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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