This circuit can generates 100V from 25V. The circuit is a typical flyback regulator that uses a couple of well-established circuit techniques to handle the high voltage. The first technique is to insert an n-channel MOSFET (Si4480) in series with IC1′s internal power transistor. The cascoded FET stands off the large switch voltage that arises when the switch turns off. The large switch voltage represents the input voltage summed with the reflected output voltage of the transformer’s primary. source

If you need to experiment with high voltage Tesla coil this is a best circuit that can generate voltage up to 100,000V.It is the solid-state Tesla coil.The spark distance up to 8 inch with a power-line consumption of 2A at 120Vac.The heart of circuit is SG3524 which is a pulse-width modulator controller.For the best efficiency the duty cycle is fixed at about 45% at the output frequency about 200-240KHz.source

The Supertex HV440 is used for implementing a pulse width modulated high voltage ring generator for telecommunication applications. The HV440 can operate in both closed-loop or open-loop. A closed-loop design is more complex but provides better load regulation and lower THD compared to an open-loop design.source

If you need a simple high voltage generator circuit here is your.The peak output voltage will be approximately 15,000 to 20,000 volts, but this will vary with the ignition coil type and the voltage at which the MOV starts conducting. Do not touch any part of the 555 circuit including any leads of the timing resistors or timing capacitor; doing so can inject interference into the circuit.source

High-voltage drive is useful for driving electrodes in many applications. The challenge is to boost the output of a conventional op amp to high voltages.This Design Idea presents a simplified ac high-voltage amplifier that uses complementary, cascaded NMOS and PMOS transistors.source