How to choose a mosfet

Hi everybody,

I am not very strong in electronics but I try to be autonomous.
My problem is this: how to choose the right mosfet?

I would like to drive a 20-watt 12-volt heater. How to choose ? what should i search in the datasheet?

I prefer an explanation, a link to a tutorial rather than an immediate answer that says: take the mosfet IRFxxx

Thank's for your help

Nicolas

Hello,

For pulsing in your case use a N-Chanel mosfet look for a mosfet with +/- 120 - 200 watts the higher the better and the lower RDS(on) the better!

The lower the rds(on) the less heat the mosfet will produce. (the less resistance the mosfet has for to open) The most mosfets needs about 2 Amps to open fully. Pulse the mosfet with the 12v you have.

Fets to choose on: Hexfet, Hyperfet etc all with low rds(on) types are fine to use!

Greets,

Nena

20W @12V is a current of ~1.67 amp load current (quite low).

What will be driving the MOS FET?

NenaGirl:
The most mosfets needs about 2 Amps to open fully.

Please explain.
Leo..

Wawa:
Please explain.
Leo..

Lets say if you have an mos app. You need to pulse a signal over an atenna. The antenna is 200v and 20 Amps and you are only using a arduino as driver without external powering the mosfet. So you drive the mosfet with 5 volt.

You will see that the mosfet does NOT fully open and you wont get the ful 200v and 20 Amps on your antenna, also your puls is not that what it should be.

When you manage to get almost full power to the mosfet gate the mos can take the nessesary amps to open fully and you can supply the antenna with the full 200v 20A.

To solve this problem they invented the Mosfet DRIVER for this problem.

Greets

Nena

Nico84:
take the mosfet IRFxxx

In an Arduino world I'd be looking at IRLxxx not IRF. You didn't say yet, but can we assume the gate is on an Arduino data pin, seeing as you asked in an Arduino forum? If so you want a logic level fet like IRLZ44N which is overkill but cheap enough, 55V, 47A and 25mOhm RDSon @ 5V.

Nico84:
Hi everybody,

I am not very strong in electronics but I try to be autonomous.
My problem is this: how to choose the right mosfet?

I would like to drive a 20-watt 12-volt heater. How to choose ? what should i search in the datasheet?

I prefer an explanation, a link to a tutorial rather than an immediate answer that says: take the mosfet IRFxxx

Thank’s for your help

Nicolas

Your heater needs 20/12 = 1.7A approx. You choose a MOSFET that won’t need a heatsink by requiring the
total dissipation is 100mW or less, which means I-squared-R < 0.1, so R < 0.1/I^2, ie R < 0.036 ohms.

So choose a logic level device, Rds(on) < 36 milliohms, Vds can be 20V or more, 30V is a reasonable value
(higher voltage devices tend to have much higher on-resistance).

Actually you can get away with 200mW dissipation, but it will then be very hot and this is avoidable, devices
of 30 milliohms or less are commonplace today.

NenaGirl:
Lets say if you have an mos app. You need to pulse a signal over an atenna. The antenna is 200v and 20 Amps and you are only using a arduino as driver without external powering the mosfet. So you drive the mosfet with 5 volt.

You will see that the mosfet does NOT fully open and you wont get the ful 200v and 20 Amps on your antenna, also your puls is not that what it should be.

When you manage to get almost full power to the mosfet gate the mos can take the nessesary amps to open fully and you can supply the antenna with the full 200v 20A.

To solve this problem they invented the Mosfet DRIVER for this problem.

What has an antenna and all the rest got to do with anything. You could have just mentioned gate charge.
We all know that you have to use a mosfet driver when PWMing at high frequency and/or high drain currents to keep switching losses down.
But this all is irrelevant when switching a <2Amp load on/off.
The 20mA that an Arduino pin can deliver comfortly is more than enough for that.

What is important is to use a logic level mosfet,
so the mosfet is almost fully ‘on’ with the 5volt an Arduino pin provides.
Leo…