Efficiency measurements of a few drivers

Flashlight Modding and DIY Parts
1

Sometimes when I disassemble a flashlight I measure the efficiency of the driver, here are a few :

Fireflies E12R :

https://i.imgur.com/B5HRWRh.png

Uses the TPS62480, a dual phase synchronous buck converter with integrated switches, 2.5MHz switching frequency.
SI7655DN Reverse polarity protection PFET, should be around 4~7mΩ

Driver pictures courtesy of Sunnysunsun

Skilhunt H04 :

Asynchronous buck driver.

Zebralight SC64 :

Uses the TPS61088, synchronous boost converter with integrated switches, set at ~600kHz switching frequency, ~12V output.
Coilcraft XEL 4020 1uH inductor, 14.6 mΩ
SiA447DJ RPP PFET, should be around 12~16mΩ

Zebralight SC64c LE :

Uses the TLV62085, a 3A synchronous buck converter, 2.4 MHz. I thought the driver would be 3A but it’s 2.8A instead.
Coilcraft XEL 4020 1uH inductor, 14.6 mΩ
2x2mm RPP PFET, 13.5~15mΩ.

Zebralight H600c/d mkIV :

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

Zebralight SC700 :

Uses the TPS61088, a synchronous boost converter with integrated switches, set at ~750kHz, ~6V output.
Coilcraft XAL7030 1uH inductor, 5mΩ.
SISS23DN RPP PFET, about 4~6mΩ.

Zebralight H53/SC53 :

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.

Convoy FC40 22mm driver :

Thrunite T1 :

Uses the MP3429, 600kHz synchronous boost converter with integrated switches, ~12V output.
6030 0.68uH inductor
AON7423 RPP PFET, <5mΩ at –4.5V, <6.5mΩ At 2.5V
Rsense = 150mΩ, Vsense = 150mV

The efficiency isn’t as good as it usually is with this converter, it has quite thin traces, fairly high current sense resistor and too low inductance.
Input capacitance is quite low (one 0805 capacitor), I had to add a bulk capacitor for making the measurements as it didn’t work properly in turbo with my power supply.

Acebeam E70 CRI (FC40) :

Again it’s based on the MP3429, 12V output for this version, I believe the XHP70.2 version is 6V.
What is interesting is that they use a second higher value (0.25Ω, 2x 0.5Ω weirdly) sense resistor for the moonlight mode, like my drivers and Zebralight’s (usually they use 3 or 4). The low value high power sense resistor is 10mΩ + the ON resistance (3mΩ) of the NFET (AON7520) used to switch between the two.

The turbo output starts to decrease below 3.5V and reach ”high” output around 3.2V, this isn’t a limit of the boost IC but a firmware limit.

The reverse polarity protection PFET is an AON7423 (3333 package), this seems to be a common one, seen on Thrunite, Convoy and Acebeam drivers.

Inductor is 7.5x6x5mm, 1uH.

The efficiency is not very good in moonlight low and mid 1 because they decided to use FCCM (fixed frequency PWM) instead of PSM or USM (usually this one is usually used) so relatively a lot of power is wasted at low output, bad choice.

Another strange choice is the tantalum capacitors for the input, I thought they were more expensive than MLCCs and two 1206 MLCCs would have been adequate here.

I forgot to take a picture but there is an aluminium post in the driver cavity above the boost IC with a thermal pad to improve thermal dissipation, that’s a very good decision especially with the fairly high output for this converter.

Noctigon KR4 12V 2A :

It uses the MP3429, 600kHz synchronous boost converter with integrated switches, ~12V output.
6030 1.5uH inductor, 11.5mΩ (Haukkeli’s measurement)
RPP PFET WSD20L120DN56, 2.9/3.3mΩ at 4/3Vin.

I also measured it at 2.54A after increasing Vsense from 40mV to 50.8mV.

The D4Sv2 and D4v2 boost driver use the same components and will have the same results.

Two of my drivers for comparison :

https://i.imgur.com/H1yUVoh.png

11 Thanks
2

Wow! Glad you shared! Have any fireflies? : )

3

You’re welcome.
The first one is the Fireflies E12R, but all their new models have the same driver.
Edit : well not all of them, but all the ones with “High efficiency 6A constant current buck driver (>90% efficiency) with FET Turbo” : E12R, E07x pro, NOV-MU, T9R.

4

Great to hear, saw the e12r but was focusing so hard on my next buy, E07x pro, that I forgot. Seems out of stock, and seems impossible to get for an extended time.

5

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.

6

Merci beaucoup pour les test et résultats!

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

7

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.

8

Wow this is such an interesting and useful post! Thanks for testing and sharing!!! :+1:

9

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.”

10

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.

11

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
12

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. :smiley:

13

Thanks for the compliment :blush:

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.

14

That is pretty impressive being basically self-taught. :+1:

15

Great work, thank you for sharing!

16

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 :slight_smile:

17

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.

18

Thanks, nice info.

19

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.

20

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.