Galvanic seperation between channels in TENS unit

[rafe]

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

 

[t.hoehler]

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

 

[Joerg]

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.

 

[Michael A. Terrell]

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. ;-)


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[rafe]

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.

Kind regards,
rafe

t.hoehler schreef: