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Voltage multiplier

Discussion in 'General Electronics Discussion' started by stari, Feb 9, 2016.

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  1. stari

    stari

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    Oct 24, 2015
    Hello,
    i have a small project, where i must reach pulses cca 100V, frequency 10Hz, pulse width 5ms.
    My supply battery is 3.7V and i generate pulses with microcontroller.
    So, with a small transformer i can achieve 100V pulses, but the transformer is too big ! So i decide, to make a voltage multiplier, but,....have a little problems with this. Any suggestion?

    Thks from stari (Slovenia).
     
    Last edited by a moderator: Feb 9, 2016
  2. dorke

    dorke

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    665
    Jun 20, 2015
    What is the current needed at 100V/10Hz ?
     
  3. stari

    stari

    18
    0
    Oct 24, 2015
    Thks for quick answer.
    I need this device as TENS - pulses should be 1-50 mA on 1KOhm load. Some machines have higher current, but i think 50 mA is enough.
    Also i can control output pulse Voltage, from 1 - 3,7V.
    Stari
     
  4. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    You can generate the high voltage at high frequency (100kHz) so using a smaller transformer. This would need to charge a capacitor which would be switched to the output.
    A rough calculation, possibly wrong, would require a 10μF 100V capacitor to hold 50mJ.
    The size of the pulse transformer you are using will depend on how well it is designed for the job.
     
  5. Alec_t

    Alec_t

    2,892
    776
    Jul 7, 2015
    100V and 50mA can be LETHAL, especially for anyone with a weak heart or pace-maker!! You should take great care when using this.
     
  6. AnalogKid

    AnalogKid

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    665
    Jun 10, 2015
    Most TENS units have a small switching power supply. This can be a non-isolated boost circuit of a fully isolated flyback, but either way there will be magnetics involved and that means some bulk.

    Boosting 3.7 V to 100 V is a ratio of 27:1. At 90% efficiency (a very high value), that becomes 30:1, so for a 50 mA output you need 1.5 A of input current. Your duty cycle is only 1:20 and that helps reduce the input current, but this still will be a hungry power converter. Another option is to let the flyback pulse be the output by shaping it with a clipper. Much more efficient, but not a cookbook design.

    TENS units are very inexpensive and tested and safe, so why do you want to build one?

    ak
     
  7. stari

    stari

    18
    0
    Oct 24, 2015
    AnalogKid, i know, but i have such project to realize for my boss. (??). Ok, no problem, i will try by your suggestion.
    In fact, i will make TENS controlled by Android or iOS.
     
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