Ok, first let me recap your desire, to make sure we are one the same page. You want a variable A.C. between 40Khz and 1.5 Mhz using a 555 in astable mode. You want a short duration spiked waveform, to drive a HV transformer.
This, at first glance, does not seem to be much of a prob. First, there are many 555 timer brands/types. They do not all share the exact same ratings. These break down into two major categories, Bipolar and CMOS.
The best specs I have found for a bipolar (NE555) have a maximum stable frequency around 500Khz in astable mode. However, the CMOS LM555C is rated as stable to around 3.0 MHZ. The CMOS cant source directly what you need current wise, but has the frequency capability. The bipolar can source the current you need, but lacks the frequency.
SOLUTION 1:
Use the CMOS 555 to drive a fast switching NPN, which sources enough current to drive a;
1. NPN power MOSFET. This will give you square wave 0v baseline DC.
2. A Triac with a separate A.C. supplied source, for A.C to the load.
SOLUTION 2:
Use the CMOS (or maybe a CMOS 556) split the output to drive a JK FlipFlop to invert the signal on one branch, and then join the two signals back together to form a square wave A.C. signal. (If I remember correctly.) Using paired NPN and PNP transistors and mosfets should do the trick.
Don't get me wrong, I am not an engineer, but a hobbyist who has built a square wave function generator using a 555, that puts out a better wave form on my B&K scope than my factory built B&K Function Generator does, and worlds better of a waveform than my el cheapo victor!
555's are anything but a "has been", though you have to consider their shortcomings, as well as their strengths. However, tell me of ANY component that isn't true of.
pauldude000
