Message-ID: <5C740794.1040902@posteo.de>
Date: Mon, 25 Feb 2019 16:19:48 +0100
From: DK7FC <selberdenken@posteo.de>
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References: <043bec62-8144-5ff3-98a6-9f04699f6a4c@no3m.net>,<5C73F86B.8080201@posteo.de> <1551107358099.3307@kuleuven.be>
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Subject: Re: LF: Class D current spikes
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...yes, might.
But also it might not, especially when the critical event happens only 
once per minute.

73, Stefan

Am 25.02.2019 16:09, schrieb Rik Strobbe:
> Hi Stefan, Eric,
>
> this might solve the PS tripping problem, but on the other hand it might also provide the MOSFET the draincurrent it needs to die ;-)
>
> 73, Rik  ON7YD - OR7T
>
> ________________________________________
> Van: owner-rsgb_lf_group@blacksheep.org<owner-rsgb_lf_group@blacksheep.org>  namens DK7FC<selberdenken@posteo.de>
> Verzonden: maandag 25 februari 2019 15:15
> Aan: rsgb_lf_group@blacksheep.org
> Onderwerp: Re: LF: Class D current spikes
>
> Hi Eric,
>
> What happens to the supply behaviour if you just switch some Cs parallel
> to the output, say 4x 4700 uF (low ESR) rated at 63V ?
> Maybe it solves the problem of the supply going into fault mode,
> although it is no the perfect solution.
>
> 73, Stefan
>
> Am 24.02.2019 13:08, schrieb Eric NO3M:
>    
>> I recently got a current mode (outp xfmr center tap not bypassed)
>> Class D amp going on 136khz, basically modeled after the W1VD / G0MRF
>> circuits.  FETs are 59N25s, 4820p / 10ohm snubbers, 5t+5t / 21t 3C90
>> 42mm output xfmr, 62uH (25t T157-26) choke.  Output xfmr depends on
>> the power supply in use:
>>
>> 30V linear supply: 5t+5t / 21t 3C90 42mm, 300W out
>> 48V switching supply: 5t + 5t / 16t 3C90 51mm, 500W out
>>
>> I am also using the G0MRF keying circuit, ie. P-channel MOSFET
>> (IRF9540) in the driver (MCP1404) supply line.
>>
>> If the driver is left active (key down), the beginning and end of the
>> input RF envelope produces a "clicking" noise... assume this is from
>> current spikes being developed and sunk by the FET body diodes?  If
>> the driver is keyed with input RF already applied, thereby
>> interrupting the drive to the FETs, there is no such behavior.  The
>> keying is shaped, resulting in a ramping of the driver supply voltage
>> and resultant gate waveforms to the FETs.
>>
>> These current spikes do not bother my 30V linear power supply,
>> however, when I attempt to use a 48V switching supply (rated at
>> 17.7A), it seems to be OK with the current spike generated on the
>> beginning of the RF envelope, but not the spike at the end of the
>> envelope and goes into fault mode.  If the driver is keyed with
>> continuous RF applied, it's happy and does not trip out.  But keying
>> the driver doesn't seem practical for digi modes without some exotic
>> circuitry or engaging computer generated signaling to key down *after*
>> RF drive is applied and key up *before* RF drive is removed.... again,
>> this phenomena only happens at the beginning and end of the input RF
>> envelope.
>>
>> Is there way to mitigate these current spikes, especially the one
>> generated when RF is removed?
>>
>> 73 Eric NO3M
>>
>>
>>      
>
>