Guide: Properly picking and using MOSFETs! 

Thanks, I have a few IRF1404's I picked up awhile ago because of it's specs. Couldn't think of anything wrong with it for this application. I usually use them for PWM applications.

@@rich1051414 IRFB7446 is even better than IRF1404 because it has lower ON resistance, lower input capacitance, and much faster switching, including much improved intrinsic "body diode" switching time.

@Billi Vandori , for actual current, yes. For "convention" current, it's probably right, but it sure is confusing.

Electron point of view: Source: provides electrons to the drain. Drain: receives the electrons. Source -> e -> Drain. Conventional current: Source

Can confirm, Russ is a geek :)

+Adrian Ciubotariu I'm a newbie but was also curious how this works. What I gathered (and take it as a grain of salt) is this: The 100 ohm resistor is to make sure that there isn't too much current flowing out of the output pin of the arduino. The gate basically works like a capacitor that is charged to switch the mosfet. So some current will flow into the game. The pins of the arduino are only rated for something like max 40mA so the 100 ohm limits that. Afaik the 10k is so the gate charge can dissipate again when turned off and the mosfet switches off correctly.

+Adrian Ciubotariu Gate resistors are very nice not only to prevent your driving source to get destroyed (a gate of a mosfet behaves basically a capacitor, so in the first instant your driver switches on, it looks like a short circuit to the drain!) it can, by limiting that initial burst of current, help to reduce electromagnetic interferences too. (in a simplyfied view: less harsh current impulse means less emissions and with that fewer possible problems). If you would go really deeper into all the interference topics, you would actually start to look at the electromagnetc impulses travelling along paths in your circuits inducing electrical currents in the conducters, but thats another topic for another day... Anyway, there is of course a trade of with increasing that resistor at the gate, especially once you have your heater PWM controlled, so it switches on and off all the time thousands of times per second. The gate resistor limiting the current flowing into the gate is now causing that capacitor to charge slower, so your FET stays into the transition between ON and OFF state longer. Now, thats where a FET really gets into trouble, because at that transition it has to dissipate a LOT of energy (the value of the drain-source resistor is changing from gigaohms down to milliohms, or the other way around.) A rule of thumb i use is to go with roughly 33 Ohms for gate resistors, but as usual, a rule of thumb is just that, and can be just as wrong as it can be right, depending on what you are doing and who is involved. (gate impdances and capacitance, conductor impedances and losses, driver output impedances...)

thanks to all for the reply, I received way more than I initially asked, but that's the + to the community, not just people printing, with general knowledge, but people with good understanding of all elements involved. reading all of this I realised I studied it, back in the day, but not enough, it seems. how it just went away, no idea... there were a lot of "duh, dummy!" moments :) Thanks to Dejay Rezme ExtraBase and, of course, *****

SuperCozMick hi sir this heated bead mosfet irlb8743.did u make one...i tryd buymt it keeps heating and shorting out the mosfet pls help with a diagram thank u

Switching speed depends on the gate drive. Down around 10ns for a power device using 'reasonably strong' gate drive. That means a specialized MOSFET gate drive circuit or chip, and you need to account for losses during switching (MOSFET isn't fully on, so you get high VDS and high RDS when the MOSFET is transitioning from on to off and vice-versa), etc. You will want an oscilloscope and probably an adjustable bench power supply while developing such a circuit, to help figure out what's going on.

sorry my bad the TC4420's won't work with 24V.

Svd1404t

Pawel WozniaK...relative of Steven :-))

Does the internal diode not handle this Siana ? 😕

HI , can i use a 10v vgs mosfit to be driven from the ramps stock mosfit ?

I really doubt that the IRL540NPBF has a maximum Rds of 53mΩ at 5V Vgs. The Vishay datasheet that I have (Document Number: 91021, S11-0510-Rev. B, 21-Mar-11) shows a maximum Rds of 77mΩ at 10V Vgs, and it doesn't seem possible to have a smaller Rds with a lower drive voltage. What is the datasheet you are drawing your information from?

Bruno M. , Old post but in general ignore the front page marketing bs and head for the graphs and other detail info on the data sheet. You'd need some beefy drive circuit to deal with the gate capacitance and proper board layout to pull off a short 200amp pulse.

This is false. On an n-channel mosfet, gate must usually be around 10 volts higher than source to switch on. On low-side configurations it's fine to just drive it at vcc. In high side, you need a way to step the voltage above whatever will be coming out of source. Bootstrapping IC's or a bootstrap capacitor can be used for this

Gate to Source voltage is what turns the MOSFET on or off. It starts to turn on at the "threshold voltage". If you hook Drain to the Gate, that's a specialized circuit used in some circumstances (too long to write here). Whatever the Drain to Source voltage is doesn't affect whether the MOSFET is on or off; it interacts with how 'on' the MOSFET is to determine drain current.