Hero999
Banned
I made a mistake, meant the drain will be floating at 5 to 10V.MrNobody said: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",
Yes, you need to pull the source 10 or so V below the drain before it will switch fully on.do u mean the V(DS) would be 60V - 10V which is 50V..?
Yes, the poor MOSFET will have 50V between the drain and source whilst carying the current.Did i understand correctly..? If that is the case then the power loss would be too much...
Look at the graph of current vs gate source voltages on the datasheet.Can I ask, how to calculate the Voltage at source of MOSFET..? what formula should I use..?
Yes, a P-channel MOSFET is the reverse of an N-channel MOSFET, the current and voltages are all reversed.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)].
You don't, all it means is the gate needs to be -5V with relative to the source in order for it to turn on.The V[gs(th)] needed is -5V. How do I generate a negative voltage..?
No gate current flows in a MOSFET; the gate is an insulator.Is it negative voltage as in the current flowing from source to gate instead of gate to source (as in N-MOSFET)..?
The gate terminal needs to be 5V below the source (55V if the source is connected to +60V).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..?
The gate threashold is the voltage on the gate at which the channel starts passing current, it isn't a very accurately controlled parameter so a range between 3V and 5V is given. Don't be fooled into thinking it will pass any current up to the maximum rating once the gate is above the threashold voltage. Look at the graph on the datasheet to find out what gate voltage is required for a given current.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..?