Powering 7805 regulator consols with 5v

(newbie on mods, old gamer.)

Hi, I was thinking, as a lot of consoles are regulated by a 7805, is it possible to power them with the correct current but feeding a 5v tension? Would it be necessary to remove the regulator or can I just use 5 v and it will pass through it?
Thanks!

 

As long as the console only uses the regulated 5V then sure, you can bypass it by removing the 7805 and supply 5V directly on its output.
But this requires that everything in the console is powered from that 5V, if there's anything else using power from any place other than the 7805 output it won't work.

 

Are you trying to use a switching 5v power source?

 

Just trying to keep the tension low for heating purposes. Besides, using usb to power the systems would be nice as well.

 

This is also something i've wondered in the past. Removing the 7805, and just powering the console directly with 5v

 

Yep you can, I have powered an nes off of 5 volts. There are some factors to consider,
if the psu contains switching regulators there could be artifacting in the video. I think it was Bad Ad that brought this fact up, then again most psu's have components to filter noise. Rule of thumb is to base the amps of the psu you need with amps provided by the original 7805. I know there is a 7805 variant out there that can provide 1.5 amps.

 

And do I really need to remove the 7805? can I just use the out leg of it for tests?

 

If I'm not mistaken most of the newer clones use a 5V ac adapter directly. I'd say you just need to make sure it has good amperage to give enough juice and a a good quality adapter helps too.

 

Good to know! But, when power hits the 7805, 5v 1A, directly from the adapter, it will be 'regulated' again causing loss or noise? That's my concern... how would the regulator act in this case, in which he is not needed but used.

 

Typical 7805 require at least 7v to work properly, under that value the behaviour is not clear/undefined, it would require testing to be sure.. Really, you should bypass it if you want to use 5v directly.

 

The parameter of interest is dropout voltage.
Supplying directly on the 7805 output is possible and will work, but those devices aren't design to withstand reverse-current, so the 7805 may die in the process. But if you're looking to bypass it anyway...

 

Also do NOT use a 5V AC adapter directly to the 7805 output pin! Only DC, you will mess up your console otherwise.

No, the regulator is bypassed.
But if your concern is heat/electricity economy, I would just swap the linear regulator for a switching DC/DC converter instead.

 

you could just get a modern 7805 that produces almost no heat.

http://www.ebay.com/itm/PSU2-3-3-17...324080?hash=item3ad8ea1ab0:g:7VYAAOSwd4tUCN4b

 

So, if it's bypassed, there's no need to modify the system at all.

I've read in another thread that this regulator, somehow, generates some noise and/or artifacts...

 

Depends on the quality of the one you buy. if its a cheap chinese one then you'd get those results.

 

guess if I have to subsitute, I'll go on this one <-
But the perfect solution would be the bypassing situation.

 

Almost all 5V supplies have a lot of noise on their output. If you're going to use that in your consoles, you have to beef up the smoothing capacitors. Remember that one of the reasons they used 7805 was for their excellent ripple rejection and very fast load management. Also they guarantee 5V +- a few %, whereas a regular PSU has higher tolerances.
At least check the actual voltage under load (when the mod is done).

If the only goal is less heat produced, then it will be better to use a ~9V DC PSU into the 7805. This way you'll often have about 8.5V into the 7805, so it only drops 3.5V.

 

Be very careful with the 5v adapter. Many AC-DC adapters are a couple of volts higher than what is stated when not under load, and are expected to be pulled down by the load. You won't know how much or at all without testing this, so you might accidentally inject 7 or 8v into a circuit that is not designed for it.

 

I did this to my AV Fami, SuFami, and Genesis. It works fairly well, just remove 7805, connect I to O, and you should be good to go. There was some voltage sagging on my Genesis so I adding some bodge wires to go from the 7805 pads to a couple other spots on the board with a beefy capacitor.

Biggest benefits are that you don't need the giant AC wallwarts any more and the systems produce no heat. You can just power with a simple USB power supply, easiest way is to re-terminate the power cords with USB.

This is definitely true though:

I found that a LOT of 5V power supplies are crap. Actually for me unless I use a Sony or Apple brand USB AC adapter or a direct line from a PC USB port you'll end up with messed up voltage input. I'm not sure what Apple is doing differently but the 5V output of their USB adapters is pristine.

And make sure you don't have a fake cause those are actually pretty dangerous. On my SNES I even got a ton of noise with non-Apple/Sony AC adapters.

This is also a very good idea if your main goal is to just have no heat:

I've been doing this on every system I've bought with a 7805 in the last couple years instead. I think it's also safer since you don't have to worry about someone in the future frying your systems by plugging in a 12V power input direct to 5V parts.