VVV
Advanced Member level 5
The driver I posted was just an example, for you to understand what they are and how they work. The P-channel MOSFET is your best option for the buck-boost.
But driving it may get a little tricky, since the PIC will be running at 5V and the source of the MOSFET will be at 7-10V. That means that even with the output of the PIC driven high, your MOSFET will still be turned on.
One way to prevent that is to have the power for the PIC regulated as a negative 5V with the "ground" connected to the + of your input. That way the PIC will drive the MOSFET with 5V. You do not want to drive the MOSFET with a voltage higher than 5V; see my post on the gate charge for the reason.
Nothing comes free, however, so this method would make the regulation part harder. But, since you are only chanrging a battery you can make the buck boost only produce a negative voltage equal to the difference between the battery charging voltage and the solar panel voltage and connect the + of the battery to the + of the solar panel and the - to the buck-boost output; basically the solar panel and the buck-boost are in series.
Added after 31 minutes:
To exemplify, here is a picture.
Notice how the MOSFET can be turned on in the first section.
Powering the PIC as I described gets rid of the problem.
Of course, you can always use an open-collector driver, but that means more parts and more power dissipated.
But driving it may get a little tricky, since the PIC will be running at 5V and the source of the MOSFET will be at 7-10V. That means that even with the output of the PIC driven high, your MOSFET will still be turned on.
One way to prevent that is to have the power for the PIC regulated as a negative 5V with the "ground" connected to the + of your input. That way the PIC will drive the MOSFET with 5V. You do not want to drive the MOSFET with a voltage higher than 5V; see my post on the gate charge for the reason.
Nothing comes free, however, so this method would make the regulation part harder. But, since you are only chanrging a battery you can make the buck boost only produce a negative voltage equal to the difference between the battery charging voltage and the solar panel voltage and connect the + of the battery to the + of the solar panel and the - to the buck-boost output; basically the solar panel and the buck-boost are in series.
Added after 31 minutes:
To exemplify, here is a picture.
Notice how the MOSFET can be turned on in the first section.
Powering the PIC as I described gets rid of the problem.
Of course, you can always use an open-collector driver, but that means more parts and more power dissipated.