# Voltage multiplier

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

1. ### stari

18
0
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

2,342
665
Jun 20, 2015
What is the current needed at 100V/10Hz ?

3. ### stari

18
0
Oct 24, 2015
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

5,364
771
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

2,950
803
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

2,496
718
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

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.