AoE x-Chapters, 45 years of power MOSFETs

Winfield Hill wrote:

>   A new section from the AoE x-Chapters book,
>   for you to read, enjoy, and make comments.

Very interesting, but no depletion-mode power MOSFET like the IXTH20N50D 
is even mentioned? That's a pity.

	Best regards, Piotr

Piotr Wyderski wrote...
>
>Winfield Hill wrote:
>
>>   A new section from the AoE x-Chapters book,
>>   for you to read, enjoy, and make comments.
>
> Very interesting, but no depletion-mode power
> MOSFET like the IXTH20N50D is even mentioned?
> That's a pity.

 OK, depletion mode wasn't mentioned in the saga
 section, but it was plenty elsewhere, and cross-
 referenced.  It's also reasonably-well covered 
 in the main book, with Table 3.6 as well, where
 the IXTH20N50D is at the bottom of the table;
 the biggest, baddest part, the top of the heap.
 Piotr, have you used it for anything interesting?
 


-- 
 Thanks,
    - Win

On 7/19/19 5:53 PM, Winfield Hill wrote:
> John Larkin wrote...
>>
>> On 19 Jul 2019 09:56:28 -0700, Winfield Hill <winfieldhill@yahoo.com>
>> wrote:
>>
>>> A new section from the AoE x-Chapters book,
>>> for you to read, enjoy, and make comments.
>>>
>>> A 30-Year MOSFET Saga, The next 15 years,
>>> and Four kinds of power MOSFETs.
>>>
>>> https://www.dropbox.com/s/0qh8dxgielrkqvq/chap-3x.11_MOSFET-saga_2019-07-19.pdf?dl=0
>>
>> Who was it that made medium-power VMOS fets
>> before the IRF things?
> 
>   I think, Siliconix.  I have an old Siliconix
>   databook someplace, couldn't locate it just now.
>   Hardcover Siliconix MOSPOWER Applicatiosns book
>   is dated 1984, features IRF part numbers for
>   the more beefy parts.

Siliconix it was.  I went to a conference talk by one of their apps guys 
in early 1982.  They were really emphasizing the (then) good current 
sharing of parallelled FETs vs. bipolars.

Cheers

Phil Hobbs


-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

Winfield Hill wrote:

>   OK, depletion mode wasn't mentioned in the saga
>   section, but it was plenty elsewhere, and cross-
>   referenced.  

It is impossible to overpraise these niche parts.
Could you please just mention that their high-power variants do exist 
and let the reader google the details? ;-)

>   Piotr, have you used it for anything interesting?

Once upon a time I badly wanted to use a pair of them as an AC current 
limiter, but they turned out to be expensive unobtainium back then.
They would have had many advantages (e.g. they require no external power 
to start operation, while the enhancement-mode approach has the usual 
chicken-and-egg problem), but due to the empty stock I had to chose a 
more standard path.

I have 3 successfull applications you might find interesting enough:

1. Normally closed micropower "bleeder resistor" equivalent based on an 
IXTP08N100D2. This is to discharge the bus capacitor charged to 600V by 
a PFC stage. The current is set to the max level allowed by the thermal
capabilities of TO220 under continuous operation. If the powered
device (an FPGA, to be specific) fails for some reason, the bleeder 
steps in, otherwise it powers a tiny RF transformer wound on a 6mm core 
with a 1MHz square wave that produces the negative gate voltage, turning 
the bleeder off.

2. Active clamp transistor in a forward SMPS which operated at voltage
just within the allowed VGS ratings. Extremely simple gate drive, the 
same PWM signal used to drive the main switch and the depletion-mode 
FET. Maybe patentable, I don't really care.

3. Phase-sensitive AC zero-crossing detector made of two LND150 and
a coupled choke wound on an amorphic metal core. This is basically
an AC current source powering a coil with 1mA, so nothing spectacular 
happens there. Unless the polarity reverses and the "current source"
is no longer capable of providing constant current. Then the magnetic
field collapses and bang! -- there is a very narrow voltage spike
indicating the zero crossing. The second coil wound on the same core
transforms this rapidly changing magnetic field into a desired voltage
spike, say +/-2.5V. If the polarity information is a problem, just add
a full-wave rectifier to the output. The choke can be wound with a TIW,
so a substantial insulation level can be achieved. The LND150s in TO92 
can be put together along the flat part of the casing and then inserted
into the hole of the 12.7mm core. Then the entire isolated zero crossing 
detector would be composed of just 4 parts (2x the FET, a 1mA-setting 
shared source resistor and the "transformer" can fit within a circle of
diameter ~14mm.	

	Best regards, Piotr