-20s, say with a sustained current of 2A, that means a Vf of ~2.8V and an average Vin of ~3.7V (30Q), that gives an average of ~2.8/3.7= 76% efficiency.
At 5A, roughly 3/3.6=83%.

The E12R driver would do something like 93~94% at 2A and ~91% at 5A in average. My buck driver 96~97% and 93~94%.
Ideally we would count the input side resistance from the springs and cell, which gives a slight edge for a buck driver since it draws less input current.

Another example that this time would give an advantage to the linear driver : an SFT-40 driven at 9A in a big host, used nearly exclusively in turbo, which would be regulated only for a small amount of the cell’s capacity, so it’s quickly in dropout and then the losses are just from the low resistance of the driver.

I don’t have any DC-DC convoy driver unfortunately, but they seem to use high efficiency synchronous converters.
Agnelucio tested the XHP35 driver here , it’s based on the MP3431 just like my boost driver. Just a note, he converted it to 6V and bypassed the RPP PFET, so his numbers are slightly better than stock.

No background, just high school electrical knowledge, which I refreshed by doing a few Khan academy courses, plus some more beyond high school level.
I searched about making a constant current source and found circuits with a FET and op-amp, which I recognised in a couple of drivers, like Convoy and Noctigon, studied a bit about the op-amp, read a few app notes and applied that circuit to DC-DC converters.
Then learned how to use Kicad to design PCBs, spent a lot of time reading datasheets and searching for good components, and a lot more for prototyping and testing.

1 Thank

Cool. Obviously you are good at building on a base of theoretical knowledge learned from school.

Sadly, here in Finland, it seems only diplomas from schools are worth anything. In my opinion it has started to diminish the value of self learning and studying.

In job markets self learned studies or skills don’t seem to matter much. You need to have some kind of diploma from academic studies, before they are considered real skills. Otherwice they are just considered hobbies.

That’s quite depressing way to say, that you are doing great job and methodically getting better at it every day.

Thanks for the compliment

Zebralight H53 :

Uses the LTC3539-2, a synchronous boost converter with integrated switches and low start-up voltage (0.7V), 2MHz switching frequency.
~5x5x4.5mm ferrite core inductor.

I checked several times the measurements for a mistake but in the end the efficiency appears to be just… not great.
Though given the high resistance of the integrated FETs it’s not that surprising, ~90mΩ for the low side NFET and ~180mΩ for the high side PFET.

Edit : H53, not SC53, although I’m pretty sure they use the same driver, same lumen rating and there is a hole for a wire coming from below the PCB for the flashlight layout.

That is pretty impressive being basically self-taught.

Great work, thank you for sharing!

Interesting to see how inefficient the SC53 is compared to the other Zebralights that were tested.
Skilhunt H04 offers very good value.

Efficiency on the E12R and SC700D is the reason I always buy Buck or Boost lights

Zebralight H600c/d mkIV

Uses the TPS61088, synchronous boost converter with integrated switches, set at ~700kHz switching frequency, ~6V output.
Coilcraft XEL or XGL 4020 1uH inductor, 14.6 or 9mΩ
I couldn’t find the ref of the RPP PFET, but like in the SC64 it’s a 2x2mm package, 13~17mΩ.

Note that this is the driver only, the H600 series have a very high resistance negative spring around 50mΩ which substantially lowers the efficiency on high modes.

Thanks, nice info.

Wow the Fireflies driver is impressive! I’ve been using the Nov-MU on a daily basis and absolutely love it. Too bad they seem to be having difficulty sourcing components for the driver for the past year.

It’s pretty good yeah, what is disappointing is that there not enough input capacitance and when a higher DCIR cell is used like a 50E or an older cell then the output can be unstable, which when it’s pronounced will lower efficiency, output and generate noise which several people have reported, it does it with my P42A that is not even that old.
It uses the amount of capacitance suggested in the datasheet (2x 10uF 0603) but in my experience of building drivers the suggested input capacitance for buck converters is usually not enough.
I added more caps, two 10uF 0603 stacked and one 0805 22uF farther away by removing some solder mask, but I haven’t reassembled it yet to fully test it.
Another (small) issue is the max current of 5.5A, the traces resistance on top of the sense resistance were likely not taken into account when deciding on the Vsense.

This data is really interesting, thanks for providing it. Seems like the E12R and SC700 do quite well. Do any of the other ZLs have the same high resistance negative ground spring issue, or is that just the H600? Does SC600?
SC64w HI also seems pretty decent. Do you know how SC64c LE would do? I wonder, since I would guess that would be a 3V buck or buck/boost, in contrast to the boost used by the other 3 models here.

Why do you think some of these drivers have lower efficiency than some of the driver designs I’ve seen around here on BLF (such as yours)? Are there particular design limitations involved for these companies?

Any chance you have and could test the timeless Noctigon Meteor M43 flashlight driver?

hm
all that means to me is, i might need to charge in 8 days vs 8.34. with one light vs another. sometimes. if the LED efficiency doesn;t invalidate the driver efficiency…

?

wle

thefreeman, thank you for this!