I constructed a flyback power supply for nixie tubes (170-180V) using PWM to drive the FET and the comparator for feedback. I had good results with or without the MOSFET driver. I was using a IRF720. I don't know if Microchip specifies their driver in their app note to push sales or if it is truly needed. Since this was a one off, I left the driver in the final circuit. I did use MPSA42 transistors to switch the cathodes on the tubes. They have a lousy beta, so I imagine the FET would be more efficient as the high voltage regulator. If you try it out, let us know. On Wed, Jun 18, 2008 at 8:59 PM, William Chops Westfield wrote: > So for a while now I've had on the back burner a project intended to > add "dimming" capability to Electroluminescent "things" by permitting > user control of the frequency. > > The circuit looks very much like the HV switching regulator described > in the microchip Ap Note TB053 (http://ww1.microchip.com/downloads/en/ > AppNotes/91053b.pdf) (which was for nixie tubes), except that there's > an additional software controlled H-bridge stage that modulates the > HV DC into a pseudo-AC signal (just like the internal schematics of > many EL driver chips, except with higher voltages, variable > frequency, and more current.) > > But I've got a couple questions about the switching regulator part of > the circuit: > > 1) MOSFet or Bipolar? The app note uses a MOSFET, but I was planning > on using an MPSA42 bipolar transistor, which seems like it ought to > be sufficient for the relatively modest current requirements (perhaps > 10mA to 20mA at 100V?) Did I miss something? > > 2) if MOSFET, do I need a MOSFET driver? In this configuration, the > N-channel MOSFET is a low-side switch, so a generic logic-level > MOSFET ought to suffice, and I would have thought that the PIC's high > output current capability would have made it a pretty good MOSFET > driver all by itself. > > Thanks > Bill W > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist