comfychair-inspired quick+cheap+lazy single-sided 17DD FET-driver (poor man's nanjg92)

All credit for this version goes to Comfychairs great work in the NANJG-92 thread and tutorial. Unfortunately at the moment all the great pictures are gone from his tutorial :-( Edit 2019: comfychair has since long restored his pics :THUMBS-UP:

His NANJG-92 driver still is the quickest and cheapest 17DD driver you can make to date (and with just using a solder iron, no reflowing needed), but for the true cheapskates that are even more lazy (e.g. me) I just made an even cheaper 17mm DD FET-driver.

I had to fix a quick wow-mod for the 17-year old son of a friend of mine who had a cheap SmallSun C8 clone with a XR-E that was broken. I had a dedomed XP-G2 on a Noctigon in the parts box (my parts box contains some fine parts ;-) ) and this C8 needed a 17DD FET driver too to get the light to close to 100kcd and make his daddy die of jealousy :evil: . The last one I made was a wight's A1-17DD-s08 board v24, I scavenged the MCU from a AK-47A driver for it. But I knew from making a couple of NANJG92 drivers before, that the other way around is quicker and cheaper. So I tried to be even more greedy by using a $2.20 no-brand AK-47C from Banggood, and a 70 cents LFPAK56 size PSMN3R0-30YLD FET from Mouser, the one used for wight's 17DD drivers. But there's more similar FET's around, I'm not an expert (Rufusbduck suggested this PH4030AL NXP Trans MOSFET N-CH 30V 100A 5-Pin(4+Tab) LFPAK FET from Ebay, but I'm not sure it was tested anywhere Update EDIT: they work, see post #13 #15 #22 thanks to Major for some measurements)

Anyway, using the solder iron, I zapped the three 7135 chips and fitted the FET upside down comfy-style, one leg soldered to a pad going to the MCU, two of the three parallel batt-minus legs soldered to the minusring (I scratched away a bit of the solder mask to make both legs stick). The third batt-minus leg is just hanging around doing nothing. The led-minus wire was soldered on top of the FET. This FET is small enough that no filing is needed to make it fit. I did not bother using Kapton tape to mask unwanted solder pads, like comfy did in his tutorial.

Voila, a 3-dollar-3 minutes 17DD single-sided FET-driver! It works like a charm it seems from brief testing it outside a flashlight, it is fast-PWM five modes with blinkies (17-yr-olds like that). I just have to build it into this boy's flashlight now. I will report any failures, but I don't see why it would.

(stereo image)

Good job, Do you had to reprogram the MCU so it can control the FET ?

Nope, I know no programming and I'm comfortably unaware of problems arising from using FET's instead of 7135 chips.

I have no idea on what you described but it works, its cheap and the end user beats his dad. It doesn't get any better than that.

Nice work. Reprogramming resets the lower modes lower since pwm’ing DD results in more avg current than pwm’ing the output of a fixed number of 7135’s. :stuck_out_tongue: to ignorant bliss.


I really like the dual mode setup…the LOW>MED>HI OR LOW>MED>HIGH>STROBE>SOS…I also believe they have upped the PWM so it’s no longer flickery to the eye

Brilliant job like it a lot. Thanks for the heads up on the eBay fets, have ordered presume they are the same size?. Strangely searching on eBay (worldwide) doesn’t bring them up but going through your link works fine, stupid eBay App. Mouser shipping is kinda prohibitive to the UK.

It is not that I know for real that these ebay FET's work, they are mentioned by Rbd in wight's 17DD thread as perhaps being suitable as well, wight could not see anything wrong with it. So if you could report that they work and work well, that would be helpful. (anyone else used this FET?)

Thanks for adding extra information on this nice Nanjg92 mod djozz. The main problem seems to be getting these high current capable FET’s.

Does anyone know why comfychair quit BLF all in a sudden? He is one of the great contributors in this forum and I hope he is fine.

While waiting for the ebay FETs from china,
Ph4030 PDF
I ordered one of these from ebay uk, it arrived today,
A quick test shows it has very low resistance only 1.55mOhm @ 3.5v Vgs. But it has twice the gate charge, at 32nC, of the fet in the OP, so it may cause problems with the ATtiny. I’ll fit it to a driver next week and report back. My first DD driver is imminent!
Oh and this fet is really thin and tiny they say it can switch 100amps that is crazy crazy for something so small.

The emphasis of this thread was cheap, right? I was browsing over some old dx-pages, and came across the NANJG ak-47 even cheaper: 2 boards for $2.89 . That makes this driver $2.15 :-)

Thanks for the link djozz. I am gonna order some of these and the only uncertainty is about the FET though.

Major has the 'ebayFETs' on order and I ordered them as well. I will make one of these and test :-)

I received the FETS from Ebay (link again, they are 90 dollarcents a piece when sent to the Netherlands ) and tried one out on a AK-47 driver, soldered like in the OP. It gives proper modes and a protected NCR18650B (not a high-drain battery) on an old-gen XM-L bare on an aluminium non-dtp board gives 900+ led-lumens at start up in the sphere. Sounds at least close to direct drive to me :-) I will have to confirm the FET's quality with a proper mod and current and output measurements, but it looks promising.

If it’s good then I am gonna order a bunch of them. Thanks for the effort djozz!

Ebay ph4030 FETs arrived today. Only 8days from Hong Kong! Preliminary test looks good.
On paper they appear the same as the Vishay 70n02 fet that was popular. I measured Drain Source resistance 5.1mOhm at 3.5v gate voltage. Not as low as 1.55mOhm of more expensive NXP 1R2-30YLD, but still low. Gate charge is low and they are Cheap and Easily available, and fit well along side the attiny13.
Thanks djozz ordered a handful of the DX drivers.

Thanks for the info, Major.

I'm actually surprised that this thread does not attract more attention. It is not that I invented the wheel (comfychair did), but this easy single-sided driver version has everything that wight's beautiful 17DD single-sided driver has (single-sided, DD, low voltage protection, reverse polarity protection, great direct electrical connections from battery to ledwires -better than a 105C-, programmable MCU) but it comes with extra's:

-dead cheap

-only two parts have to be sourced which are available for everyone around the globe

-you can flash new firmware, but if you don't it comes ready with NANJG stock firmware which is not the worst of UI's (high freq.PWM, alright mode groups)

-if you keep the stock firmware it is an easy three minutes build with just a solder iron

But I admit it does not look as handsome as a wight-design on an Oshpark board ;-)

At least it DOES attract my attention. :slight_smile: I know what these things can do, simple yet effective and thanks for helping us to document these information here again.

The only “problem” for me is I am not sure which FET has the low resistance which I can access to. Thank you Major for reporting this to us and I am going to order some of these later.

You got my attention - but as I'm new to modding and electronics, I don't understand half of it :-P

I sometimes start reading topics as they sound interesting, but quickly have to give up because of a lot of technical stuff, and a lot of abbreviations ;-)

Yes, sorry, I'm guilty of abbreviations as well, makes the writing easier and the reading tougher :-(

Perhaps it is nice if someone would write a short history of how the different BLF-drivers have evolved.