GaN's datasheets missing td(on)/td(off)/tr/tf - Page 1
Forum section: electronics / projects

author: Free_WiFi
author_rank: Regular Contributor
timestamp: February 02, 2020, 03:36:39 pm
content: I'm looking at this Gan Transistor from the official website ofGaN Systems-GS-065-011-1-LMy trouble there's no specifications about these parameters :td(on)/td(off)/tr/tfIn the meanwhile these parameters are present on theInfineon transistorslike the :IGT60R190D1SSo what's the problem?Why there's no specifications about td(on)/td(off)/tr/tfon every GaN transistors from the official datasheets?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 02, 2020, 04:11:57 pm
content: They give Qg. What's it matter?Tim

author: Marco
author_rank: Super Contributor
timestamp: February 02, 2020, 04:40:08 pm
content: The design note has tr/tf measurements ... 90/10 10/90 looks about 10 ns for 400V 8A, delay a bee's dick.

author: David Hess
author_rank: Super Contributor
timestamp: February 03, 2020, 04:31:49 am
content: I agree with T3sl4co1l. The gate charge requirements matter more than the switching characteristics. Knowing the gate voltage waveform should be enough.

author: MagicSmoker
author_rank: Super Contributor
timestamp: February 03, 2020, 07:34:33 pm
content: Quote from: Free_WiFi on February 03, 2020, 05:21:46 pmThen don't mess with GaN transistors. Seriously, don't. Use a SiC MOSFET if you want bleeding edge tech without so much blood.

author: KaneTW
author_rank: Frequent Contributor
timestamp: February 03, 2020, 07:43:52 pm
content: It'd be more helpful if you specified what makes GaN difficult to use (low Vgs margin, layout challenges, ..?). Beginner is a sliding scale---I consider myself an amateur, but I still feel comfortable attempting a GaN design.

author: MagicSmoker
author_rank: Super Contributor
timestamp: February 03, 2020, 09:37:48 pm
content: Quote from: KaneTW on February 03, 2020, 07:43:52 pmI am rather busy at the moment but the three main reasons are:1. Very little margin between the threshold and maximum allowed voltages for the gate.2. No reverse blocking ability when off (except for very low voltages) and the voltage drop across the drain-source during reverse conduction is a minimum of the gate threshold voltage plus whatever negative voltage has been applied to the gate in a (misguided) attempt to help with turning/keeping it off.3. The low gate charge and extremely fast switching speed possible with GaN mercilessly exposes any inadequacies in your layout or circuit design, leading to incredible amounts of ringing, voltage overshoots and the like. If you can't make use of the main advantage of a new technology then why use it in the first place?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 03, 2020, 11:07:27 pm
content: Further still: avalanche ratings are nonexistent, and the active die area is considerably smaller than for other types.So, high power overload cannot be sustained for very long at all, and high voltage overload cannot be sustained at all.Voltage overshoot due to stray inductance can easily take up any headroom in the latter case. It's a good reason to use 500 or even 600V devices when the bus voltage is only 320V, say.Tim

author: Free_WiFi
author_rank: Regular Contributor
timestamp: February 05, 2020, 03:56:04 pm
content: Thank you people for your advicesthey are helping me to make some things more clear .... yet i got a lot of questions,but will solve them in the future.However i do yet need your help,because google search can't help me with this task scince it's to hard to make the killer point to get directly the aswer without wasting my days on internet.So basically,i'm searching an better alternative to theIRF 510.I need an Vds rating up to 200 volts (at least 250 or 300),fast switching for frequencies from 10/15Mhz up to 20Mhz (so thetd(on)/td(off)/tr/tfmust be on spec) and the rest of parameters not worse than these:Thanks.

author: magic
author_rank: Super Contributor
timestamp: February 05, 2020, 05:33:17 pm
content: What current? AOT1N60 has very low capacitances and reasonable internal gate resistance, but only good for 1A.Quote from: Free_WiFi on February 05, 2020, 03:56:04 pmThose specs depend on the drive circuitry and peak drain voltage so you can't compare them between different datasheets unless test conditions are the same.Watch out for the V/ns absolute maximum rating if you want to switch high voltage fast. This imposes a practical limit on the fall time, regardless of how "fast" the device inherently is.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 05, 2020, 08:58:37 pm
content: What are youreallydoing? There is no meaningful equivalent of a higher-voltage "IRF510" "switching" at 20MHz (which implies switching speeds of a few ns at most).GaN can do that, but it's in no way equivalent, and as indicated, is no beginner's project!Tim

author: ejeffrey
author_rank: Super Contributor
timestamp: February 05, 2020, 09:45:46 pm
content: Quote from: Free_WiFi on February 03, 2020, 05:21:46 pmBasically, FETs respond to electric field in the channel essentially instantaneously (at least compared to normal switching times). The turn-on time is mostly dictated by how fast you can stuff Qg into the gate. Rise/fall times are basically measurements of how much current you are driving into the gate.

author: Miyuki
author_rank: Frequent Contributor
timestamp: February 06, 2020, 09:02:40 am
content: Quote from: ejeffrey on February 05, 2020, 09:45:46 pmAnd if you want to use some tool for calculation try for exampleTI power stage designer toolit have FET Losses calculator, what can from transistor parameters and drive voltage calculate switching times and lossesI use it for quick check when choosing switching transistors

author: Free_WiFi
author_rank: Regular Contributor
timestamp: February 06, 2020, 03:08:50 pm
content: Quote from: T3sl4co1l on February 05, 2020, 08:58:37 pmMy diy projects are based onRF stuffandcoil induction heaterslike this :So for this reason i'm searching an better alternative to IRF 510 with higher VDS and super low capacitance.

author: Free_WiFi
author_rank: Regular Contributor
timestamp: February 06, 2020, 06:28:43 pm
content: Quote from: blueskull on February 06, 2020, 04:19:20 pmThanks youSo... i'm reading some book's (some are from soviet union and some are from united states) from 60's,70's and 80's and there's plenty of fun projects like :Plasma generator on mosfets;Radio amplifiers on mosfets;Portable desktop - super pocket welding power supply for precision welding + diy probe for the electrode;Analog arbitrary waveform generators on mosfet;Linear RF amplifier on mosfet;Precision Pocket Induction heaters for plugs welding/soldering like here :And so on... so basically as i'm interested in all of these stuff,for this reason i'm searching annor super cheap nor super expensiveMosfet which must be at least a little better on Vds and parassitic capacitanceP.S : I forgot to tell you,IRF 510 is not very good for the DIY of Metcal power supply,because of the low Vds wich is making it pretty vulnerable in that kind of system

author: Weston
author_rank: Regular Contributor
timestamp: February 06, 2020, 07:12:29 pm
content: Plasma / induction heating applications can have pretty widely varying loads, which can cause high efficiency zero voltage switching amplifiers, like class E, to lose zero voltage switching and cause the switching device to dissipate a lot more heat.Given that GaN devices have a small die and relatively high thermal impedance they are not the most suited to experimenting with this stuff, as they are easy to blow up with a load mismatch unless you have a really good heatsink setup and some sort of protection.Up to ~13MHz or so you can get away with smaller die size silicon MOSFETs intended for SMPS. Modern devices are a lot higher performance than the IRF510, just stay away from any "superjunction" devices, their output capacitance makes them unsuitable for class E applications.A few years ago I used two STP17NF25 devices in push-pull class E at 6.78MHz to supply ~250W of RF. If you want a specific part number to use, you could try that device. It has about ~3x the capacitance and 1/3x the on resistance of the IRF510 though, so it would be best for higher power levels.For higher frequencies you could use silicon LDMOS devices, they are a lot more robust than GaN devices and with careful design you can get comparable efficiency. They are decently expensive though. The MRF101AN would be similar to the IRF510 but with lower capacitance. I used it up to 40W at 40.68MHz in class E before with decent efficiencyhttp://superlab.stanford.edu/rfchallenge.html

author: OwO
author_rank: Super Contributor
timestamp: February 08, 2020, 04:57:55 am
content: Maybe consider class F as well.Class E: output is a high Q resonator; switch is turned on at voltage peaks and "drags" the waveform lengthwise to add energy to the resonator. Narrowband (<1% BW).Class F: output network is designed to have high impedance around the 3rd and 5th harmonic, and short circuit at even harmonics. Switch sees "soft" resistive load rather than a capacitive one, with device capacitance absorbed into the network. Can be designed for up to 10% BW.Using an ordinary LDMOS transistor (recycled cell tower ones will do) it's possible to get 70-80% efficiency at 100MHz with class F, probably higher at lower frequencies. Btw most 800/900MHz band transistors will work fine because the internal impedance matching is invisible below 100MHz. I personally use MRFE6S9125N a lot (~$5 refurbished).