Interchanging between Wall and Battery Power

codeman · Post by **codeman** » Thu Mar 30, 2006 8:53 pm

anotherperson wrote:The issue with that is that I would have to have a switch to disconnect the battery back from the N64 and screen

Nope, that's the beauty of using the diodes. I'm guessing you're not understanding what goes on with the diodes, so here goes. The only important thing to have (though i guess it's not instant death if this isnt the case) is a wall supply with a higher voltage than that of the battery. Assuming you're using schottky diodes, you'll have about a 0.4v drop across each diode. When the battery is connected, say at 7.4v, the input voltage to the DC-DC converter will be 7v. When the wall plug is put in, say at 8.4v, the 0.4v drop across its diode will put the input of the DC-DC converter at 8v. It's not possible to have the same node at a different potential than itself...so one of the diodes "turns off", conveniently the one that's connected to the battery.

When the wall plug is put in, the battery diode is reverse biased and allows the battery to source no current at all. Once the battery is not sourcing current, it's like holding a AA in your hand, it does nothing. You can take the battery off and nothing will happen, or you can put in a charging circuit or whatever.

The diodes on the charger chip are just because i'm paranoid. If there was a sudden surge in current because the N64 had to draw an insane amount of polygons or something, the voltage feeding the input to the charger would drop for an instant, and I'm just not sure how the chip would react to that. The diode prevents anything bad from happening.

And they rode off into the sunset
The end

XFactor · Post by **XFactor** » Thu Mar 30, 2006 9:59 pm

I'm probably just going to stick with a circuit without diodes since the batteries can be charged and undergo a load at the same time. The only thing that concerns me is the chip's reponse to either plugging in the wall adapter during play or disconnecting it during play.

However, i am still considering using diodes if i use the following method: I have my battery and my wall charger. I split the lines of the battery back so i have two postives and two grounds; one pair goes to the N64 through diodes and the other goes to the outside of the case as a charging point. The wall charger would have its own set of lines coming from the exterior of the case, joining with the N64 battery line after the diode. In this configuration, i could play using wall power without the concern of shorting the system.

Codeman, are the diodes that "turn off" only shottky diodes? I bought some 3A diodes from Radioshack and i don't know if they do exactly what you just clarified for anotherperson.

codeman · Post by **codeman** » Fri Mar 31, 2006 9:48 am

anotherperson wrote:I do understand how diodes function. I forgot to mention that I didn't want to use them because of the voltage drop.

Oh, ok...well maybe my endless typing will help someone else. Why is using a relay not a good idea to switch between? Wouldn't that be better/easier than having a physical switch?

XFactor: The only reason I mentioned schottky diodes is because they have a lower voltage drop than a regular silicon one. The operation is the same, but the battery life will be better with a schottky. So yes, your diodes will do the same thing

XFactor · Post by **XFactor** » Fri Mar 31, 2006 2:10 pm

The radioshack ones i bought say they are made out of epoxy. is this a bad diode?

codeman · Post by **codeman** » Fri Mar 31, 2006 9:37 pm

Well, if you think about it, your inductor and output capacitor are already storing energy for you. If you could get a relay with a switching speed somewhat on the order of the swtiching speed of the regulator i think it would work fine. It shouldn't be a big problem if the inductor isnt charged for a few cycles, it should react fast enough to recover...maybe. Try it out, just make sure you pause the game or something before plugging it in so it's not drawing a lot of current.