This post is coming as a result of Tom E and Light Rider 's posts about modding this light , that is using a boost driver...
On my last chat with LR , he was about to mod the driver with a R050 stacked on top of the existing one , so a result resistance of about R025 .He was also planning to change the fly back diode ( in the original driver the diode is a "JA" one , 30V , 1A , with a very small footprint ...).
Having some time and the necessary electronics , I've started the job.., if I knew what was all about , I've never done it !...
First of all , you have to know that the 2 plates ( the charger and the driver , plus the electronic switch ) are connected with very thin wires , really short , that has to be folded in such a way , between the plates , to obtain a sandwich of no more than 7 mm !!! ( this is the depth of the space available !) . Anyway , you'll have to disconnect all of them , to be able to work on the driver...Take pictures , or make schematics , just to be sure you'll put everything back , as it was !
I wasn't planning to make a thread about this so, I took no pictures , but I'll try to explain , in plain words , what was all about...Sorry !
On driver :
I changed the diode with a "ss34" , the footprint significantly bigger , but removing some of the insulating paint off the copper traces , I soldered it in place .
The sense resistor , r050 , is located on the right side of the "MINUS LED" pad . It is very small ( unlike the sense resistors we are used to see on a driver !!!) .., but with a good reason , you'll see why , later...
After the diode change , I prolonged the led wires , connected its to the driver and powered , to be sure that all is O.K..., and it wasn't !!! No light...
Checking everything , I noticed that the " + Led " wire had the insulation compromised at the point where the led PCB was sitting on the shelve !
Here , I have to make an awareness point !!!
If you take out the reflector , that has threads , next time when you screw it back , to press the led , the reflector tend to rotate the led PCB and the wires will be cut as a scissors is doing , and a short circuit will follow.., that happened to me !
I was lucky that the sense resistor was small , and acted as a fuse , and the MosFet , was somehow , protected ...
At this point I decided to use a quality thermo adhesive for the led PCB , to prevent such events .., a good amount of adhesive , I used 2 drill bits (2.5 mm) to stop the pcb to rotate , and , with the reflector screwed back , I let it dry for 2 hours . In this way I was sure that the led will sit fit and will not rotate when the flash light will be assembled
Changed the sense resistor with the same value and size (R050) and powered up, again ... this time everything was good , all the levels working , the same 3.7 A at the tail and 1.08A to the led ! Time to " boost" the current !
An other R050 on top of the existing one and , before powering up , I had a moment of inspiration.., to check what are the specs of the MosFet ..!!!
It is a " 7423 " , in fact a SI7423 DN-T1-D3 , below I'll give a link to it's specs .
SI7423DN-T1-E3 Vishay Semiconductors | Mouser Romania
At the " Continuous Drain Current " , at 25 degrees the STEADY current is 7.4A , and at 75 degrees Celsius , the STEADY current is only 5.4A !!!...Wow...
Using 2 X R050 , in parallel , should boost the current up 2 times , meaning 3.7A X 2 =7.4A (probabilly less , due to the loses in traces and wires...) , but still too much , if the temperature of the Fet is increasing...
I set up a temperature sensor probe direct on the Fet capsule , to follow the temperature , and I powered the driver.., turbo mode ...
Tail Current = 6.8A , Led current =1.81A , so the efficiency almost 80% , anyway less than the original 85% , but normal thing , because of the increased current !
But , in 20 seconds , the temperature of the Fet reached 70 (!) degrees and rising fast !
I decided to stop and it was clear for me that , this transistor will fail if I'll continue to keep the setup with 2X R050 , in parallel ( meaning R025). Time to change the sense resistor to a 3X R100, parallel ( about R033) , meaning of an increase about 50%.! Two minutes later , with the resistors in place , I powered up again , hoping...
Tail current = 5.1A , Led current = 1.35A , efficiency 79% !!!.., transistor temperature 64 degrees , steady at 10 minutes... Not bad , but looking to the led current increase , is not much ...somehow disappointing... I have to admit that is a little brighter than before , but not with much , to make you say ...WOW !
After that , took me 3 hours to put everything back , with those tiny wires .., I had to secure the driver in place with a drop of glue , in order not to rotate when you insert back the battery tube...
Now , on turbo , is becoming hot in 5 minutes (58 degrees ) , but is holding this temperature even after the stepping down...
Now , you can decide if is worth so much work , risks of something going wrong.., if it was for me to know before , I'll remain with the stock one , is good enough...
But it is up to you and , as crazy as I know some of you are , you will do it , just for the sake of art...!!!
Feel free to ask any questions , I'm sure I didn't cover everything...
Cheers !
