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Groups > sci.electronics.design > #429670 > unrolled thread

Gate resistor for lateral power MOSFET?

Started byFrank Miles <fpm@u.washington.edu>
First post2016-09-28 17:46 +0000
Last post2016-09-30 22:40 -0700
Articles 7 on this page of 27 — 7 participants

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  Gate resistor for lateral power MOSFET? Frank Miles <fpm@u.washington.edu> - 2016-09-28 17:46 +0000
    Re: Gate resistor for lateral power MOSFET? John Larkin <jjlarkin@highlandtechnology.com> - 2016-09-28 11:35 -0700
      Re: Gate resistor for lateral power MOSFET? Frank Miles <fpm@u.washington.edu> - 2016-09-28 22:22 +0000
        Re: Gate resistor for lateral power MOSFET? John Larkin <jjlarkin@highlandtechnology.com> - 2016-09-28 17:20 -0700
    Re: Gate resistor for lateral power MOSFET? Winfield Hill <hill@rowland.harvard.edu> - 2016-09-28 19:16 -0700
      Re: Gate resistor for lateral power MOSFET? Phil Allison <pallison49@gmail.com> - 2016-09-28 23:07 -0700
        Re: Gate resistor for lateral power MOSFET? Winfield Hill <hill@rowland.harvard.edu> - 2016-09-29 12:51 -0700
    Re: Gate resistor for lateral power MOSFET? Phil Allison <pallison49@gmail.com> - 2016-09-28 19:52 -0700
      Re: Gate resistor for lateral power MOSFET? Winfield Hill <hill@rowland.harvard.edu> - 2016-09-28 20:13 -0700
        Re: Gate resistor for lateral power MOSFET? Winfield Hill <hill@rowland.harvard.edu> - 2016-09-29 12:52 -0700
      Re: Gate resistor for lateral power MOSFET? Frank Miles <fpm@u.washington.edu> - 2016-09-29 16:41 +0000
        Re: Gate resistor for lateral power MOSFET? Phil Allison <pallison49@gmail.com> - 2016-09-29 18:52 -0700
          Re: Gate resistor for lateral power MOSFET? boB <boB@theresnoplacelikehome.com> - 2016-09-30 00:54 -0700
            Re: Gate resistor for lateral power MOSFET? Frank Miles <fpm@u.washington.edu> - 2016-09-30 15:57 +0000
          Re: Gate resistor for lateral power MOSFET? Frank Miles <fpm@u.washington.edu> - 2016-09-30 15:53 +0000
            Re: Gate resistor for lateral power MOSFET? George Herold <gherold@teachspin.com> - 2016-09-30 09:19 -0700
            Re: Gate resistor for lateral power MOSFET? Frank Miles <fpm@u.washington.edu> - 2016-09-30 20:04 +0000
              Re: Gate resistor for lateral power MOSFET? Winfield Hill <hill@rowland.harvard.edu> - 2016-09-30 14:07 -0700
                Re: Gate resistor for lateral power MOSFET? dplatt@coop.radagast.org (Dave Platt) - 2016-09-30 14:52 -0700
                Re: Gate resistor for lateral power MOSFET? Frank Miles <fpm@u.washington.edu> - 2016-10-01 17:29 +0000
                  Re: Gate resistor for lateral power MOSFET? Winfield Hill <hill@rowland.harvard.edu> - 2016-10-01 12:19 -0700
                    Re: Gate resistor for lateral power MOSFET? Frank Miles <fpm@u.washington.edu> - 2016-10-02 02:59 +0000
                      Re: Gate resistor for lateral power MOSFET? Phil Allison <pallison49@gmail.com> - 2016-10-01 21:10 -0700
                        Re: Gate resistor for lateral power MOSFET? Frank Miles <fpm@u.washington.edu> - 2016-10-03 00:20 +0000
                      Re: Gate resistor for lateral power MOSFET? Winfield Hill <hill@rowland.harvard.edu> - 2016-10-02 09:43 -0700
                        Re: Gate resistor for lateral power MOSFET? Frank Miles <fpm@u.washington.edu> - 2016-10-03 00:33 +0000
            Re: Gate resistor for lateral power MOSFET? Phil Allison <pallison49@gmail.com> - 2016-09-30 22:40 -0700

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#430076

FromWinfield Hill <hill@rowland.harvard.edu>
Date2016-10-01 12:19 -0700
Message-ID<nsp28701ud@drn.newsguy.com>
In reply to#430061
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

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#430124

FromFrank Miles <fpm@u.washington.edu>
Date2016-10-02 02:59 +0000
Message-ID<nspt5p$3p0$1@dont-email.me>
In reply to#430076
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)

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#430133

FromPhil Allison <pallison49@gmail.com>
Date2016-10-01 21:10 -0700
Message-ID<b7b9a0e0-8dd9-4fa4-b765-649db66dee70@googlegroups.com>
In reply to#430124
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

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#430167

FromFrank Miles <fpm@u.washington.edu>
Date2016-10-03 00:20 +0000
Message-ID<nss87k$dsu$1@dont-email.me>
In reply to#430133
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.
>  
>  
> 
> ....  Phil

Wow.  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.

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#430149

FromWinfield Hill <hill@rowland.harvard.edu>
Date2016-10-02 09:43 -0700
Message-ID<nsrdft01sd9@drn.newsguy.com>
In reply to#430124
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

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#430169

FromFrank Miles <fpm@u.washington.edu>
Date2016-10-03 00:33 +0000
Message-ID<nss91b$dsu$2@dont-email.me>
In reply to#430149
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!

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#430019

FromPhil Allison <pallison49@gmail.com>
Date2016-09-30 22:40 -0700
Message-ID<370f68e5-0157-463b-8b0e-ce5f1bd4f2a8@googlegroups.com>
In reply to#429928
cassiope wrote:

>
> > I assume you are not using source ballast resistors as most designs
> > leave them out. 
> 
> Actually I'd put some in :( figuring that they'd be convenient to measure
> the quiescent current.  Before I fixed my bias generator (using the
> thermal sense diode attached to one of the MOSFETS), the current wasn't
> as stable as I wanted so I bumped these to 0.22ohms.
>

** Using a diode like that could result in over compensation. 

   Lose the 0.22ohms, especially if they are WW types. 

> > 
> > ** Another option is to ground the sources of all the mosfets, 
> > via a common heatsink that can serve more than one channel.
> > This requires that the centre point of the PSU be available to
> > serve as the output as in this Haffler schematic:
> > 
> > http://bmamps.com/Schematics/Hafler/Hafler_9300,_9500_Schematic.pdf
> 
> I'd seen this design earlier - cute!  IIRC it requires (one? two?) separate 
> floating power supplies for each channel, unfortunately, which makes the cure
> probably worse than the disease in my situation.
>

** The main DC supply needs to be floating but drive can be from an op-amp running on +/-15V rails with centre grounded. Note how there are no load isolating components - not even an RC zobel. 



....   Phil

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