audioguru Posted June 12, 2004 Report Share Posted June 12, 2004 Power MOSFETs have a very low resistance from source to drain when switched on. But they also have a high gate capacitance. They can swich very quickly if their drive charges their gate capacitance fast enough.Is it true that the chip is simply thousands of little MOSFETs connected all in parallel? Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted June 12, 2004 Report Share Posted June 12, 2004 A high gate capacitance can be a misleading topic. I don't think that it actually charges like a capacitor, but exhibits the frequency response. I may be wrong. What is true is that the gate capacitance will keep the VGS from developing at a higher frequency. By the way, isn't the transfer characteristic of a MOSFET just nice. I like the way it keeps some predictability to the signal. Quote Link to comment Share on other sites More sharing options...
Cuckoo Posted September 12, 2004 Report Share Posted September 12, 2004 Hi everyone.Power MOSFETS do consist of many little MOSFETS connected in parallel. These are called "cells". For given die dimensions, companies will try to fit as many cells as possible (they connect in parallel so as to drop the drain - source resistance), while keeping a reasonable gate capacitance. What changes between companies is the cell structure (almost every company has patented their own - VMOS, SIPMOS, HEXFET etc), which will finally determine the gate capacitance as well. As for how the "gate capacitance" charges, it does so pretty much like a capacitor (the structure metal/polysilicon - SiO2 - Si, IS a capacitor), but does not follow exactly the curve. That's because there are other parasitic capacitances (gate - source, gate - drain, gate - body etc.) which also charge giving a slightly different curve.You might want to check out here:http://www.powerdesigners.com/InfoWeb/design_center/articles/MOSFETs/mosfets.shtmfor a more descriptive presentation on the topic. Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 13, 2004 Author Report Share Posted September 13, 2004 Hi Cuckoo,Thanks for confirming my theory.Good article. Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted September 14, 2004 Report Share Posted September 14, 2004 What do you suppose the gate capacitance amounts to. If they say it's in picofarad range, that is real low. I have seen picofarad capacitors and they seem much larger than the would be gate capacitance. So I wonder if the specification is intended for calculation purposes only. That is the voltage loss and behavior at higher frequencies. Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 15, 2004 Author Report Share Posted September 15, 2004 Kevin,Look at the datasheet for any power Mosfet and you'll see that its gate capacitance is thousands of picoFarads. Such a high capacitance requires a high current gate driver to charge and discharge the capacitance quickly, so that the Mosfet doesn't heat too much during its switching transitions. Quote Link to comment Share on other sites More sharing options...
Guest Yevgenip Posted December 6, 2004 Report Share Posted December 6, 2004 I read an article (Also in Scientific American) about Super-Transistors. It talked about super-quick transistors and extremly high-voltage resisotrs. 8)I'll post the article if someone is interested. :) Quote Link to comment Share on other sites More sharing options...
trigger Posted December 6, 2004 Report Share Posted December 6, 2004 Hi all,Check this out....... may be useful for this topicshttp://www.edacafe.com/books/ASIC/Book/CH03/CH03.2.php(or the whole free ebook at http://www.edacafe.com/books/ASIC/ASICs.php) Quote Link to comment Share on other sites More sharing options...
Dazza Posted December 6, 2004 Report Share Posted December 6, 2004 Hi Yevgeni P, yes I would be very interested in reading that article, please do post :D. Quote Link to comment Share on other sites More sharing options...
Guest Yevgenip Posted December 7, 2004 Report Share Posted December 7, 2004 I have a few trouble uploading, I'll post it soon then. Quote Link to comment Share on other sites More sharing options...
Guest Yevgenip Posted December 8, 2004 Report Share Posted December 8, 2004 Man, Why won't it send it??? >:( Quote Link to comment Share on other sites More sharing options...
Guest Yevgenip Posted December 8, 2004 Report Share Posted December 8, 2004 Lets try this step by step:-One:Facts_about_the_Transistor.pdf Quote Link to comment Share on other sites More sharing options...
Guest Yevgenip Posted December 12, 2004 Report Share Posted December 12, 2004 Two:From_Sand_to_Silicon_-_Manufacturing_an_Integrated_Circuit.pdf Quote Link to comment Share on other sites More sharing options...
Guest Yevgenip Posted December 12, 2004 Report Share Posted December 12, 2004 Three:How_the_Super_Transistor_Works.pdf Quote Link to comment Share on other sites More sharing options...
Guest Yevgenip Posted December 12, 2004 Report Share Posted December 12, 2004 Four:Microprocessors_in_2020.pdf Quote Link to comment Share on other sites More sharing options...
Guest Yevgenip Posted December 12, 2004 Report Share Posted December 12, 2004 Five:The_Future_of_The_Transistor.pdf Quote Link to comment Share on other sites More sharing options...
Guest Yevgenip Posted December 12, 2004 Report Share Posted December 12, 2004 Six!!!:The_Transistor.pdf Quote Link to comment Share on other sites More sharing options...
Guest Yevgenip Posted December 12, 2004 Report Share Posted December 12, 2004 At Last!!!! I am victor!!!! ;D Quote Link to comment Share on other sites More sharing options...
Dazza Posted December 17, 2004 Report Share Posted December 17, 2004 Thanks Yevgeni P :),very interesting, good stuff :D. Quote Link to comment Share on other sites More sharing options...
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