capacitor transformer

[Bob Monsen]

John Larkin wrote:

On Sat, 04 Jun 2005 20:04:52 GMT, Jamie Morken <jmorken@shaw.ca
wrote:


Hi,

Is there any application for using two electrostatically coupled
capacitors to make a transformer? Would changing the ratio of plate
area and plate seperation from the primary to secondary capacitor plates
be able to control the voltage input and output ratios? This
transformer would only be able to work with AC input just like an
inductor based transformer, the main benefit I can see is that it works
electrostatically so may not need an iron core to hold the EMF, and
should be good for high frequency?

cheers,
Jamie




If by 'transformer' you mean a gadget that transfers power efficiently
between source and load of different impedance, there's no direct
capacitive equivalent of a transformer.

The closest thing is a charge-pump inverter. You need at least two
capacitors: charge them in parallel and discharge them in series, and
you get the equivalent of a step-up transformer. There are lots of ICs
that do this for you. There's a newish part, TI or LTC maybe, that
adapts the number of caps dynamically to make a variable-ratio
inverter, which allows efficiency to be kept up, sort of like an
automatic transmission.

John

I was just reading about a 'capacitative transformer' for matching
impedance, used for resonant circuits. The idea is to make the source
see the parallel capacitance of two caps, and make the load see the
series capacitance.

However, I didn't think that was what the OP was interested in, so I
didn't post about it.
LOAD
AC source --- [50R] ---+--- [47.3pF]---+--- [2000R]---- GND
| |
[250.6pF] [63.6nH]
| |
GND GND

This is from "RF Circuit Design" By Chris Bowick. He calls it a Tapped-C
network.

---
Regards,
Bob Monsen

 

[Gert Baars]

Hello,

If this is ment for transforming
230V 50 Hz to a lower voltage e.g. 12V
just put a capacitor in series.
A too big value will blow up everything
secundary and a too small will deliver not
enough power.

I used 6uF (630V) bipolar in series
with a 60Watt lightbulb to make the
amount of light reducable.

Caution with this due to live voltage hazard.




Jamie Morken wrote:

Hi,

Is there any application for using two electrostatically coupled
capacitors to make a transformer? Would changing the ratio of plate
area and plate seperation from the primary to secondary capacitor plates
be able to control the voltage input and output ratios? This
transformer would only be able to work with AC input just like an
inductor based transformer, the main benefit I can see is that it works
electrostatically so may not need an iron core to hold the EMF, and
should be good for high frequency?

cheers,
Jamie

 

[Ratch]

"Jamie Morken" <jmorken@shaw.ca> wrote in message
news:EPnoe.1569435$Xk.504797@pd7tw3no...

Hi,

Is there any application for using two electrostatically coupled
capacitors to make a transformer? Would changing the ratio of plate
area and plate seperation from the primary to secondary capacitor plates
be able to control the voltage input and output ratios? This
transformer would only be able to work with AC input just like an
inductor based transformer, the main benefit I can see is that it works
electrostatically so may not need an iron core to hold the EMF, and
should be good for high frequency?

cheers,
Jamie

You can get a voltage gain of a few percent with a properly connected RC
network as shown in this old patent. The phase is frequency dependent
however. Ratch
http://patimg2.uspto.gov/.piw?Docid=02769088&homeurl=http%3A%2F%2Fpatft.uspto.gov%2Fnetacgi%2Fnph-Parser%3FSect1%3DPTO1%2526Sect2%3DHITOFF%2526d%3DPALL%
2526p%3D1%2526u%3D%2Fnetahtml%2Fsrchnum.htm%2526r%3D1%2526f%3DG%2526l%3D50%2
526s1%3D2769088.WKU.%2526OS%3DPN%2F2769088%2526RS%3DPN%2F2769088&PageNum=&Rt
ype=&SectionNum=&idkey=EADCC8C60169