Chris
Thanks for the waveforms ... very informative. Sure looks like something is
triggering the input of the amplifier and thus causing the problem.
Since the problem doesn't exist with U3S's (which generates the various modes
internally) driving the amplifier (either directly or through a frequency
doubler) one has to wonder what the difference is between the U3S and the other
exciter setups that cause the problem. The fact that the U3S / amplifier
combination works correctly would argue that the 'problem' is likely not the
amplifier.
The one thing that the non U3S setups have in common is that the modes are
generated by software / computer / sound card. Think the first step in tracking
down the problem would be to see if there are any unexpected outputs from the
soundcard that are causing the problem. When you get a chance maybe you can
capture waveforms of the sound card output up to and after the end of a
transmission.
Assume that you have disabled all 'computer sounds' on the machines that are
supplying audio for the various modes?
Jay W1VD
----- Original Message -----
From: "Chris Wilson" <[email protected]>
To: "N1BUG" <[email protected]>
Sent: Monday, February 25, 2019 5:02 PM
Subject: Re: LF: Class D current spikes
>
>
> 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:[email protected]
>
>
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