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sharpie7 / circuitjs1

Electronic Circuit Simulator in the Browser
GNU General Public License v2.0
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How to simulate a depletion mode MOSFET like the RFP15P05 #867

Open alien999999999 opened 1 year ago

alien999999999 commented 1 year ago

I tried calculating the beta and i came up with 1.111 for this one. So i tried putting a P-channel mosfet, set 1.111 as beta, threshold -4V ; but connecting gate to 3.3V does not seem to pinch the voltage; but in reality it does work; unless i'm doing something wrong, of course: https://tinyurl.com/2q27ehfy

vindicatorr commented 12 months ago

You're farther along than I am (I'm only just now becoming aware of depletion/enhancement), but I found the older closed issue https://github.com/sharpie7/circuitjs1/issues/301 and you can pull the depletion FET code from there.

I'm just wondering where it even came from. When I export text (after removing everything but the fet), I can see the "f" is common ("(f)et"?), and the difference (other than position and fet values) is the 5th number (32 (enhancement) vs 9 (depletion)).

Again, I don't know where it comes from yet, and why we can't add it from the menu, or how much else we're missing out on that is already built-in but hidden.

Wait, that "9" wasn't enough. I had to change the 6th number to "-1" from "1" which I see was the threshold voltage. So negative whatever that number is.

Trying it again bare: N/Enhancement

$ 1 0.000005 10.20027730826997 50 5 50 5e-11
f 288 144 288 192 32 1.5 3

To: N/Depletion

$ 1 0.000005 10.20027730826997 50 5 50 5e-11
f 288 144 288 192 9 -1.5 3

Nope, that wasn't right. The arrow direction is different. Trying "8" instead of "9" (must've been "P" fet). Okay, that looks right now (https://circuitjournal.com/which-mosfet-should-you-use-with-arduino).

Mind you, I have no clue whether or not the underlying magic of falstad does what depletion is meant to do.

pfalstad commented 12 months ago

the 5th number is a set of flags.

32 indicates a body diode. Every new MOSFET you create has one by default. You can turn that off though. 1 is "P" type 8 is flipped (Swap D/S) 9 = 1+8 = flipped and "P" type

to make an N depletion mode mosfet, just use a negative threshold. to make a P depletion mode mosfet, use a positive threshold.

pfalstad commented 12 months ago

Sorry, alien999999999, for not responding sooner. The MOSFET model in this simulator is a very simple model. You're not going to get very good agreement with specific devices. In the future I might bring over a more complex model from spice.