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Re: LF: Class D current spikes

To: [email protected]
Subject: Re: LF: Class D current spikes
From: N1BUG <[email protected]>
Date: Mon, 25 Feb 2019 11:34:05 -0500
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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.

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