Re: LF: Class D current spikes

[N1BUG <paul@n1bug.com>]

Thanks Chris.

After seeing those I wish I had a storage scope. There is much which
could be done to get to the bottom of what is going on with these
things. If I had the proper equipment I would do several things and
document the results:

1. Look at FET drains on both phases at the same time

2. Try that using every exciter at my disposal both into the dummy
load and antenna

3. Look at traces earlier in the system (FET gates, driver chip
inputs, doubler, exciter.

Those with more technical knowledge probably have additional ideas.

Clearly the amp is not handling end of RF envelope well but the fact
id does better with the U3S than other exciters seems to suggest
this problem starts earlier in the chain.

73,
Paul


On 2/25/19 5:02 PM, Chris Wilson wrote:
> 
> 
> 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.