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MOSFETs and Miller plateau

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Zero999:

--- Quote from: GigaJoe on April 06, 2019, 06:27:39 pm ---definitely,  so silly, made me laugh, never do anything in middle of the night

now instead 1 transistors, we need 3 to manage relay
hope it will work, now


--- End quote ---
Presumably R2 represents the relay col? It will work, but is a silly idea because it uses three transistors, rather than one and there's no back-EMF protection diode. :palm:

Use a single BJT.



--- Quote from: GigaJoe on April 06, 2019, 08:03:06 pm ---Gate threshold voltage 2.0V max, need some divider
with 3.3 , i think any logic mosfet will work, what the realy voltage ?    5V? or 12V


--- End quote ---
I haven't looked at the datasheet, but a voltage divider is only necessary if the gate voltage can exceed the maximum rating, which is normally between 15V and 30V. It has nothing to do with the threshold voltage.

GigaJoe:
sure,

 I base * h21 in saturation = Ic that really not enough for relay 100ma,   
it was discussed above

mosfet , read datasheet
VGS (th)Gate threshold voltage 0.6-2.0V  , where TC has 3.3V output

you may find-out a meaning for gate threshold here
https://en.wikipedia.org/wiki/Threshold_voltage

Zero999:

--- Quote from: GigaJoe on April 06, 2019, 10:11:05 pm ---sure,

 I base * h21 in saturation = Ic that really not enough for relay 100ma,   
it was discussed above
--- End quote ---
Yes, it was discussed above. The transistor doesn't have to go into complete saturation to turn the relay on. It just needs to turn on enough. The BC337 has a minimum hFE of 100, when IC = 100mA and VC = 1V.  A couple of mA of base drive is more than sufficient to turn on the transistor with <1V of voltage loss, leaving >11V for the relay.


--- Quote ---mosfet , read datasheet
VGS (th)Gate threshold voltage 0.6-2.0V  , where TC has 3.3V output

you may find-out a meaning for gate threshold here
https://en.wikipedia.org/wiki/Threshold_voltage
--- End quote ---
Sorry, I don't understand what your point is. It's still a silly idea to use three transistors when one will do. If you needed to control a much larger relay, i.e. a contactor, then ditch the MOSFET and put the relay's coil in place of R3.

Doctorandus_P:
If you ask me this should not have been posted in the "projects" section, but in the "beginners" forum.

I think it's a good idea to get a breadboard and som TO-92 sized MOSfets and BJT's and start experimenting untill you better understand the parameters of of these things.
There is no substitute for rolling up our sleeves and building something yourself.

I am quite familiar with MOSfet's, but had never heared of the "Miller plateau", but found it a quite intuitive name.
Typing it in a search engine confirmed that it is used more often, and that it is exactly what I thought it was.
 https://duckduckgo.com/?q="Miller+plateau"&ia=web

rbola35618:

Hi EEVblogger,

Here are two videos on the switching characteristic of mosfets and about the miller plateau.

It may or may no help but I put up here for your consideration.

Robert Bolanos


Mosfet switching characteristics 1


Mosfet switching characteristics 2





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