7.2v into 7808

ShockSlayer · Post by **ShockSlayer** » Thu Apr 05, 2007 3:23 pm

If I put 7.2 through a 7808, would it change or still be 7.2

I'm putting in a 7808 as a saftey measure to adapt 12v from a n64 wall adapter to go down to 8 for a psone screen.

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timmeh87 · Post by **timmeh87** » Thu Apr 05, 2007 3:32 pm

nothing would come out, the regulator will be in cutoff.

Kurt_ · Post by **Kurt_** » Thu Apr 05, 2007 3:35 pm

You can have a switch (or a fancy plug for your wall adapter that shuts off a connection when you plug it in) that changes from battery power to wall => regulated power.

ShockSlayer · Post by **ShockSlayer** » Thu Apr 05, 2007 3:41 pm

A switch....

GOD IM AN IDIOT SOMETIMES!

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codeman · Post by **codeman** » Fri Apr 06, 2007 10:55 am

Ok...I haven't been able to test this circuit yet, but I've only seen people say "put in a switch" to change from battery to wall power...so I took a few minutes to think of a different way to do it.
Yes, you could use two diodes but lots of people complain about the diode dropping too much voltage and so the battery life is cut. This circuit fixes that. If someone wants to test it...I'm confident it will work, but it's untested as of yet.

The "AC" source is the wall plug. It's not normally there, so it's normally an open circuit. When it's plugged in, the diode is forward biased, putting ~11.3 volts into the regulator, and the PMOS MOSFET is turned off, blocking the battery current so you can then simply remove the battery with no problems

Post by **Skyone** » Fri Apr 06, 2007 2:37 pm

Much better, I think people need to learn how to utilize diodes better (including myself)

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timmeh87 · Post by **timmeh87** » Fri Apr 06, 2007 3:54 pm

and MOSFETs

Post by **gannon** » Fri Apr 06, 2007 4:18 pm

BOBAFETTs are the best

Really though, it's been over a year since I've done semi-complex electronics involving transistors/diodes etc, barely remember anything -_-

Website · Post by **Life of Brian** » Sat Apr 07, 2007 8:30 am

Is there any way you could post a larger picture of that schematic? I'd like to try it out. If it works, man that would be one snazzy feature. I'd look like I actually know what I'm doing

I'm about halfway done with my next SNESp and plan on powering it with li-ion batteries with the option of running it off of wall power, so that would be pretty sweet to have.

Kurt_ · Post by **Kurt_** » Sat Apr 07, 2007 10:02 am

Why is everyone overlooking the simplest option?

Use the charger as your wall power!

ShockSlayer · Post by **ShockSlayer** » Sat Apr 07, 2007 10:09 am

Kurt_ wrote:Why is everyone overlooking the simplest option?

Use the charger as your wall power!

The charger sucks!

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codeman · Post by **codeman** » Sat Apr 07, 2007 11:53 am

Here's a bigger version:

And as for using the charger as wall power...I don't even plan on having an internal charger. I'll have removable batteries, so when I finally make a portable I want to be able to switch to wall power and remove my batteries without interrupting game play

Kurt_ · Post by **Kurt_** » Sat Apr 07, 2007 12:53 pm

With my Lithium Batteries the charger plugs into them and you can have uninterrupted game play without removing them...