![]() ![]() MOSFETs do not suddenly transition from OFF to ON as the gate voltage rises, and teaching that to someone who doesn't know any better is just going to make them drive it incorrectly and needlessly destroy their parts. The Threshold Voltage only gives you the upper bound of the cutoff region, it doesn't tell you the lower bound of saturation. It is possible to use them in a digital manner by forcing them to always operate in saturation or cutoff, but in order to do that you need to know the analog boundaries between these modes and the linear region. The transition between "unambiguous day" to "unambiguous night" actually takes time, and between those states there will be a period of uncertainty when some people might say it's day, and others say it's night.ĭigital is an abstraction that we can use to simplify reasoning about certain kinds of systems that operate with specific constraints, but the underlying reality is always stubbornly and messily analog. Only if you ignore the time that sunrise and sunset take. Funny how can we know this when Vth cant be used for anything, according to you.ĭay and Night form a binary pair that we can use in reasoning If you want to knock it that's up to you, but dont tell me what is crap and what isnt because i wont believe you now, and i wont be able to believe you in the future either.īy your own statements, if you have a Vth of 5v then you cant use it for 'logic level' applications because it may only be 'on' by 1MOhm. I've had no trouble with this explanation since the late 1980's. I guess we cant have a reasonable conversation here as you think you know everything so go ahead, but dont tell me what to do because your wasting your time. Go and ruin your own devices if you want but don't peddle crap to beginners on this forum. The threshold voltage parameter plays no part in being able to determine if a FET can be used at TTL logic levels as a switch. ![]() That "conducting path" could very well have a resistance of say 1M, and that would not imply by any means the FET was on. However your leap that this means the FET is in any way "on" is something I would argue with. Interestingly though, 3.3v systems are becoming more and more popular. I do agree however that most of the time when we say "Logic Level" we mean some sort of 5v system like TTL or in more recent times CMOS. ![]() The threshold voltage, commonly abbreviated as Vth or VGS (th), of a field-effect transistor (FET) is the minimum gate-to-source voltage differential that is needed to create a conducting path between the source and drain terminals. We dont have to follow the action down to 4.99v, 4.98v, 4.97v, etc., because we can see that 5v clearly and that tells us something about the operation of the device.īut here is what Wikipedia has to say about it: Day and Night form a binary pair that we can use in reasoning, and do not have to go into detail about how we go from Day to Night or vice versa. You dont have to delve into the fact that the sun appears to rise slowly as the earth revolves. It doesnt matter that it really is or not, it matters what we take it to be in theory.įor example, if i say to you that i typed this in the 'day' or 'daytime' you can assume that i did not type it at night. It means that that 5v threshold is USED as a binary set. I dont like to see people leaving a place where things can be discussed that are usually interesting.Īnyway, the point of that 5v being a 'binary' threshold does not mean that the FET (or MOSFET) is a turn on or turn off device. I thought you may have left the board or something. It's actually good to hear from you, and i mean that sincerely. Did Snow White let you out of your cage again? He he, just kiddin'. HEY THERE Grumpy, havent heard from you in a while. Any other meaning of "logic levels" has to be accompanied by a qualifier. When used in isolation the words "logic levels" referrer simply to TTL logic levels. You might be but the rest of the world does not use that term to mean that. It is where the device STARTS to turn on. No, that doesn't happen even with a binary device, and as I said the FET is not a binary device. That is true, but it doesn't apply to a FET which is not a binary device. ![]()
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