Hello,
I'm trying to build a high current MSFET switch to control the temperature of a 400 W heater bed. Instead of bying a board, i thought I would make one. I got following components from nearest store,

IRFZ48N and IRFZ48N MOSFET driver.
I have never used a MOSFET driver before and I'm little confused about the circuit

Following is the schematics of the circuit that I made. I haven't actually made the circuit in board since I don't know whether circuit is correct or not.




I have some general doubt about understanding the MOSFET data sheet. Load is 12 V 250 W heater. So current of 21 A.
In the data sheet of IRFZ48, Gate threshold voltage is 2-4 V, that is the minimum volatge required to turn ON th channel, but it doesn't have enough channel width for 20 A, so I have to choose a gate voltage that is enough to create a channel for 20 A it should be less than maximum allowed Gate voltage, which 20 V from data sheet.



To know how much Gate current, I should check the output characteristics.



I have a 12 V supply, so giving a Vgs of 12 V will create enough channel.

Am I right up to this point? Is there any other general things that should consider for MOSFET switches??

Thanks

 

hi A,
Initially you say 400 Watt heater load then you say 250 Watt, which is it.?

A 12V Gate to Source voltage will switch the MOSFET hard On.

One extra point is the heat generated by the MOSFET, at 400W, 33Amps I make it approx 20 Watts, so a large heat sink will be required.

How are you powering the 12Vdc, 33Amp source.?
E

 

This might help -

https://www.designworldonline.com/how-to-select-a-suitable-heat-sink/

https://www.rohm.com/electronics-basics/transistors/calculating-transistor-temperature


Regards, Dana.

 

Sorry for the late reply. Since I wasn't getting a reply to the question, I posted it on another forum, where I got some suggestion, and I forgot that I even made a post here.

It's 250 W heater. I am also planning to use a 400 W heat bed too, but it's 24 V. Sorry for the confusion.


This is the circuit that I made and it worked, I tested it using a 40 W heater.

Then people in other forum suggested to put capacitors in power supply, adding Zener voltage protection to gate and avoid floating pins.

So I made following changes to circuit,



Is 12 V zener enough ?

To avoid floating of unused pins, what should be used, pull down or pull up??


"A 12V Gate to Source voltage will switch the MOSFET hard On."

Is that a problem ? According to datasheet I can give 20V max as Vgs.

As per the data sheet a 10V Vgs gives Drain current of 33 A with Rds = 14 milli ohm
I had a 12 V supply, so I thought about using it.

How can I know the Vgs voltage required to create a sufficient conductive channel for a given current? What graph or parameters to look for in datasheet??

From where I sourced the chip, salesman warned me about the heating of MOSFET. I bought a large heat sink and thermal compound. I could cool it with a fan if needed.

Like I said I want to control a 24 V, 400 W heater with circuit too. Is it okay If use a 7812 to regulate voltage to 12 V and use it power the Gate Driver chip, so that I don't have to use a separate power supply for load and driver ??

Thanks