Tuesday, December 4, 2007
Back to the drawing board...
After some critiquing by a few N&V forum members more knowledgeable about power supplies than myself (which is likely to be all of them) I've decided I need to do some redesign on the PSU.
I reworked the design a little to reflect my current implementation (the direct battery line for the DTV's screen) and after some charging and testing I've determined:
1) the 3.3v regulator needs to run off the battery directly, not one of the 7805's... it generates a load for the 7805 which heats it up something fierce.
2) my current NiCd cells are probably shot. They don't hold a charge for very long at all.
3) my R1 resistor is too large, as I calculated the charge current incorrectly.
4) I would get a lot more efficiency using a switching battery charger controller like some of the ones offered by Linear.