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'[EE]: How to generate high voltage symetrical puls'
2003\12\17@124558 by Dagmar C. Neto

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       Hi Piclist!
       I need to generate a low current high voltage (aprox. 80V), low
current symetrical pulse train, using a 6V or 9V battery. I've made some
experiences using a "inverted" power transformer and a signal generator,
but get no pulses out (looking in a osciloscope). The ideia is to use a PIC to
generate the pulses.
       I even did buy a low cost "training belt", to passive gymnastics and
muscle toner, but all that i see when looking at the circuit board is a bunch
of SMD transistors and resistors, and some caps (I've expected some
inductors or coils, at last)... and the silicon controller chip sealed by a black
plastic bubble.
       Someone can help me? Pointing the error or sugesting some
schematics...

       Thanks to all!

                       Dagmar

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2003\12\17@155026 by Peter Donahue

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Sounds like they've got a simple charge pump setup...



"Dagmar C. Neto" wrote:

{Quote hidden}

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2003\12\17@161139 by John N. Power

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> From:         Dagmar C. Neto[SMTP:.....dagmarcnKILLspamspam.....RC.UNESP.BR]
> Sent:         Wednesday, December 17, 2003 12:39 PM
> To:   EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
> Subject:      [EE]: How to generate high voltage symetrical pulses

>         Hi Piclist!
>         I need to generate a low current high voltage (aprox. 80V), low
> current symetrical pulse train, using a 6V or 9V battery. I've made some
> experiences using a "inverted" power transformer and a signal generator,
> but get no pulses out (looking in a osciloscope). The ideia is to use a PIC to
> generate the pulses.
>         I even did buy a low cost "training belt", to passive gymnastics and
> muscle toner, but all that i see when looking at the circuit board is a bunch
> of SMD transistors and resistors, and some caps (I've expected some
> inductors or coils, at last)... and the silicon controller chip sealed by a black
> plastic bubble.
>        Someone can help me? Pointing the error or sugesting some
> schematics...

     You can go wrong in two different directions. First, if the pulses are too short,
     they can be lost in the stray capacitance of the transformer or inductor. This
     is especially a problem if you are using 60 Hz transformers with microsecond
     pulses. Even audio transformers must be used with care. Second, if the pulses
     are too long (wide), and you are using high frequency switching power supply
     transformers, the core of the magnetic device can saturate before the pulse
     ends. This will cause differentiation of the pulse. In other words, only the edges
     of the pulse will appear in the output.
     If you are using a variable frequency and width pulse generator, you should be
     able to find some output from whatever transformer you are using. Once you have
     that, you can go from there to find the limits of that transformer. If you then need
     to go higher in frequency, move on to audio and then switching transformers. If
     you need longer pulses, move in the opposite direction.

     John Power

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2003\12\17@163428 by Samuel BOUQUET

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Is that for a 40khz or 200kHz App? (common ultrasonic sensor - big capa)

Sam

Dagmar C. Neto Wrote

       Hi Piclist!
       I need to generate a low current high voltage (aprox. 80V), low
current symetrical pulse train, using a 6V or 9V battery. I've made some
experiences using a "inverted" power transformer and a signal generator,
but get no pulses out (looking in a osciloscope). The ideia is to use a
PIC to generate the pulses.
       I even did buy a low cost "training belt", to passive gymnastics
and muscle toner, but all that i see when looking at the circuit board
is a bunch of SMD transistors and resistors, and some caps (I've
expected some inductors or coils, at last)... and the silicon controller
chip sealed by a black plastic bubble.
       Someone can help me? Pointing the error or sugesting some
schematics...

       Thanks to all!

                       Dagmar

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2003\12\17@181134 by Jinx
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> I even did buy a low cost "training belt", to passive gymnastics
> and muscle toner, but all that i see when looking at the circuit
> board is a bunch of SMD transistors and resistors, and some

Just as a BTW, I heard recently that these devices, when advertised
as muscle toners, in that never-ending quest for perfect abs, were
deemed a fraud and at least one company had to pay reparations

I have a similar device which is more along the lines of a biofeed-
back/physiotherapy machine, and is promoted as such, and that
does have small transformers. Unloaded it can put out very short
pulses at around 250VDC

Have you considered a pulse transformer, the type used to fire
xenon tubes, eg in strobe lights ? These take a HVDC pulse from
the mains (240V here) and boost it to around 4kV. Assuming a
10:1 or more step-up you might get what you want from 6V, should
get there with 12V

The other option might be a switching regulator (IC or discrete)
to get 80V and then chop it with a FET or transistor

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2003\12\17@211744 by William Chops Westfield

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On Wednesday, Dec 17, 2003, at 13:07 US/Pacific, John N. Power wrote:

>>         I need to generate a low current high voltage (aprox. 80V),
>> low
>> current symetrical pulse train, using a 6V or 9V battery.

There are driver chips aimed at powering EL backlights in this sort of
output range (80V P-P, 400Hz, typically.)
Try micrel, sipex, toko, or rogers corporation.  These typically
have a single inductor switchmode converter that generates about 40V,
and an alternating output switch to make the 40V be 80V P-P AC.

BillW

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