Hi,
to control the temperature of a 400 W heater bed
Power is not that important. For Calculations you mainly need voltage and current.
--> and don´t post confusing informations:
Load is 12 V 250 W heater. So current of 21 A.
What now? 250W or 400W?
IRFZ48N...
I have never used a MOSFET driver before and I'm little confused about the circuit
If you buy a so called "logic level MOSEFT" then you may omit the MOSFET gate driver circuit.
In any case: You need to have
all the datasheets by hand and read through them.
If the datasheet doesn´t show "typical application schematics" then go to the IC manufacturer´s intenet site and look for related documents. Like application notes.
I don´t recommend to use random schematics from the internet, they often are not reliable and may contain mistakes. Use reliable ones from IC manufacturers, universities...
To your circuit:
Use example circuits form reliable documents and modify them for your needs. Always draw complete schematics. Hand drawn are OK.
Your schematic contains a lot of issues:
* missing power supply capacitors
* unconnected COM pin
* Check that no unused input is left floating (general rule: don´t let (unused) inputs floating, neither for digital circuits, nor for analog circuits)
* protect your MOSFET from overvoltage spikes with a zener. Especially with high speed switching you may expect high voltage peaks on drain-source due to stray inductance in wiring and/or load.
In the data sheet of IRFZ48, Gate threshold voltage is 2-4 V, that is the minimum volatge required to turn ON th channel,
No. This is not ON state. This is the edge where the MOSFET becomes conductive. See the tiny current of 250uA!
To know how much Gate current, I should check the output characteristics.
Static gate current is negligible with MOSFETS. Just care about V_GS.
I have a 12 V supply, so giving a Vgs of 12 V will create enough channel.
This is not the correct chart to look at. (mind the 20us pulse comment)
Look for the R_DS_ON vs _V_GS chart.
But in this case just the table value V_GS_ON (@10V V_GS = 14mOhms) is suffcient.
Calculate voltage drop and static power dissipation with the use of 14mOhms.
Klaus