Re: Is the CLK0 pin of si5361a supposedly up to driving an HEF4013 direct?

Chris Wilson

Hello Allison,

Thanks for the reply. What we are doing is driving this modified to
4013 flip flop, pair of IXD_614 fast FET driver IC's, 1kW Class D amp
direct from the Si5351a output via a 220nF poly cap. So what we are
seeing is the Si5351a is generating just enough to fire the 4013 but
it's far from ideal or reliable? What about using a logic level flip
flop like a 74HCT74? That should reliably and correctly trigger from
the Si, right? The LF version of the amp runs exactly as the build
notes later show, no issues. The MF version ran the FET driver mad
hot, with poor gate and drain waveforms, so we modded things...

The other thing we are seeing is unlike the ultra reliable, perfect FET
gate and drain waveforms on the similar LF amp, the MF one shows one
fairly decent gate and drain waveform on one pair of FET's, but the
other pair show incredibly spiky drain waveforms and poor gate
waveforms when power to the FET's is applied, into a good Bird water
colled dummy load or the antenna system. We have tried changing the FET
driver IC's over, tried replacing the driver IC's and the FET's even
to expensive ultra low gate capacitance ones, and tried swapping the
gate leads from the drivers to the FET's over but the same "side" of
the output shows bad waveforms. We also swapped out the 1500pF and 10
Ohm R1, R2, C3 and C4 components, and still the same side shows bad
waveforms. The transformer wiring is symmetrical, we even changed the
whole transformer T1 out to a newly wound one on on a different core
from the FT-240-79 one recommended, still one pair of FET's exhibit
the poor gate and drain waveforms.

but still the same side has bad waveforms... We can't see why this
should be... The circuit is as below in regard to after the FET
driver. We were using an HEF4013 flip flop and a pair of IXD_614 FET
driver IC's. The interconnections are pretty short. The FET driver to
FET gate wires are short and symmetrical.

Amp schematic link and info:

we use the W1VD LPF's for LF and MF.

A bit off topic and definitely not QRP but I do know a few here are
using U3S's to operate on LF and MF into Class D amps, so hopefully
not TOO off topic :)

Best regards,
Chris 2E0ILY mailto:chris@...

aK> BS170 and 2n7000 are not identical.

aK> While the 2n7000 can handle a bit more power it has higher capacitances
aK> and one has to watch the gate threshold.

aK> For class D and E one has to hit the gate hard as in 5-6V to insure the device
aK> is turned on hard (acts like a switch) and turned off hard.

aK> As to the HEF4013 you need the correct drive voltage to get the logic to switch.
aK> Generally using 3 or 3.3V logic (SI5351) to drive 5V CMOS is bad practice
aK> (also unreliable) and you need a level converter to go from 3V to 5V levels.

aK> Going down in frequency its generally easier to drive power MOSFETS
aK> so doing class D or E at 630m or 2200m is switch mode power technology.
aK> There are low cost parts that can easily hit KW power levels at 630M.
aK> You still need the right drive levels.

aK> Allison

Best regards, Chris Wilson (2E0ILY)

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