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In Reply to: RE: A New Ultrasonic Heater posted by deafbykhorns on January 07, 2017 at 16:22:51
Before proceeding, I want to caution you and anyone else reading this about the lethal voltages involved. In addition to the usual precautions necessary when working with tube-type equipment, I urge you not to work with a circuit of this type without using an isolation transformer. "ONE HAND IN YOUR POCKET" WON'T PREVENT ELECTROCUTION if the circuit is powered directly from the AC mains without a transformer. Please remember this. It only takes a moment's distraction or inattention to be seriously injured or killed, and the risk is MUCH greater without an isolation transformer.
"The step down may be the tricky part, probably need to go custom."
The toroidal output transformer from the halogen lighting unit will work fine. It should output the same voltage as in the original design, roughly 30V pk-pk. I don't recommend attempting to perform the entire step-down to 2.5V or 1.5V in one transformer. The advantage of the new design (in addition to higher frequency) is that it will oscillate with no load. This allows attaching a second transformer onto the first for the final step-down. FWIW, the use of multiple transformers is a normal and accepted approach in broadband RF work for higher ratios, meaning anything more than about 4:1. I don't think it's possible to transform a 160V square wave to 2.5V in one transformer without losing considerable efficiency. That's a 64:1 ratio. Accomplishing this even with two transformers at 8:1 each can be tricky and may require transmission line techniques (multifilar windings) for good efficiency. Did you see my earlier post linking to the green cores? That's what I would use for the external transformer. Also, bear in mind that the first transformer is the only thing providing isolation between the output of the unit and the AC mains. It needs reliable, heat-resistant insulation between primary and secondary. Requirements for the second transformer aren't quite so rigorous.
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Buy Chinese. Bury freedom.
Follow Ups:
The second transformer works fine, I tried it with the halo supplies and it works fine. I got about 1.6v with the second toroidal playing around with the windings.Your circuit seems to work with a 24-48v rectified supply at the primary which would give some isolation and lower the voltage. Its not a perfect sq. wave but looks better than the Halo.
As triode_kingdom said, use an isolation transformer whenever possible as an extra precaution.
Edits: 01/09/17
I am with Triode. Would love to see a schematic with values and transformers you used.
I was wondering, because there are many halogen transformers out there, if using a additional step down might work on some if you loaded it with minimum rating?
Thanks Tom
Do you mean that you added an external transformer to the "standard" halogen supply? Mine wouldn't oscillate when I did that. Can you provide a few more details about the transformer and the work that was done?
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Buy Chinese. Bury freedom.
I just used another tube behind the first TX to get it oscillating.
Not practical but got the job done.
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