Hello,
I'm building a multi-channel TENS unit. I am wondering if one set of electrodes is going to affect another set if they're placed nearby each other. That is: should one channel (set of electrodes) be galvanically seperated from the others? Can this effect also be done using semiconductors, thus avoiding bulky/heavy transformers to provide galvanic separation?
Kind regards, rafe
Short answer, no. The transformers are very necessary, as you will not get the desired results at the bipolar sites if there is not complete galvanic isolation. I built many of these units back in the 70's when accupuncture was "in" and I used those 88 mh toroids you used to be able to get at the dayton hamfest. they were phone company overstock and could be had for about a quarter apiece. Merry Christmas, Tom
Those toroids were pretty large and are hard to come by these days. An alternative might be a common mode choke if there is enough isolation between the windings. A bit unorthodox and one must carefully consider core saturation but they are certainly a bargain.
I used one of those 88 mH torroids to replace a missing output/modulation transformer in a CVB radio back in the early '70s. That model had a reputation for sounding muddy because it cut off pretty bad above 2 KHz. The torroid went to about 20 KHz, and the crystal microphone picked up everything. It didn't sound like the same radio, after the repair. ;-)
Thanks Tom. I'll be using a CCFL transformer (with custom windings) at high-frequency to provide a DC +100V, then optocouplers to drive the output transistors. This way I can use a small core and not have to worry about slew rates, or generally speaking the transfer function of an output inductor.
K> > Hello,
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