Author Topic: Help with SSTC feedback circuits with 4046 IC and Schmitt Triggers  (Read 1687 times)

Offline davekni

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Re: Help with SSTC feedback circuits with 4046 IC and Schmitt Triggers
« Reply #40 on: September 30, 2021, 05:34:40 AM »
That screen shot shows the results plot of two signals.  Can you make a screen capture of the schematic (circuit diagram) also?
David Knierim

Offline AFreshLad

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Re: Help with SSTC feedback circuits with 4046 IC and Schmitt Triggers
« Reply #41 on: October 06, 2021, 08:08:50 AM »
Hi, sorry I didn't reply sooner, I have just been trying to design and test a new circuit.
The problem about the phase shift stuff before I realized wasn't a problem, I must of had a brain fart for 3 days before I realized that of course the voltage would shift 180 degrees as the 'voltage source' for the primary is not the MOSFET side but the transformer side during the off time. I scoped the current on the primary and saw that it remained mostly in-phase, but did shift enough such that during the turn-on event, it would switch whilst a reasonable current was flowing through the primary, which I think is causing the voltage spikes.

My solution for this is what I've been working on, and I chose to put a CT on the primary as well, and use the feedback from that to time the turn-off and turn on events, whilst the frequency feedback is still driven by the CT on the secondary. But if I continued using the 74HC74 D type flip flop for the interrupt controller, it would be very unstable as if no current was in the primary, e.g. at startup of it the turn off time is long causing the coil to ring down to zero, the coil would just refuse to turn on as no clock edges were fed into the flip flop to tell it to turn on the coil. So I had to redesign the circuit and created feedback that pulled a signal low at zero current and high everywhere else, hence allowing the coil to startup even if the current in the primary is 0. This means I would need an SR latch rather than a D-type flip flop, and I don't have any latches so I couldn't test the circuit on the tesla coil, but the feedback circuit works and produces a usable signal. I also had to add a delay circuit to delay the pulses to match the delay in the driver circuit. My only problem is my circuit is quite 'bulky', uses a lot of components for what I think is a simple task. If you have any better ideas that would be helpful. I attached the schematic below:

The 74HC74 flip flop is for the delay, as I couldn't get enough delay by adjusting the pots on the CT feedback.

Also, I'm bothering with all this rather than just waiting for the coil to ring down as the interrupt generator I'm using in an Arduino running the TMRPCM library, which plays music by using a carrier wave of 32KHz to artificially produce the analog audio waves, and thus the off times are very low.

Offline AFreshLad

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Re: Help with SSTC feedback circuits with 4046 IC and Schmitt Triggers
« Reply #42 on: October 06, 2021, 09:17:29 AM »
I made a mistake with the schematic, the flip flop circuit for delay won't work as it's edge-triggered, defeating the whole purpose of the rest of the circuit. So I now need a different delay circuit design that can delay the pulse by about 800ns. Any ideas will be helpful.
Thanks
« Last Edit: October 06, 2021, 09:26:35 AM by AFreshLad »

Offline AFreshLad

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Re: Help with SSTC feedback circuits with 4046 IC and Schmitt Triggers
« Reply #43 on: October 06, 2021, 02:26:00 PM »
I have just redesigned and built a new circuit which does successfully delay the signal whilst also keeping all the signal information by testing for both the rising and falling edge. However, the circuit is now very complex, and looking at other pulse delay circuits such as the 555 timer ones, its unnecessarily complex. The only problem is the 555 timer delay circuits I've seen delay by a large amount, about 100us, while I was a delay of about 800ns. Do you have any ideas on a simple delay circuit that keeps all the waveform information (as in if the signal in goes low, the signal out should go low and vise versa, rather than just using one rising edge to signal the pulses).
Thanks
I attached the new schematic below.

Offline davekni

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Re: Help with SSTC feedback circuits with 4046 IC and Schmitt Triggers
« Reply #44 on: October 07, 2021, 05:29:35 AM »
Schmitt inverter (HC14), series resistor, cap to ground, another schmitt inverter.  Rising edge delay will be a bit longer due to schmitt thresholds being a bit below VDD/2.  Fix that with a resistor in parallel with capacitor.
David Knierim

Offline AFreshLad

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Re: Help with SSTC feedback circuits with 4046 IC and Schmitt Triggers
« Reply #45 on: October 07, 2021, 08:35:45 AM »
I completely missed that idea. Thanks, I will try it, it should most like work much better than what I have now.

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Re: Help with SSTC feedback circuits with 4046 IC and Schmitt Triggers
« Reply #45 on: October 07, 2021, 08:35:45 AM »

 


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