7805 8v Power Board rev. 1 Complete and Sucessful!

Post by **bicostp** » Sun Aug 07, 2005 2:11 pm

If any of you have read my thread in the PSX/32-bit section of the forum, you'd know that I have had a lot of trouble figuring out a way to get 8 volts from my 12 volt Laptop battery. Well now my problems are over. I built a circuit board that boosts the output of the 7805 to 8 volts using resistors and a switch.

Here's the schematic I threw together this morning.

I have sucessfully built and tested this. It puts out 8.1 volts on the regulated pin, and whatever you put into it comes out the unregulated pin.

All the parts (I assume) and be purchaced at RadioShack. (If it's asked for I'll make a parts list.)

If you want (and if I can find the camera ) I'll post pics of my board.

This could definitely be modified by replacing the resistors with 1k potentiometers, but it's Sunday and the plaza RadioShack is in is living hell on the weekends, so I just experimented with resistors until I got about 8 volts.

)

I hope this helps anyone without an easy source of 7808s.

(edit: I know it may not seem like much, but it's the last thing I need for my PSonep.)

Post by **Triton** » Sun Aug 07, 2005 2:27 pm

yeah, thats cool bico! kinda pointless if you can get 7808s but useful if you cant!

Post by **bicostp** » Sun Aug 07, 2005 2:31 pm

Well my only other option would have been to tear apart a $20 7.5v car DC converter...

Seriously I couldn't find 7808s ANYWHERE!!!

And my folks didn't want me to buy/trade over the internet, so I went and built this out of scrap parts from a box in my closet.

I'm very frugal. Can you tell?

*runs off to cut out coupons and fill rebate offers

Post by **SpongeBuell** » Sun Aug 07, 2005 2:48 pm

wouldn't the resistor values change based on amperage used?

Post by **bicostp** » Sun Aug 07, 2005 2:56 pm

Well, all the websites I found had roughly the same values for 8 volts. Most of the difference in values changed the end voltage.

I first hooked up my 4500mah laptop battery (The one I plan on using), and the end voltage was 8.10v. I hooked up my 1800mah RC battery (the one I was going to use), and it was at 7.95v. So yeah there's a bit of difference, but I didn't really test a lot with it. (And of course if the 200 resistor was replaced with a 1k pot you could tweak the voltage to exactly what you need, but like I said I'm not dealing with the stores today.

)

So the PSone can safely run off of 8 volts, right? I'm 99% sure it can...

Post by **SpongeBuell** » Sun Aug 07, 2005 3:15 pm

yeah, a PSOne should be able to do that. And the battery doesn't matter, it's the load that you are using. For example, an LED doesn't draw as much as an xbox. Ohms law says that E=IR, or voltage is current times resistence. because the resistors are the same, R is the same. Now, if the current draw goes up, so must the voltage to keep up with it.