IRFZ48 N and FAN7392 MOSFET Switch

1. IRFZ48 N and FAN7392 MOSFET Switch

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

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2. Re: IRFZ48 N and FAN7392 MOSFET Switch

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...

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

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3. Re: IRFZ48 N and FAN7392 MOSFET Switch

There were mistakes I made in post, load is a 250 W. I had a 400 W , 24 V heat bed besides me when I was writing this post, sorry above that.

To know how much Gate current, I should check the output characteristics.
Static gate current is negligible with MOSFETS. Just care about V_GS.
what I meant was gate voltage.

This is not the correct chart to look at. (mind the 20us pulse comment)
Look for the R_DS_ON vs _V_GS chart.
I couldn't find any Rds ON vs Vgs chat in the data sheet,
but in the electrical characteristics table

RDS(on) Static Drain-to-Source On-Resistance ––– ––– 14 mΩ VGS = 10V, ID = 32A

That mean 10 Vgs will be enough for 32 A, right?

voltage drop = 0.014 * 32 = 0.448 V
and power dissipation = 32*32*0.014 = 1.334 W
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...
This schematics is drawn by me, I couldn't find any thing online, I have drawn this based on the example circuit found in the datasheet.

When I made the circuit on PCB, I connected COM to ground and when tested with LED as load, it's working

And to solve some issues that you have mentioned

Would this be fine?
I think I can pull down the SD and HIN to ground using 10 K pull down resistor though not sure about HO< VB and VS pins.
Datasheet mentions about bootstrap resistor and diodes, what are those?

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4. Re: IRFZ48 N and FAN7392 MOSFET Switch

Originally Posted by Athul
bootstrap resistor and diodes, what are those?
The Internet, and expecting other people to do incredibly basic research oneself should do - what are those? ;)

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