Date: Mon, 25 Feb 2019 22:02:54 +0000
From: Chris Wilson <dead.fets@gmail.com>
Message-ID: <938269875.20190225220254@gmail.com>
To: N1BUG <rsgb_lf_group@blacksheep.org>
In-Reply-To: <56464634-818e-971a-cb3f-c38119106a14@n1bug.com>
References: <043bec62-8144-5ff3-98a6-9f04699f6a4c@no3m.net> <5C73F86B.8080201@posteo.de> <1551107358099.3307@kuleuven.be> <1516612920.20190225154808@gmail.com> <363e53a6-6235-9041-6db2-c9c163bb3df3@no3m.net> <56464634-818e-971a-cb3f-c38119106a14@n1bug.com>
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Subject: Re: LF: Class D current spikes
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Hello  Paul. everyone

A  series  of  overlapping  scope  captures  at end of WSPR
sequence  with  expensive  high  voltage  /  current  Wolfspeed  FET's
that usually survived, into the antenna and into a 10kW dummy load, taken
after  the choke and also at the drains of the W1VD amp. Driver TS-590
/  W1VD  doubler,  and W1VD amp ( end part of another circuit). U3S does
not show anything like this oscillating end to a TX sequence.:

http://www.chriswilson.tv/wolfspeed-choke-and-drain-50v-smps-antenna.zip

http://www.chriswilson.tv/wolfspeed-choke-and-drain-50v-smps-dummy-load.zip

Green trace drain, yellow after the choke.


Monday, February 25, 2019, 4:34:05 PM, you wrote:

> Chris, LF,

> Yes, although I run mine differently. I use the full output of the
> U3S into a doubler. I have run WSPR, JT9, and DFCW from the U3S
> without having any problems. I have also extensively used CW ID with
> the U3S and amp without problems. Yet both other exciters blow FETs
> at the instant RF stops.

> Chris, I know you are busy but if you get a chance I would like to
> see those scope captures. I thought I had it figured out that this
> is a voltage mode amp and should be seeing current spikes, but maybe
> I still have that wrong! If they are voltage spikes that may be
> easier to control.

> One thing I would like to learn more about is why do the drivers
> leave one phase high for a longer period than a half cycle when RF
> stops. What causes this? Is this only with specific FET drivers or
> are all of them prone to this?

> 73,
> Paul


> On 2/25/19 11:13 AM, Eric NO3M wrote:
>> Chris, et.al.
>> 
>> N1BUG relayed the same information regarding the U3S and class-D amp 
>> behavior, so your observation is not a one off...
>> 
>> 
>> 
>>>
>>> I have a series of scope captures from my W1VD amp showing huge
>>> voltage spikes on the FET drains at the end of WSPR and especially
>>> OPERA TX sequences. I suspected inductance was the cause. In fact I
>>> try not use OPERA at high power as i am pretty sure to kill a FET
>>> after a few sessions... Oddly (although I hope msomeone more
>>> knowlegeable has the answer), using WSPR from my U3S direct from CLK0
>>> of  th  Si535a  or  whatever it is never causes these spikes...  Or at
>>> least they are well contained.


-- 
Best regards,
 Chris                            mailto:dead.fets@gmail.com