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

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