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Re: [TCML] Need help with my first driver board for DRSSTC1

Hi Brian,

If your fiber optic system outputs active-low pulses, why don't you just
try adding an inverter after your receiver to get the correct logic
polarity? You know that (if it's assembled correctly) the driver schematic
you are using works, so if you minimize the number of modifications you add
to it, you reduce the risk of introducing a mistake. You've also got plenty
of extra inverters in your 74HC14, if I remember this circuit correctly.

In general, inverting the output of the flip-flop by connecting to Q_BAR
instead of Q will not get you the desired behavior (though I didn't trace
out an entire logic table for this circuit to see if it would work in this
case). I would also not trust what your multimeter is telling you when you
probe the input signals to the gate drivers and see some DC offset. Try
probing those signals with a scope instead to get a better idea of what's
going on. Either way, adding diodes or "filter capacitors" to the input
pins will only be fixing a symptom, not the actual problem that's causing
you to see that symptom. If your logic is wired correctly and you are
applying the correct test signals, there should be no DC offsets in your
logic signals. Furthermore, the little bit of "noise" that looks like
sinusoidal ringing that you're seeing in some places when you're probing
your logic signals is probably more a function of your probing technique
combined with your board layout than anything else (how much inductance is
there in the return path through your scope probe's ground clip? probably
quite a bit). Either way, it's not an issue at the moment because it
appears to be far below the noise thresholds of the logic gates.

I would also recommend either shorting out the CT inputs or applying test
signals from a function generator when you're verifying that your circuit
is working instead of leaving them floating. For example, the input node of
the 74HC14 that's squaring up the feedback CT pulses is a floating high
impedance node that could easily be picking up noise or crosstalk from
other parts of your circuit.

Good luck, and post some pictures!
(imo flipping through flicker to see your schematic, scope shots,
construction technique, etc. is a lot more efficient than watching a video
and scrolling back to the details you want to see)


On Mon, Jun 29, 2015 at 10:41 AM, Brian D <briandecosta38305@xxxxxxxxx>

> Hi everyone, I am new to this online community. I have enjoyed making my
> first 3 SSTC coils, the last one with a full bridge of 60n60s worked great.
> I wanted to try my hand at a DRSSTC. I am however having trouble getting
> the driver board to work. I am getting good square waves off the 47HC109
> pin 6 but I cannot get any square waves off the UCC373XX's. I have tested
> all the connections and they all look great.  Any help would be welcome.
> Here is the link for the youtube video showing the problem I am having-
> https://www.youtube.com/watch?v=Ig7FHaoqyfU
> thanks in advance for your help.
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