I've the following schematic for a buck converter charger circuit.
This is getting power from a 10Watt Solar Panel and charges a 7AH 12V Sealed Lead Acid battery.
I'm controlling the BC817 with PWM from an ATMega2560 at 62.5 Khz and usually the current is around 500 mAmp.
My issue is that the IRF4905 gets extremely hot during charging. With a small aluminum heat sink attached, it does reach temperatures near to 90 degrees Celsius, which is concerning.
The IRF4905 mosfet is designed to handle current up to 74A, so I really don't understand why this is happening here.
Any ideas are welcome.