MOSFET Bidirectionality

You mean drain and source. Not gate and source. Right9

Application is e. g., If you have an old laptop battery, you can find drain to drain or source to srouce mosfet configuration at battery management. So even if charging or draw current thoses switches are used to protect against over charge or undercharge or over current in both direction. The body diode avoids that you can do that with just one mosfet.

Most real life Mosfets have a body diode. ... and that can be used to advantage in certain circumstances. That diode construction happens as a consequence in the design rather than as an added extra feature. The E. C. Mosfet is not lumbered with having to implement such a non- purposeful feature, but this means that we should stick to arranging them in the proper way and not try to use the 'diode peculiarity'. Mosfets are basically designed to work in one direction only, and so using them with a.c. is only going to introduce added problems. For one thing, they will then not switch on/off properly as per general Mosfet rules ... and here in EC you would also need to put your load from its drain side over to the source side if you wished to see the Mosfet working similarly in both directions (there will not be the same action if you simply turn the Mosfet around whilst leaving the load on the drain in both cases). .... I would advise keeping EC Mosfets for d.c. only and aim to keep the Nmos Source connected directly to earth whenever possible.

The EC Mosfet allows such a reverse in the main ds channel, as a necessity for pulses etc which need an 'earth return' if they are to function correctly ... eg for cap discharge or inductor back emf simulation ... A real Mosfet utilises its body diode to allow for that, rather than using a main channel reversal path.

The above descriptions refer to ds a.c. .... your gate a.c. is a different topic, but that's for another time. Instead, note especially that it is pointless putting a diode across ds for EC usage, since the main channel is already able to conduct in reverse.... a pretend body diode serves no purpose for a proper setup of EC circuitry.

Mr 2cent and his decades of experience with practical circuit of mosfets: "Mosfets are basically designed to work in one direction only, and so using them with a.c. is only going to introduce added problems." You have no idea but must tell us this bullshit. This type of circuit is used 100Million times in Lithium Ion Battery management system and cause no problems. LOL

Mr 2cent, cant you just shut up if you have no idea what you are talking?

@Fraudz ... Real Mosfets with a body diode, yes ... but not here on EC where a reverse channel is used instead... like you said: EC Mosfets don't have a body diode.... yet still you use a pretend one, oblivious to the EC reverse channel usage ... lol

Mr.... tell us... what problems..... BMS have.... if they use.... mosfets in reverse..... or is it you..... having..... problems.... cause.... you never used mosfets..... in real.... shut the fuxk up if you have no clue..... Mr......

..... dont invent problem where no....... problems are..... imposter

The so called body diode exists because the MOS has in fact four terminals: gate, source, drain and bulk. There is no distinction between drain and source unless the bulk is connected to something, and usually it's connected to one of the two N regions (if we talk about a N-MOS), and that region becomes the source. In EC, apparently, there is no bulk consideration.

And this explains why we have no body diode.

@sircube, absolut correct!

Then how can I rely on EC giving me an accurate simulation of a MOSFET? Or can I not?

You can, but only for positive values of Vds (nMOS) or Vsd (pMOS)

@jason9 ... If you stick to d.c. when using EC Mosfets, and attach the Nmos Source terminal directly to earth (Pmos directly to main supply), then their circuit readings seen on EC comply with standard Mosfet mathematical formulae. The only thing you need to bother about from there, is setting the VTO (and Rds if you particularly want to, although that is not often necessary for full switching demonstrations). Here is a quick easy setup for an EC full switching mosfet:

Quick easy setup for an EC full switching mosfet: ..... Width: fully clockwise ...... Length: fully anti-clockwise ...... KP: fully clockwise (for Nmos) ....... KP: fully anti-clockwise (for Pmos) ...... VTO: 2v (this is the on/off Vth: set as reqd.) ....... Lambda: just ignore it ...... Put a 10k resistor from gate to earth (for Nmos) ..... Put a 10k resistor from gate to supply (for Pmos)..... Nmos Source arrow directly to earth..... Pmos Source arrow directly to supply..... The mosfet will then fully switch on/off when the gate volts crosses that VTO setting... The drain terminal Volts of the Nmos will then be seen to be lower than the gate terminal Volts, and the little bar of the mosfet will be fully visible (not just half out). This fully on state is called 'Ohmic'. Keep the supply positive.

The only datasheet details that you are likely to need are the VTO (Vth) and the Rds(on) .... more info about that here: http://everycircuit.com/circuit/5362558166106112

That is fairly restricted. What about if I just always keep Vds positive (for N-MOSFET) or Vds negative (for P-MOSFET) as @sircube says? Wouldn’t that work well?

You never need to talk in terms of negative really, eg for Pmos ... just take the absolute values of everything and life becomes much simpler when dealing with all mosfets. ... they can all then be talked about in the same positive way.... Anyway, let's stick to just Nmos for now, so that we don't even need to think about that. Try and get to grips with these few aspects: 1: You don't have to be restricted to putting the Nmos Source to zero, but it sure helps, because the Vgs is then just Vg (ie: Vgate - Vzero = Vg) ..... 2: Vgs -Vth is called the 'Overdrive voltage' ... Vov     ... Vov is used a lot, so get used to it. ..... Now: When Vds is less than Vov, the Mosfet is in an Ohmic state ... That means the mosfet bar is fully out and the mosfet is fully conducting as for a switch mode. So ... alter whatever you want, but aim to get that Vds less than Vov if you want full switching. (Notice again that if we keep Vsource to zero, then Vds is simply Vd ... ie: Vd -Vzero = Vds). So ... mess with any gate or supply voltages, and keep an eye on the Vds (ie on the drain terminal V). If you have followed all of this, then you will become quite familiar with altering either the gate V, or the Supply V, or the load resistor on the drain ... any of those to suit yourself, knowing that the Vds dropping below the Vov will enforce an Ohmic mosfet state which brings that little bar fully out to show a full switch mode current flow at ds. .... Sorry if it's long winded, but it's a real gem if you can get to grips with it. A formula will then ensue, but it would not mean much without understanding the above.

Ok, thx for your help.

@jason9 ... You're welcome. Let me know if and when you are happy with the above then we can discuss a formula. The formula will enable you to know how much V to apply at the gate in order to enforce the Ohmic switching for any Mosfet with a known Rds (rather than just crossing the VTO point in to the half-bar Saturation state)  ... and it works fine in EC. Similarly, it will tell you the Rds if you already know that pre-fixed gate V

I know you want to help me out and stuff, but I don’t really use formulas. Too much work. I just tweak the values till it works best. I know it isn’t a great way to set up circuits, but it’s worked fine so far and as long as I’m stuck with nothing but the simulator it’ll be fine. Once I’m out of the simulator and actually have real components to mess around with (and blow up) I can worry about Rds and formulas and math and stuff.

@jason9 ... That's fine. My opinion is that we should all enjoy the site and electronics at whatever level or interest type that we wish ... it's not a chore or an obligation. There are loads of aspects that most other users here (including yourself) know much more about than me. Friendship and encouragement are far more important than any knowledge.