It is possible to use DC to DC step up voltage converter. It is possible to build it from basic elements, or to buy something ready to use, e.g.,

http://www.picoelectronics.com/dcdclow/peHVP.htm

Of course, it is impossible to get output energy higher than the input energy, so you may get 100V with a very low current.

It is possible to use DC to DC step up voltage converter. It is possible to build it from basic elements, or to buy something ready to use, e.g.,

http://www.picoelectronics.com/dcdclow/peHVP.htm

Of course, it is impossible to get output energy higher than the input energy, so you may get 100V with a very low current.

Than you very much

Like Nakhmani said, you can use DC-DC converters as it is possible to Step-up or Step-Down any given voltage at the cost of output current. Since the energy is conserved so power of system remains constant. You can use Texas Instruments controller TPS40210 for this purpose.

You can also use a boost dc-dc converter with adequat inductance at entry and capacitor in output.

But purely theoretically speaking, can't we build an oscillator circuit, use an inductor capacitor in series and in resonance to obtain hi voltage ac and use a rectifier to make it DC? It won't be a power supply though.

You can use a LLC-Converter

Make a simple oscillator and use a voltage ladder - two series-coupled chains of capacitors cross-connected by rectifiers. An old trick, but a good one.

Conventional way - Change 5 volt DC to Ac . increase AC to 72 volt AC - hange to DC . this always works-though sligtly expensive

Achkra, a charge pump will not work in DC. It needs AC to run and if your input is 5Vdc, you would need at least a twenty-stage multiplier, composed of 40 capacitors and 20 diodes. I would make a simple oscilator (using, for example, a 555), a transistor and a transformer. Then you´ll have a diode and capacitor to convert AC to DC in output. If yoy need precision on output, you could implement a feedback, using optocoupler.