Transistor vs MOSFET
Thanks mneary!!! Great stuff - just what I needed. I had hoped to use alkaline batteries but the enclosure I am using does not allow for servicing of the batteries so I had to go with a recharging arrangement.
I originally had a MOSFET but I switched to a transistor because I thought that a MOSFET would cause a problem with the batteries. My limited understanding of MOSFETs is that they bidirectional and will pass current both ways when turned on??? If true, then whenever the unit is powered from the AC/DC supply, the MOSFET would pass current back to the NiMH cells. I would have no way to stop the current when the batteries were fully charged and this would eventually cause the batteries to overheat, vent and go bad. I was hoping that the transistor would block this inadvertent overcharging of the cells.
I did not show the entire diagram for simplicity sake and since I was fairly confident that I had the rest of the circuit designed properly. I have attached the entire power supply circuit. Does this all seem ok or am I still off base. Thanks.