Voltage Multipliers & Cockcroft–Walton generator

[BenTec]

Hello everyone, this is my first post in this forums. I will be posting more questions and stuff I am working on, I hope not to bore you guys too much haha =)

I have read wikipedia, but my question was not answered.

Now, with voltage multipliers we get high voltages ok. But at the expense of what? Or is there no loss?

Thank you in advance.
BenTec

[teslaproject]

Loss yes...advantage some

Hello everyone, this is my first post in this forums. I will be posting more questions and stuff I am working on, I hope not to bore you guys too much haha =)

I have read wikipedia, but my question was not answered.

Now, with voltage multipliers we get high voltages ok. But at the expense of what? Or is there no loss?

Thank you in advance.
BenTec

Bentec

Welcome. I do love these voltage multipliers and they are circuits which have their uses. To find out more about them just do a Google or Wikipedia search.
A brief answer to your question though....yes there are losses. Each step of the diode 'tree' throughout circuit will accumulate voltage drop depending on what type of diodes you use and this is because all diodes suffer forward voltage drop. Considering that the Voltage multiplier circuit has so many diodes, this can add up.
On the plus side - these circuits can replace bulky/weighty transformers and do a great job for specific applications. In parts they are cheaper than a transformer because copper wire is expensive compared to a handful of diodes and caps. It really depends what you are building.

That's it in a nutshell.

Regards

TP

[jibbguy]

Hi Ben.

Please excuse if this is overly simple and you know it already, or if it was not what you were specifically asking about. But hopefully then it may be helpful to others' some time

Regarding "Voltage Doubling / Multiplying" Circuits for Power Supplies:

Transformers (or simplified auto-transformers /coils) are the most common method of raising or lowering AC voltage for power supply applications... There can be significant losses with them, especially when DC is Inverted into AC by use of some oscillating or inverting circuit, then rectified back into DC once the AC waveform is at the desired higher voltage level. And of course there is no "free ride" with conventional Inductance; you can get higher voltage; but correspondingly lower current is the result (so the wattage is the same minus a little loss). Having a closely "AC Resonant" circuit helps with efficiency; but is tough to do when there are frequent load impedance changes.

The old passive "DC Voltage Doubler" / resistive ladder type circuits have a lot of losses (via heating resistors), and add problems regarding Grounding, because most do the "doubling by taking a circuit output from, say, "0 to 10V", to "-10V to +10 V"... lol not the same thing at all as "0 to 20V" in a grounded system... This means that using diodes, zeners, and other semi conductors can be a "tricky" design problem with them. I think this is why they are not very popular these days. Inverting into "AC", stepping up, then re-rectifying and filtering back to DC is more commonly seen; as there no quirky grounding problems to deal with.

Most AC-powered commercial electronic devices simply use a mains transformer with multiple Secondary taps; each winding supplying a separate power supply circuit with the specific AC voltage needed for the different required DC voltages. This is not true with Switching Supplies, but these are not used in consumer electronic devices as much as one would think; despite their being around 30 years now.

Using transistors, FET's, etc. is usually not very useful for voltage amplification in power supplies.... Because the CC power supply voltage must always be greater than or equal to the max V of the transistor's output... because they just cannot go above their supply V. That's why semiconductors are termed "current amplifiers" and not "voltage amplifiers" (...as the old vacuum Tubes were called). A transistor circuit can be made to help "amplify voltage" of course; but only by use of AC like through some dual push-pull arrangement where one is positive and the other negative ("Inverting" again), that can be fairly lossy too. And the old Tubes ("valves"), which are constant current devices that really can amplify "voltage" above their supply V, had very significant losses as well (and are harder to find now and were never known for being very reliable anyway).

Modern Switching PS' use pulse trains of a set amplitude that are Frequency and/or pulse-width controlled to get the desired DC voltage (after filtering). The are efficient, but more complex to make than a "Continuous" supply based on simple transformer and FWBR (full wave bridge rectifier) with only some added resistance and capacitance for filtering. Continuous supplies are less efficient power-wise, but simple and cheaper to make, and generally thought to be more robust in high-wattage requirements.

Modern consumer-grade Inverters of fairly small wattage (like they sell at K-Mart), are much more efficient than they were 20 years ago (but the really high current commercial ones, are still badly inefficient)... Often somewhere in the "90 percent" ranges. These can be used to step up 12 V DC to 120 RMS (which when rectified, provides about "86 VDC" if my memory is correct lol)... Or, the AC output from them is run to a transformer to get more or less V before going into a FWBR. Off the shelf battery changers can be used to power inverters, too. This all sounds "Kludgey" perhaps and not especially efficient... but "off the shelf", fairly cheap, and requiring less circuit design. Just don't try to run those "K-Mart" inverters past their Watts rating, they die quick.

For really high current applications, there is a point where it is less efficient to use a solid-state inverter circuit, than to use an actual mechanically-spinning dynamo powered by electric motor...Which generally have a lot of losses, too.

Depending on what voltage is desired (or the current / wattage needed), one of the most cost effective and efficient means of getting them is often using a computer desktop PC power supply. Cheap, reliable, fairly "beefy", with multiple outputs. Just remember that they need a load connected to operate properly.

And it is not unusual, in my experience anyway, for an Engineer to design a circuit around the voltages of an available supply

I think the easiest and obvious means of getting a specific supply DC Voltage, is by using a battery, or serial banks of batts... But the efficiency there depends on the charging circuit: When using fast sharp DC pulses to charge (ala John Bedini's work and products), it has been proved to be very efficient indeed. That is why, that circuits that inherently use these pulses anyway (such as Bedini's famous "School Girl" and others discussed here such as the "Ainslie Heater"), can be very efficient as the pulses can do "double duty" in helping to recharge the battery more efficiently than if either "straight DC", or 50/60 Hz "humps" were used (meaning the unfiltered output from a bridge rectifier, as many consumer car battery chargers are.. This is NOT "pulse charging").

There are some other very efficient means, such as "single wire" resonant coils, and similar Tesla-inspired inductive devices (such as Dr. Stiffler's work and what others like ~Imhotep~ have shown us with CFL's, one very successful Open Source project example seen on these Forums being "Joule Thief"). These are very interesting with great potential for extremely efficient lighting and other uses, but i suspect they are currently relatively difficult to design for meeting specific voltage & high wattage power supply requirements (especially for often-changing load impedance situations)... And they also tend to radiate RF which would eventually require shielding if building a commercial product. Hopefully, as we learn more about them, these inductance-based techniques could be used to provide "extremely efficient" lamp lighting to over a Billion people in Third World countries, who currently live in the dark, or who burn kerosene or other nasty things for light (... very unhealthy indoors)... As well as in developed countries to simply save a great deal of energy.

[BenTec]

Thanks for the your answer teslaproject and specially jibbguy for that monster explaination! I read it with great interest, thank you.

I've seen the other projects and im going to rebuild slayer007's thief. I'm very exited to investigate with it.

EDIT: Somone else told me for each double voltage = half ampheres. I knew this but I was not sure if that law was applied to everything. But it seems to!

Thanks again.