Mosfet switch irf740 not working.

This is a 12v relay and your source voltage is also 12 v. You will never get 12v drop across the fet due to some channel resistance no matter how hard you drive it into saturation. Use a source voltage above 12v and it should work.

Also change the dimensions of the fet channel. You need to lower the channel resistance

Hi...but this circuit works. The youtube video is of it working. I am not sure how to make those adjustments...nothing correlates to any info on the datasheets. :-(

In the mosfet settings which you have made needs to be changed. Click on the mosfet settings and increase the width and reduce the length

But where do i get those settings. They are not on datasheets...I've searched and searched.

Replace the mosfet with a normal unaltered ec n mosfet, and put the switch on the negative side of the supply instead of on the positive side...it works fine then......you may want to drop the on-voltage down to 7.5v in the relay settings.

If you want the relay to stay latched on, then leave the switch on the positive supply side....but you will probably want to turn off the mosfet at some point to re-set it in that case.

Hi all...i guess i am really trying to understand why this circuit work in reality but not in thin this software??

Again...here it is working with the timer circuit. The timer outputs 11.5v ish and its a 12v relay.

A real live relay of 12v may activate at a lower voltage. The ec relay will only activate at the set voltage....you need to be a little adaptable in this respect. Also the mosfet parameters may be likewise less adaptable on ec.

Hi 2ctiby. The hard thing with the mosfets is the parameters here in the program are not on the datasheets. so I don't know how to set them.

Neither do I. It appears that many people here adjust those settings and so get things working...that is quite easy to do by trial and error, but if we were to buy a mosfet from a shop then we would not be able to alter it. I prefer to take a mosfet just as it is and work the rest of the circuit around it. I often notice also that people think their circuits are working properly with adjusted mosfets, but if you look at the bar on it you should aim for that bar to be completely open or closed as a switch...not half open which would be a power wastage.

Look for kn in data sheets. This is a constant value of A/v square. This constant is specific to each MOSFET.

You need to calculate it using the gfs i. e. Transconductance mentioned in data sheet and drain current.

Hi, applying a sufficient voltage to the MOSFET gate (VGS > Vth) will turn on the device via an electric field. The electric field is stored like a capacitor and therefore keeps the FET on unless the field is de-energised. Simply place a pull-down resistor (~50kR) from the FET gate to ground and the circuit works. Regarding MOSFET parameters, being new to EC I am unsure how to set a FET parameters similar to the datasheet. As you have said the adjustable parameters are not readily available information. As far as I can tell so far, you can increase the width to max clockwise and length to max anti-clockwise, the slowly adjust in reverse until behaviour is similar to datasheets values.