The Greinacher-Schaltung

Voltage multiplication

Last time, I mentioned that by bringing (shielded) charge to the inside of a spherical conducting dome, we would obtain "voltage multiplication," and that in the circumstances discussed, this would deliver excess electrical energy.

In existing orthodox electrical technology, there is already a circuit known as a voltage multiplier, which will be the subject of this and the next post.

The Greinacher circuit

In 1913 Swiss physicist Heinrich Greinacher (1880 — 1974) invented an "Ionometer" — basically an ionization chamber and an electrometer. The latter needed 200-300 V dc, but only a 110 V ac supply was available. So he also invented the voltage-multiplying circuit called the "Greinacher-Schaltung" (Greinacher circuit), the basis of all diode-capacitor charge pumps. In 1951 John Cockcroft and Ernest Walton were awarded the Nobel Prize in Physics, having used such a diode-capacitor charge pump in their successful transmutation of atomic nuclei. This device is commonly known today as the Cockcroft-Walton voltage multiplier.

Fig 1. Cockcroft-Walton full-wave voltage multiplier (foreground) housed in the Department of Materials Science and Metallurgy, Cambridge University, built by Emile Haefely & Co Ltd, Basel, Switzerland in the 1960's. ref http://issuu.com/cambridgealumnirelationsoffice/docs/cam_66_lo_res/18

Energy analysis

The input from the energizing source to a Cockcroft-Walton circuit is a charging current at low voltage. Some descriptions imply that its output is essentially the same current at an arbitrarily high voltage, thus giving an arbitrarily high power gain, in theory at least. For example, Wikipedia says "One way to look at the circuit is that it functions as a charge 'pump', pumping electric charge in one direction, up the stack of capacitors." 

Fig 2. Circuit diagram of a three-stage half-wave Cockcroft-Walton voltage multiplier

However, there are obviously two paths by which current can flow back to and through the energizing source, shown as I₁ and I₂ in Figure 2. Now, the question still remains: what are the relative magnitudes of these currents? If current I₂ is not a lot higher than I₁, could the charge pump still possibly provide excess energy? Could it be an "energy multiplier" as well as a voltage multiplier?

I have tried to find a complete energy-based analysis of a Cockcroft-Walton multiplier, on-line or elsewhere. There are many analyses, mostly only dealing with charge building up from zero value, i.e. the initial transient situation, which is only of minor interest. Although some analyses discuss steady-state operation, few will discuss currents, and none that I've found will make any comparison of input and output energies or powers.

I'll look further into the energy analysis of the Cockcroft-Walton circuit next time.