Voltage multiplier

[stari]

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).

 

[dorke]

What is the current needed at 100V/10Hz ?

 

[stari]

What is the current needed at 100V/10Hz ?

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

 

[duke37]

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.

 

[Alec_t]

100V and 50mA can be LETHAL, especially for anyone with a weak heart or pace-maker!! You should take great care when using this.

 

[AnalogKid]

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

 

[stari]

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

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.