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: [email protected] <[email protected]>
namens DK7FC <[email protected]>
Verzonden: maandag 25 februari 2019 15:15
Aan: [email protected]
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
>
>
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