Hero999 said:
Because N MOSFETs require the gate to be at a higher potential than the source. With your circuit the gate will be at 15V, therefore the source will flowat at about 5V to 10V giving a massive voltage drop across it and only a small voltage to the motor.
A P MOSFET will turn on when the gete potential is below the source, so if your motor requires 60V and P high side MOSFETs are used they will need 45V to 50V when on and 60V when off.
Thanks for your explanation.. Initially, i do not really understand.. but after searching on the internet, i found MOSFET application note by DALLAS semiconductor.. Now I understand..
When you say "source flowing at about 5 to 10V", do u mean the V(DS) would be 60V - 10V which is 50V..? Did i understand correctly..? If that is the case then the power loss would be too much...
Can I ask, how to calculate the Voltage at source of MOSFET..? what formula should I use..?
If I use P-MOSFET for high-side driver, the source terminal (of MOSFET) would be connected to the 60V and the drain would be connected to the motor rite..? So, the current would flow in reverse (from source to drain) rite..?
I searched the internet and I found P-MOSFET for the circuit..
The datasheet can be obtained from here..
https://www.farnell.com/datasheets/44775.pdf
From the datasheet, there are 3 things i need clarification..
The first one is V[gs(th)]. The V[gs(th)] needed is -5V. How do I generate a negative voltage..? Is it negative voltage as in the current flowing from source to gate instead of gate to source (as in N-MOSFET)..? So, to solve that, I need to connect the source terminal (of MOSFET) to +ve of 5V supply and the gate terminal (of MOSFET) to -ve of the same 5V supply..?
Second thing is, the minimum V[gs(th)] is -3V, maximum V[gs(th)] is -5V and the V(GSS) is +/- 30V. How do I interpret these data..? Does it means that my gate voltage cannot exceed -5V..? How about the VGSS..?
Yeah.. i posted alot of questiong.... After searching the internet for days, i understand abit of MOSFET but there are still gaps, questions that i still cannot find answer to, things that are still gray and uncertain to me... Thanks for your time and your patience...