AC voltage multiplier ?

[Externet]

How can AC voltage be doubled or tripled using no transformer ?

 

[Leftyretro]

How can AC voltage be doubled or tripled using no transformer ?

By using a combination of capacitors and diodes one can realize a voltage multiplier. However they usually can't be used to supply high current demand. Search fro voltage multiplier circuits and I'm sure you can find out the principle used.

Lefty

EDIT: Yea, I brain farted, no way this results in a higher AC output, only for DC.

 

[Externet]

Yes, thanks Lefty.
I mean AC in; AC out.

 

[Hero999]

You can't.

 

[duffy]

You could step it up with a voltage multiplier (Cockcroft-Walton generator) which makes DC, and then switch it to make AC.

 

[duffy]

You could also use a Marx generator sort of the opposite way to that: rectify the AC to get DC (at high potential), drive the Marx generator with that, HV pulses come out the top. Frequency isn't very stable, and it's really pulsed DC instead of a proper AC sine wave with no offset.

But it has no transformers. Matter of fact, there's no diodes, no semiconductors or vacuum tubes in the Marx generator itself - just capacitors, resistors and spark gaps.

Crazy old thing.

 

[MrAl]

Hi there Miguel,


There is also a sneaky way to do this


That is, build a series resonant circuit and take the output voltage
from across the inductor.
In other words, a cap in series with an inductor to ground, the input
ac voltage is applied between the cap and ground and the output is
taken from the center tap of the cap and inductor to ground.
This forms a 'filter' of sorts.
The esr of the cap shouldnt be exceedingly high, and the series
resistance of the inductor shouldnt be either.

For example, an 80uf cap in series with a 100mH inductor with 10 ohms
series resistance. Input voltage of 1v peak at 60Hz turns into 3v peak
ac. The output load can not be too great either, so 10k might get
you 3v peak but 1k might take that down to only 2v peak or even less.
You'd have to try a few values.

[FONT=Courier New]Vin(AC) -----cap------+------ Vout(AC)
                      |
                    inductor
                      |
       ---------------+----- ground

[/FONT]

The circuit works on resonant principles so has to be tuned.

 

[duffy]

Mr Al WINS 100 INTERNETS!!!

Technically an inductor isn't a transformer.

 

[MrAl]

Mr Al WINS 100 INTERNETS!!!

Technically an inductor isn't a transformer.

Hi Duffy,

What is 100 Internets?

Oh yeah, btw, as the inductor value increases the output voltage
increases also, but the sensitivity to fine tuning the cap and
inductor might get more critical. i'll have to whip up a few
equations for this.

 

[duffy]

Not sure. I helped a guy find a transistor one time and he said he awarded me a "hundred internets". Still waiting for them. I've been trying to figure it out by studying this diagram -

**broken link removed**

I'm guessing they got stuck in one of those tubes.

 

[MrAl]

Hi again Duffy,


Wow that's a neat pic depicting the internet he he

I wonder what happened to Miguel, he didnt come back to
comment on the more recent replies to his inquiry.

 

[duffy]

Probably got his homework answer. Hope he stuck around for the right one. Obviously your series tank is the correct answer, me and the other guys equated "no transformer" as meaning "no inductor", which isn't right.

 

[Hero999]

Besides it isn't a very good way of doing it, as soon as you add a load the Q drastically reduces which lowers the voltage.

 

[Willbe]

The Internet is a . . .

Series of tubes - Wikipedia, the free encyclopedia

 

[MrAl]

Besides it isn't a very good way of doing it, as soon as you add a load the Q drastically reduces which lowers the voltage.

Hi there Hero,


Well, dont you think that 'good' is relative here? It really depends on
the application. Light output currents and it works ok. Heavier
currents and the output is more limited...that's life...maybe
increase inductor value.
I also have not looked into the theoretical limitations that well.

Because it boosts the output and it doesnt use any transistors to do so
I think it is interesting that it works at all

BTW, i am still waiting for my 100 internets (he he)

 

[Externet]

No homework and still lurking...

Just looking if there was other alternative to mine:

A 12V AC (60Hz) supply line to split into 2 branches.
One branch feeds the input of a (subwoofer) audio amplifier, set to gain of 2.
The other branch feeds a full wave rectifier and filter -perhaps doubler, to supply DC power for the subwoofer amplifier up to a maximum of 2.8 times the input if the load allows.

The output of the amplifier could reach 24V then. No transformers. I think...

Miguel

 

[MrAl]

Hi Miguel,


Ok it sounds like you need a variable frequency boost or something.