Hi guys,
I've watched quite a few of these EEV videos on youtube. Good stuff. Decided this was the place for assistance.
I have used original schematics to "clone" an old sega mainboard just for project as I find it enjoyable to muck around with kicad and learn more about electronics.
I'm basically ready to measure out some mounting holes and add the power circuit but I don't want something as simple as - input cap - regulator - output cap type thing
I want reverse polarity protection for one thing. The original board is centre negative.. mine will be centre positive (I use aftermarket supplies and a little section of cable to swap polarity anyway)
Also the factory DC packs are rated at 9 but do just off 14v with no load.
I found a crowbar schematic with all the bells and whistles and made some adjustments
original:
http://www.electronicecircuits.com/electronic-circuits/7805-5v-1a-regulated-power-supply-with-overvoltage-protection-circuitmine:
This was considered overboard by other people, it is also a little heavy on components...
2 of the original supplies are here:
The one diode in series seems to do the trick for reverse polarity protection.
Nothing gets fried when using the wrong adapter on the original boards, including the regulator.
A lot of sites are saying the diode between the input/output of regulator is not necessary, this is just for reverse discharge protection from caps?
Also concerned about noise as the originals seem to have ferrite beads (discontinued: FBA04VA600VB-00)
I was looking to substitute for: BL01RN1A1D2B
BUT, is this really necessary??
I've also read having the ferrite bead on the ground connection is not a good thing either?
Having a super clean supply is a priority, as the original boards are known as noisy, although mine is for RGB output only and doesn't contain the extra video encoding circuitry and clock line which would attribute greatly to the noisiness of the board.
So do I keep it simple, copy the original schematic across, with ferrite beads? I wanted to use an LM2940CT in replacement of the 7805 as it's a cleaner supply and its LDO so I can run this down to 6v input if i wanted to.. less heat.
BUT then i found the MIC2940 which has built in reverse polarity protection.
One thing that confuses me is does this protect every IC on the board, or just the regulator from being fried? Seen as how the original boards can handle reverse polarity and nothing is hurt surely I'm going a little overboard??
I know i could just smash on any simple, cheap as chips 5v supply and it would be ok.. but I want to ensure the output never goes over ~5v and fries my IC's, and I want super clean! The proprietary IC's are hard to find and aren't cheap yet alone the rest of the components.
Cheers