Fast enhancement mode [power] mosfet? - Page 1
Forum section: electronics / projects

author: madshaman
author_rank: Frequent Contributor
timestamp: June 27, 2013, 06:27:28 pm
content: Hi, has anyone encountered a series of mosfet that can handle 5-80 or more volts, can handle at least 150mW of power and whose total on/off switch time is in the 1ns range? Cheaper is better.Digikey's search tool only let's me sort by gate charge and input capacitance and such, it gets me a short list, but these values don't always relate directly to rise/fall time etc.Also looking for a beefier job which can handle 200-800V, tens of watts of power and can switch at the same speed.Best I've seen is around 10ns total on/off switching time.It's just for an idea I want to play around with. I've considered using RF fets, but they are pricier and piddlier.

author: madshaman
author_rank: Frequent Contributor
timestamp: June 27, 2013, 08:46:44 pm
content: I guess I'll also add that I know the real "switching" time is largely determined by both my gate driving circuit and also how quickly I can pump charge in and out of the gate and cool the mosfet if this turns out to be a lot of current.I'm just looking for some suggestions or series of mosfets I could look at (and order small quantities of). Ideally I want to go from  full on to  full off in the 800Mhz-1Ghz+ range. Are there power devices which can do this without the driving circuitry consuming huge amounts of power?

author: Kremmen
author_rank: Super Contributor
timestamp: June 27, 2013, 09:12:18 pm
content: I'm no expert when HF is concerned but reasoning from first principles what you ask for does not sound very likely. Gate charge is partly related to the physical dimensions of the gate structure. That in turn depends partly on the max current the main channel needs to pass. So, power fets have large channels -> large gates -> plenty of gate charge.Sure, you can find all kinds of fet from say Digikey that go to GHz and tens of amps but those would be amplifiers, not perhaps suitable for switching use...

author: madshaman
author_rank: Frequent Contributor
timestamp: June 27, 2013, 10:13:48 pm
content: I'm no expert either, so, best way to learn is to play.I do see the reasoning you're putting forth. The CoolMos series from Infineon seems to show some hope here.Since I'm no expert I'm wanting to order a bunch of "potential players" and do some circuit building and analyses, my 400Mhz scope will happily show a 1Ghz+ signal, but obviously the waveform will be distorted somewhat.I *do* have an ancient 20Ghz sampling scope too, so hopefully I'll learn a few things and gain some experience trying to push the switching frequency.Awful part is I need fast components for everything and parasitica are going to play a huge role. Also, solderleas breadboard is out of the question so this will probably be my first try at dead bug breadboarding a high speed circuit.I'll feel like a moron for a time, but with enough play, I'll probably learn a thing or two.

author: muvideo
author_rank: Frequent Contributor
timestamp: June 27, 2013, 11:01:36 pm
content: I've read about some new GaN mosfets that seempretty extreme in their specs.Digikey carries some EPC parts in their catalogue,check their datasheets, the package is a little"extreme" too

author: madshaman
author_rank: Frequent Contributor
timestamp: June 28, 2013, 06:27:01 am
content: Quote from: muvideo on June 27, 2013, 11:01:36 pmThanks, I just took a look, nice gate charge and capacitance specs; added to the short list!