The 7805: Am I missing something?

[Bibin]

So, a lot of these older consoles have a 7805. Many of these get their operational power from nothing but the 7805. As far as I know, the 7805 will output 5V.

Why is it that everyone seems to insist on feeding 7V to the 7805? It seems that you can feed it 5V, and bypass the 7805 altogether (for systems that just rely on the 7805 output), like I did for my FC Twin. Why should I be feeding more into the 7805, wasting voltage and generating heat, other than the convenience of 7.x volt batteries?

 

[XCVG]

Because you still need to get that 5V, which means a regulator. You *could* replace the 7805 with a TI card or other switching regulator, but most people think it's not worth the cost.

 

[snowpenguin]

5v battery

 

[XCVG]

5v battery

No such thing. You can get 4.8V batteries, but only in NiXX flavour. Also, it will only be usable when at a certain range of charge levels. Consoles typically need power pretty close to 5V.

 

[samjc3]

5v battery

No such thing. You can get 4.8V batteries, but only in NiXX flavour. Also, it will only be usable when at a certain range of charge levels. Consoles typically need power pretty close to 5V.

as it just so happens, i have 4 5v 4500 mah li-po packs right here. each is comprised of 1 5v cell. i might be willing to sell them. they are brand new, but i have no charging circuits for them, unless you want it as a single pack. (they are from an energizer xp18000)

 

[βeta]

LiPos only come in 3.7v cells. Prove me wrong.

 

[samjc3]

LiPos only come in 3.7v cells. Prove me wrong.

ok. you are right. the are just mislabeled. i checked with mah, fluke, and they put out 3.92 volts, roughly. they are labeled specifically for the output after the crazy converter board.

 

[samjc3]

LiPos only come in 3.7v cells. Prove me wrong.

umm. yeah. you are right. they are mislabeled.

 

[βeta]

That almost sounds like sarcasm.

 

[samjc3]

That almost sounds like sarcasm.

worry not. it is true. they are written on in sharpie.

 

[βeta]

XD

 

[samjc3]

something about them screams "china"

 

[βeta]

I've got some untested 4Ah 7.4v LiPos that I wonder about......

 

[zeturi]

Some systems can be undervolted or overvolted if you bypass the 7805. My Genesis 3 operated on 6v after bypassing, as well as 4.5v. Could probably go lower.

Most people want to do 7.2v into a 7805 because almost everyone uses the PSone LCD, which needs that much voltage to run. If you are using DX screens though, no reason not to bypass the 7805.

And I will be using a TI card on my NES, since I've got eight of 'em.