On Fri, 30 Sep 2016 14:07:16 -0700, Winfield Hill wrote:> Frank Miles wrote... >> Frank Miles wrote: >>> [ snip ] >>> The breakpoint is around 1MHz, so distortion may be tolerable. >> >>Early testing looks very good! Stability seems fine with a few >>different loads, distortion (at least as viewed on the 'scope) is >>negligible, and BW and slew rates are at least twice as fast as I need. >>This is with gate resistors around 240 ohms (no beads, at least not >>yet). >> >>It would still be nice to have a better understanding of why these >>resistors are needed. For now I'll content myself with a fuller testing >>with more reactive loads. Hopefully that will shake out any weaknesses. >> >>Thanks Phil and everyone else that contributed to the discussion! >> -F > > I wasn't in the discussion, but would like to point out / remind anyone > interested, of my 200 W amplifier project of last fall. This has a > 1000 V/us slew rate and a DC to 10 MHz response (-3dB rolloff > frequency). > But ahem, it doesn't use lateral MOSFETs.I'm sorry, Win - I didn't recall that. I have no vested interest in the lateral MOSFETS. Is there a web link or at least a title that I might search for? Thanks!
Gate resistor for lateral power MOSFET?
Started by ●September 28, 2016
Reply by ●October 1, 20162016-10-01
Reply by ●October 1, 20162016-10-01
Frank Miles wrote...> Winfield Hill wrote: >> Frank Miles wrote... >>> Frank Miles wrote: >>>> [ snip ] >>>> The breakpoint is around 1MHz, so distortion may be tolerable. >>> >>>Early testing looks very good! Stability seems fine with a few >>>different loads, distortion (at least as viewed on the 'scope) is >>>negligible, and BW and slew rates are at least twice as fast as I need. >>>This is with gate resistors around 240 ohms (no beads, at least not >>>yet). [snip] >> >> I wasn't in the discussion, but would like to point >> out / remind anyone interested, of my 200 W amplifier >> project of last fall. This has a 1000 V/us slew rate >> and a DC to 10 MHz response (-3dB rolloff frequency). >> But ahem, it doesn't use lateral MOSFETs. > > I'm sorry, Win - I didn't recall that. I have no > vested interest in the lateral MOSFETS. Is there > a web link or at least a title that I might search > for?I don't remember the s.e.d. subject, and just now I couldn't find the folder I made on DropBox, for you s.e.d. blokes and a DIY-audio discussion, so I created a new one, see AMP-70A under s.e.d. https://www.dropbox.com/sh/mkoqdo5y0b9fevm/AACBM7iDdTyRLFADqLgj7ljNa?dl=0 -- Thanks, - Win
Reply by ●October 1, 20162016-10-01
On Sat, 01 Oct 2016 12:19:35 -0700, Winfield Hill wrote:> Frank Miles wrote... >> Winfield Hill wrote: >>> Frank Miles wrote... >>>> Frank Miles wrote: >>>>> [ snip ] >>>>> The breakpoint is around 1MHz, so distortion may be tolerable. >>>> >>>>Early testing looks very good! Stability seems fine with a few >>>>different loads, distortion (at least as viewed on the 'scope) is >>>>negligible, and BW and slew rates are at least twice as fast as I >>>>need. >>>>This is with gate resistors around 240 ohms (no beads, at least not >>>>yet). [snip] >>> >>> I wasn't in the discussion, but would like to point out / remind >>> anyone interested, of my 200 W amplifier project of last fall. This >>> has a 1000 V/us slew rate and a DC to 10 MHz response (-3dB rolloff >>> frequency). >>> But ahem, it doesn't use lateral MOSFETs. >> >> I'm sorry, Win - I didn't recall that. I have no vested interest in >> the lateral MOSFETS. Is there a web link or at least a title that I >> might search for? > > I don't remember the s.e.d. subject, and just now I couldn't find the > folder I made on DropBox, for you s.e.d. blokes and a DIY-audio > discussion, so I created a new one, see AMP-70A under s.e.d. > https://www.dropbox.com/sh/mkoqdo5y0b9fevm/AACBM7iDdTyRLFADqLgj7ljNa?dl=0 That was so nice for you to post this, thanks! I remember seeing it now, though I'd forgotten it before I began the project with the power amp requirement. One prominent note in your schematic warns about using the 1-ohm output apparently due to lack of protection. You may not have needed the low- resistance output (though that seems strange given the 5A - losing over 1kW is a lot of heat!) - but did you find that active shutdown schemes were too slow to protect your amplifier? (I haven't yet done this with my amplifier)
Reply by ●October 2, 20162016-10-02
cassiope wrote:> > > - but did you find that active shutdown schemes > were too slow to protect your amplifier? (I haven't yet done this with > my amplifier) >** And you won't need to. From the capacitance figures you quoted, I see you have gone for the high power "double die" devices rated at 200V,16A and 250W. Full protection only requires gate zeners of about 3.3V to limit current to about 5amps. In the event of high dissipation, when the chip temp reaches about 165C, max current falls preventing further heating and the device saves itself - amazing but true. .... Phil
Reply by ●October 2, 20162016-10-02
Frank Miles wrote...> Winfield Hill wrote: >> Frank Miles wrote... >>> Winfield Hill wrote: >>>> >>>> I wasn't in the discussion, but would like to point out / remind >>>> anyone interested, of my 200 W amplifier project of last fall. >>>> This has a 1000 V/us slew rate and a DC to 10 MHz response >>>> (-3dB rolloff frequency). >>>> But ahem, it doesn't use lateral MOSFETs. >>> >>> I'm sorry, Win - I didn't recall that. I have no vested interest in >>> the lateral MOSFETS. Is there a web link or at least a title that I >>> might search for? >> >> I don't remember the s.e.d. subject, and just now I couldn't find the >> folder I made on DropBox, for you s.e.d. blokes and a DIY-audio >> discussion, so I created a new one, see AMP-70A under s.e.d. >> https://www.dropbox.com/sh/mkoqdo5y0b9fevm/AACBM7iDdTyRLFADqLgj7ljNa? >dl=0 > >That was so nice for you to post this, thanks! I remember seeing it >now, though I'd forgotten it before I began the project with the power >amp requirement. > >One prominent note in your schematic warns about using the 1-ohm output >apparently due to lack of protection. You may not have needed the low- >resistance output (though that seems strange given the 5A - losing over >1kW is a lot of heat!) - but did you find that active shutdown schemes >were too slow to protect your amplifier? (I haven't yet done this with >my amplifier)Another CAD schematic version includes a fast shutoff scheme, but I didn't implement that on this prototype. The amplifier is (almost) fast enough to be a 50-ohm RF source, but the real usefulness comes from its high-current output, despite what the drawing says. We've been using two of them that way for almost a year, and nothing failed. Actually, we fried the electrode system, but the amplifier survived. Knock on wood. Using BJTs at high currents and high Vce invites disaster; the 180V 2SC4883A 2SA1859A have a much smaller SOA than I'd like. That's because they're small die parts with fT = 60 and 120MHz. We've been lucky so far. I also designed a fast SOA-sensing protection circuit, but haven't implemented that either. As it stands, the AMP-70A design is just a high-speed test bed. I have modifications extending its slew rate to 2 or 3kV/us. Keep up this kind of business long enough and eventually something will blow out! -- Thanks, - Win
Reply by ●October 2, 20162016-10-02
On Sat, 01 Oct 2016 21:10:31 -0700, Phil Allison wrote:> cassiope wrote: >> >> >> - but did you find that active shutdown schemes >> were too slow to protect your amplifier? (I haven't yet done this with >> my amplifier) >> >> > ** And you won't need to. > > From the capacitance figures you quoted, I see you have gone for the > high power "double die" devices rated at 200V,16A and 250W. > > Full protection only requires gate zeners of about 3.3V to limit current > to about 5amps. > > In the event of high dissipation, when the chip temp reaches about 165C, > max current falls preventing further heating and the device saves itself > - amazing but true. > > > > .... PhilWow. Too good to believe? Gonna have to check it. 3.3V zeners are so soft, but the NFB may hide some of that. Great observation, Phil, will have to check further.
Reply by ●October 2, 20162016-10-02
On Sun, 02 Oct 2016 09:43:41 -0700, Winfield Hill wrote:> Frank Miles wrote... >> Winfield Hill wrote: >>> Frank Miles wrote... >>>> Winfield Hill wrote: >>>>> >>>>> I wasn't in the discussion, but would like to point out / remind >>>>> anyone interested, of my 200 W amplifier project of last fall. This >>>>> has a 1000 V/us slew rate and a DC to 10 MHz response (-3dB rolloff >>>>> frequency). >>>>> But ahem, it doesn't use lateral MOSFETs. >>>> >>>> I'm sorry, Win - I didn't recall that. I have no vested interest in >>>> the lateral MOSFETS. Is there a web link or at least a title that I >>>> might search for? >>> >>> I don't remember the s.e.d. subject, and just now I couldn't find the >>> folder I made on DropBox, for you s.e.d. blokes and a DIY-audio >>> discussion, so I created a new one, see AMP-70A under s.e.d. >>> https://www.dropbox.com/sh/mkoqdo5y0b9fevm/AACBM7iDdTyRLFADqLgj7ljNa? >>dl=0 >> >>That was so nice for you to post this, thanks! I remember seeing it >>now, though I'd forgotten it before I began the project with the power >>amp requirement. >> >>One prominent note in your schematic warns about using the 1-ohm output >>apparently due to lack of protection. You may not have needed the low- >>resistance output (though that seems strange given the 5A - losing over >>1kW is a lot of heat!) - but did you find that active shutdown schemes >>were too slow to protect your amplifier? (I haven't yet done this with >>my amplifier) > > Another CAD schematic version includes a fast shutoff scheme, but I > didn't implement that on this prototype. The amplifier is (almost) > fast enough to be a 50-ohm RF source, but the real usefulness comes > from its high-current output, despite what the drawing says. We've > been using two of them that way for almost a year, and nothing failed. > Actually, we fried the electrode system, but the amplifier survived. > Knock on wood. > > Using BJTs at high currents and high Vce invites disaster; the 180V > 2SC4883A 2SA1859A have a much smaller SOA than I'd like. That's because > they're small die parts with fT = 60 and 120MHz. > We've been lucky so far. I also designed a fast SOA-sensing protection > circuit, but haven't implemented that either. As it stands, the > AMP-70A design is just a high-speed test bed. > I have modifications extending its slew rate to 2 or 3kV/us. Keep up > this kind of business long enough and eventually something will blow > out!That kind of speed from a power amplifier? Wow! The first vertical deflection amplifier I designed for a Tek 'scope only had ~10kV/us, obviously only for driving a well-defined load (deflection plates). I don't need this kind of bandwidth or slew rate for my current application. So far the lateral MOSFET design is simpler and considerably more compact. So long as I can make it reliable!
