[TCML] help needed! PSSTC

["McCauley, Daniel H" <daniel.h.mccauley@xxxxxxxx>]

Did you measure the gate waveforms as the MOSFETs directly using an oscilloscope probe?
What do those waveforms look like?
Is that voltage transient present on the output of the TL494 even when not connected to the TC4422s?

I've built many coils using the TL494 and have not seen this problem before.  Did you try swapping TL494 ICs?
Are you sure the transient you are seeing is "real" and not just due to poor probes or probe inductance?

Dan





Hello there! 

My name is jason and i am a first time
coil builder. my partner chris who has built a small coil before had used a kit from eastern voltage research to construct an audio modulated coil for a project, and we decided to take it to the next level for a project we are both now working on. we are using a design that is also from eastern voltage research but the kit we were interested in was no longer available because he was having trouble getting the PCB's for this particular kit. so we got ahold of the owner and had him send out the parts for his plasmasonic 2 kit and decided to try building it ourselves. 

We built a 12v power supply w an LM7812 and using this to power the low level electronics. this powers a TL494 which seems to be what most are using for this type of circuitry. out of the TL494 we are getting about a 13MHz transient off of the outputs of the TL494. this seems to be ok but as the signal then goes through the gate drivers, which are TC4422's, this transient gets reflected at the pulse and when it turns off. this is where our problem starts getting worse! obviously w these transient signals, the A/B h-bridge we are using to power our coil is firing the mosfet's at the wrong times. 

Both of us have experience w electronics and are both attending classes at UMO for a bachelors in electrical engineering technology, just so you have an idea of what skills we may have attained. we are attempting to integrate snubber circuitry to the gate driver outputs to reduce the noise for a smoother signal, but have not yet used them in any of the labs and/or projects we have taken on. i have attached the schematics that eastern voltage research provided and some pictures of our waveforms (1 of the gate driver outputs, and the rest are of the signal at the gate of the
mosfets) that we hope will spark some interest among the experienced coil builders of this forum. i signed up for the mailing list on this site and have enjoyed reading, and have learned quite a bit from the discussions here. we would appreciate any help that you all would have for us rookies.
It seems that through our experiences that this snubber circuitry should be placed in the h-bridge from gate to drain on all 4 of the mosfet's. i will be trying a number of different things, but we would really appreciate any advice! 

(FYI- we are building this prototype mostly on breadboard. the H-Bridge is constructed on PCB that we have soddered.)

Thank you for your time and i look forward to any response.
Jason Hill & Chris Geele
If there are any other pictures of the waveforms or the actual circuitry/breadbord/pcb that are needed i would be happy to post them

I wasn't able to post attachments of schematics or waveforms and the schematics are not available to the public as they are property of eastern voltage research....if you would like to see the schematics or the pictures i have i would be happy to send them to you. i was not aware that i could not use attachments on this mail listing. 

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