Can rectification from ac to dc be done without diodes?

some told me it can be done with capacitors but i don't understand how

thanks in advance

 

In the absence of a schematic I find the claim of rectification with capacitors to be dubious. The essence of rectification is blocking the flow of current in one direction, while letting it pass in the other direction. AFAIK a capacitor cannot do that.

You could do it with a 2-element vacuum tube, which we used to call a diode before the semiconductor variety was invented.

Why would you want to do this? Diodes are so cheap as to be virtually free.

 

No, but there are many ways to make a rectifier, usually involving dissimilar materials. Selenium and Copper layered for example. A Schottky diode doesn't have a classic PN junction.

I read PB post after posting this, vacuum tube diodes are also a good way to go about it.

 

No, it can't be done with just capacitors.

 

If there was a DC offset in your signal (for example, a sine wave oscillating between 3V and 5V) you could use a capacitor to "bleed off" the AC and leave you with just the DC component (4V in this case), but that's probably not what you have in mind (and certainly wouldn't be considered rectification).

 

Mechanical rectification is possible by using a synchronous motor to drive a commutator/slip ring conbination. AC is fed to one set of brushes and DC is collected from the other set. It's a lot easier to use diodes.

http://en.wikipedia.org/wiki/Mechanical_rectifier

I almost forgot about Flame Rectification. Used as a safety device for proof of flame in furnaces. Look at the Best Answer link here..

http://answers.yahoo.com/question/index?qid=20060628050414AAJtTNt

 

also active rectification, with FETs or SCRs or the like.