| Electronics > Projects, Designs, and Technical Stuff |
| 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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