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Date: Sun, 02 Dec 2018 17:38:58 +0100
From: DK7FC <selberdenken@posteo.de>
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In-Reply-To: <911f1e76-a994-c5d2-ef25-c4f7fde7d46f@n1bug.com>
Subject: Re: [Lowfer] LF: Re: FET change, hmmm
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Hi Paul,

In one of my early PA designa i also used an IR2110 to drive FETs having 
4 nF gate capacity. At 137 kHz the driver became quite hot and the total 
life time was just about 20 hours. In my opinion this driver is not a 
good choice for 137 kHz when using large FETs.
The ringing should be reduced by first reducing stay inductances and 
then maybe adding 1 to 5 Ohm in series to the gate. I spread the winding 
of the gates in my H bridge equally over the core and then twisted the 
two wires. Also i soldered them as close as possible to the FET, to 
reduce galvanic coupling.
73, GL, Stefan


Am 30.11.2018 21:50, schrieb N1BUG:
> All I know is this amp had very little drain ringing and worked well
> with FQA34N20 FETs but it is not happy with FQA32N20.
>
> I slowly increased drain voltage but at 200W out (of a kilowatt
> deck), there were obvious issues related to the ringing.
>
> I've gone back to my old faithful 200W output Class E amp for now. I
> am running WSPR-2 33% 137.437.
>
> Paul
>
>
> On 11/30/18 3:25 PM, Andy Talbot wrote:
>    
>> Cross conduction spikes can also be dealt with by inserting a bit of
>> inductance between top and bottom FETs of a totem pole, or in each leg of a
>> push-pull pair.  As done in the old Decca transmitters, and I cribbed for
>> my   700 Watt 137 design.
>> The inductor absorbs the short spike and returns the energy via clamp
>> diodes to the supply
>> See http://www.g4jnt.com/137tx.pdf
>>
>> A lot simpler than worrying about generating a special drive waveform with
>> gaps
>>
>> Andy
>> www.g4jnt.com
>>
>>
>>
>> On Fri, 30 Nov 2018 at 20:19, Hans-Albrecht Haffa<dk8nd@web.de>  wrote:
>>
>>      
>>> Dear OMs, dear Paul,
>>>
>>> To prevend current spikes by cross conduction of both fets it is necesary
>>> to use a gate drive circuit with dead time, as used in power supplies. But
>>> in this case there is a no current flow time in both transistors, what may
>>> cause spikes in the drain circuit. Damping of oscillations in the drain
>>> circuit may also reached by quiescent current, not used for class D PAs. To
>>> load the spikes to the load is not possible in an LW-PA, like in an
>>> flyback-transformer of an switch mode power supply, as the load is an
>>> LP-Filter that filters by reflections of the applied voltage.
>>>        
>