Hello, I am thinking of building a small Arduino MPPT solar charge controller capable of around 20 watts. I have a few questions. One; Would a P channel MOSFET be suitable for the switching or would I have to use a N Channel with High side driver chip (If so, any suggestions on a chip?). Two; Would I be able to use a simple buck conerter circuit like this one from wikipedia? Buck Circuit Diagram
Thanks in advanced
Nathan XD
Hi Nathan,
Assuming that your N-channel FET driver is going to be powered from a battery connected to the output of the buck converter, the problem is that the switching signal has to be amplified to a voltage which exceeds the battery voltage.
One solution is for your switching signal to drive a transformer where the secondary winding is connected to the gate and drain of your FET. The circuit between the secondary winding and the FET may have to be modified depending on your switching frequency.
Tell us more.
Is the result perhaps a steady 5V, or do you want to charge Li-ion batteries or lead (gel)-batteries ?
There are many good DC-DC converters, Solar power converters, battery chargers and so on. Most Li-ion battery chargers have chips that protect the batteries. You can't get that quality level with an Arduino as the switching unit.
However, the Arduino can be used for a switching regulated voltage, but only in some special cases. For example to generate a regulated high voltage for a Geiger counter.
Have a look at this: USB / DC / Solar Lithium Ion/Polymer charger [Rev C] : ID 390 : $17.50 : Adafruit Industries, Unique & fun DIY electronics and kits
Don't miss Tim Nolan's MPPT design. It answers most of your questions, and you should also take note of his back-to-back mosfet arrangement so you don't need to include an inefficient diode to prevent power draining from the battery when no sun is present.
Thanks for the advice! I will be using this circuit to charge a 12v SLA battery. Would it be possible to use a boot strap circuit to drive the MOSFET in the high side?
Yes, I think the bootstrap circuit would work fine with a buck converter. I'd suggest using an optocoupler to connect the bootstrap capacitor to the gate. Also it might be worthwhile using a second optocoupler to discharge the gate in order than the FET switches off as quickly as possible.
So would a circuit this be OK? Practical MOSFET Tutorial #6 - DCOI Opto-Isolator Driver - YouTube
Or circuit similar to the above?
Thanks in advance