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Topic: Choosing the right mosfet (Read 818 times) previous topic - next topic

Scottwhite88

Hi everyone,
I've been looking loads into MOSFETs for a project I want to get on with. My problem is there are sooo many to choose from. I know the rough basics of what to look for low Res(on) etc.

I would like to use the IRL6372TRPBF dual mosfet. I want to make a shield for the Arduino mega. which is capable of controlling a 12v water pump running at 4 amps max and 1 x 12v solenoid valves running at 4.5amp max current draw.

Now to me 8amps going through that tiny chip seems a lot. Is this also 8 amps per fet or 4 amps per fet?

Basic circuit layout is 5v with resistor connected to mosfets gate. Then drain connected to solenoid with a diode in parallel. Then source connected to ground.

I want to be able to use a MOSFET without a heat sink ideally.

Am I completely mad or will this work. I've just looked at so many graphs and data sheets now I think I'm just ending up confusing myself.

Thanks for any help

FredScuttle

#1
Jul 17, 2018, 11:31 pm Last Edit: Jul 17, 2018, 11:38 pm by FredScuttle
1 solenoid valve draws 4.5 Amps?
The datasheet claims an Rds of 18 mOhms MAX, so 4 Amps squared times 0.018 = 0.288 Watts per MOSFET, maybe won't need a heat sink?
Awww! Who needs an instruction manual to use a simple chain sa......

MorganS

Junction-to-ambient is 62ºC/W "when mounted to 1" square copper board."

0.5W (both MOSFETS driven) gives 31ºC rise above ambient temperature. Maximum junction temperature is 150ºC. Even if you use less copper on the PCB, you aren't coming close to overheating it. It will get hot - maybe too hot to touch - but it should handle that power just fine.
"The problem is in the code you didn't post."

MarkT

First point - is 4A the stall current rating for the motor?  That's the maximum you need to use for specifying
the MOSFETs, not the max continous current.  Stall currents can be much higher than running currents.

If PWM is being considered (ie motor control)  careful attention to switching losses is needed as they
can dominate the heat dissipation if switching is sluggish and PWM frequency is high.

Switching 8A will mean lots of decoupling will be needed in your supply, and good layout practice to avoid
radiating lots of noise out - avoid big loops, route each connection alongside its own ground return or use
a groundplane on the PCB.

Personally I'd choose at least 40V MOSFET, with high current switching of 12V I'd immediately assume 24V
transients will happen at turn-off due to stray inductance and would like to have a little more headroom.

Adding a ~18V TVS diode across the 12V on the board across the FETs might be a wise precaution to circumvent
the problem.
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