FYI: Mission Accomplished!!!
Excuse / forget the last few posts about swapping out components or designing a custom boost converter board "cuz it just t'ain't necessary" my friends!!
This is the secret solution: It's a tiny mini-boost converter for one dollar but rated at 2 amps
(we only need about 0.5A
) and easily fits into the former CCFL inverter space... but is about 1/3 the length.
There are other parts to fill the remaining space:
1.
2 IRFZ44 power Mosfets:
One, #1, for constant current LED protection (which the mini-boost converter lacks and on 12 volt
AC power will fry them but not on battery 8.5 volts
); its source pin connects directly to the right/negative lead on the Jornada screen ccfl connector/tab.
The
other #2 is for the dimmer circuit which gives amazing Low levels never possible
with any CCFL and also delightful Brightness for outdoors
(much brighter than my new Laptop screen as I post
this
)! This is placed in series with the first #1 Mosfet . It's gate is connected directly to the J680
dimmer lead the thin center tap.
2. A 2N3904 transistor combined with a 100k and a 3.3 ohm resistor to bias the base, which in
turn feeds back to the #1 Mosfet gate to prevent over current.
3. I added a
tiny smd 3 Amp self-recovery fuse to the left/positive lead on the J680 ccfl connector tab which connects directly to the 32 LED strip replacing the CCFL tube
(to protect the Jornada from any LED or boost converter meltdowns
).
Something very interesting is occurring between the 2 Mosfets... when I first set up the circuit without the dimmer circuit mosfet... the constant current Mosfet would get quite warm on max brightness. Now, with both in series and dimming working well
(although reversed from ccfl keys
) both Mosfet s actually feel cooler than ambient temp... some sort of peltier like effect going on. This leads me to think I can increase the current and brightness further, although it is very readable outdoors unlike the essentially black screen I see with the dated ccfl backlight on my J720
So I'm done tinkering here, just need to mount it all in the case, will follow up with photos, schematics, and detailed "how to" info.
Really really nice... super bright and super dim... Like Never Before! For much less than $15 in parts
Joval
Edited by joval 2022-03-25 1:08 AM