This SMPS boosts low voltage (5-20 volts) to the high voltage needed to drive nixie tubes (170-200 volts). Be warned: even though this small circuit can be operated on batteries/low voltage wall-worts, the output is more than enough to kill you!
EagleCAD CCT & PCB files
MikroBasic Firmware Source
Step 1: How Does It Work?
This design is based on the Microchip Application Note TB053 with several modifications based on the experience of Neonixie-L members (http://groups.yahoo.com/group/NEONIXIE-L/ ). Get the app note - it's a nice read of only a few pages :
The illustration below is excerpted from TB053. It outlines the basic principle behind the SMPS. A microcontroller grounds a FET (Q1), allowing a charge to build in inductor L1. When the FET is turned off, the charge flows through diode D1 into capacitor C1. Vvfb is a voltage divider feedback that allows the microcontroller to monitor the high voltage and activate the FET as needed to maintain the desired voltage.