GBA Li Po battery mod - help needed!

Hi all

I'm a bit of a noob when it comes to designing my own circuits and whatnot, but could anyone tell me how I can wire up a LiPo battery to the GBA, with a micro USB charger? For instance is it as simple as wiring a USB charger module to the battery, and then wiring the battery in parallel to the GBA?

Cheers

 

Yes assuming the GBA can take 4.2v max. You will need to design a shutdown circuit as well.

 

I was looking at this http://hackaday.com/2015/01/01/game-boy-with-lithium-batteries-and-usb/, and although that is a GBC rather than a GBA, I figured the principle would be the same. This guy has wired the output from the charging module to the battery contacts of the game boy, and then run a wire from the battery contact to the battery. Presumably, this would allow the unit to be used and charged at the same time. I managed to find a charging module that has two outputs, one is the battery out, and the other is a direct passthrough from the 5V feed, I'm thinking I could wire the battery up and connect the passthrough directly to the GBA via a diode to drop the voltage to more in the 3V range.

 

You don't need a charging circuit with two outputs. You just need to make sure the battery negative sense is isolated with the Rsense from the system. So the charger can do the voltage difference and determine when to stop charging.

I'm designing the game gear around this charger: http://www.ti.com/lit/ds/symlink/bq24100.pdf

Go to page 30, they have a good diagram of charger with a system load.
If you ground out the TTC pin when the device is turned on, this will disable the internal safety shutdown timer. Which will keep the pack fully charged and power the system with the battery charger. Once you turn off the device. The safety timer will engage and the charging will shutdown once the the safety timer is reached or detection from the voltage drop.

 

The nominal voltage of a lithium cell is 3.7V, so using a diode with a drop of 0.7V would indeed bring the voltage down to a safe level. However, their charging and maximum voltage is 4.2V. With a single diode, the voltage would be at 3.5V which I feel is a bit high. You might be better off using two diodes in series, which would bring the voltage down to the range of NiMH rechargeable batteries, which can be used in Game Boy's just fine.

I've never used those small lithium charger boards, but I feel like there's a chance the output might be regulated at 5V so you'd have to measure it before using it. If you compare the PCB with that of the output-less version, there are additional ICs and only the negative terminal is connected directly to the source.

What the guy did in the Hackaday post was simply plug the battery and charger in parallel to the battery contacts, with a diode in series on the positive terminal for both. You should be able to do the same with the newer lithium charger boards, in case the output is regulated to 5V. Alternatively, you could also use 3 diodes in series to drop 5V to 2.9V.

Btw, since the link to the original blog post is broken, here's an archived version: https://web.archive.org/web/2015010...kispaces.com/Repair+-+Gameboy+battery+upgrade . Sadly, all the pictures and schematics are lost.

Designing your own circuit around a charging chip is indeed a better solution, but I think Xaranar is looking for something more "off the shelf".

 

I just want to use a rechargeable LiPo battery in a standard GBA, and for me to be able to "play and charge" at the same time, so to speak, and I'm just wondering about how to do that.

Figured it out. I've wired it up so that the battery has a diode in series to the positive battery terminal, and I've wired the 5V line directly to the positive battery terminal also, using two diodes in series to drop the voltage. Then I used a PNP transistor with the 5V line on the base leg, so when a current from the USB is flowing, the transistor is off and stops the current from the battery powering the unit, as well as charging the battery.

 

Can you pull the power out without interrupting play? Like will it switch between charging and battery without the voltage dipping low enough to power off?

 

Yes, I can. I actually had to wire two batteries in series to get it to function correctly, as the emitter of a PNP transistor requires a constant, relatively high voltage, and with just a single battery I couldn't get a high enough voltage in the circuit to power the unit reliably, even with the base pin at 0V.