klugesmith wrote ...

jdub's circuit is for using a bare 2-terminal crystal (passive component). Change the crystal to change the frequency.
Sulaiman pointed to some crystal oscillator components, which are easier to use. Connect appropriate power voltage (3.3 or 5 volts) and get a corresponding logic signal out.
In both cases the frequency is fixed. Worst case frequency error of +/- 100 ppm (0.01%) is a pretty loose tolerance for crystal controlled oscillators.

Your 74LS624 is a voltage controlled oscillator chip. No crystal is involved, and you can tune the frequency over a substantial range. How are you planning to measure the frequency, if you don't have an oscilloscope? You could divide it down into the audible range (e.g. with CD4040 or CD4060) and listen with headphones or a small loudspeaker. Or adapt an old auto service dwellmeter/tachometer, which I could send you for cost of postage.

It's time you learned a little about logic IC's. Jump on in; they don't bite. Get a plug-in breadboard to play with -- apparently as popular now as they were decades ago. There are other forums to learn at.

Sulaiman wrote ...

I'm not sure exactly what you are constructing
but with Class-E (or any resonant circuits) if you fix your clock frequency
then every other frequency dependant circuit will need to be tuned to the clock.
It will be easier if you have a variable frequency clock
which would allow 'tuning' by varying the clock frequency rather than adjusting capacitance or inductance
at least for one tuned circuit.

I also doubt that a fixed frequency is best because tuned circuits vary their resonant frequency when loads/environment changes.
So,
Is there a reason to operate at exactly 4 MHz ?
How accurate and stable do you NEED the frequency to be ?

I would go for a simple variable frequency oscillator and an accurate frequency meter
(or estimate frequency from your oscilloscope)
or something like this digital sig.gen./freq.counter

many microcontrollers used to operate at 4 MHz - masses of info on the web
the 5v crystal oscillator that I linked to just needs 0v and +5v, and the output will drive the gate driver ic input directly.
I would not add any protection as the cost of an XTO on eBay makes it not worth the complication
e.g.
(look for TTL or HCMOS'output to be safe, some crystal oscilllators give a distorted sinewave of about 1v)

ZakWolf wrote ...


Perfect, thats exactly the information I was looking for. I am working on a class e tesla coil. I can check the frequency witht he scope no problem. I want to drive the FET's like this guy is From reading the site he doesn't seem to have a class e drive arrangement, just the X Mhz signal feeding the IXDD614 MOSFET driver which outputs the square wave to the FQA11N90 gate. With that setup I would need the GDT's or to match impedance,further more i wouldn't need the classe e mosfet drive stage before the final class e circuit like Erik has.. Or am I missing something.

Its hard enough for me to grasp all this without the added effect of high frequency and resonance messing with everything.

klugesmith wrote ...

Hi Zak.
Nothing wrong with plugging in components at hand to see what happens.
But that circuit, with your reported values of R and C, is not a crystal oscillator. It's a tunable schmitt-trigger oscillator that would run, probably better, if you omit the crystal. R1 and the C on left side determine the frequency. To shift the tuning range to higher frequencies, put a smaller C over there (or both of your 240-pF C's in series).

The schematic image you posted tells how to choose values for a better shot at making it a _crystal_ oscillator. In that mode it would oscillate at 3.6 MHz +/- 0.01%, a frequency insensitive to modest changes in R and C values. The table in the schematic might give the impression that C and R2 determine the frequency. No! Frequency is set by the nominal value marked on the crystal package. Then you choose C and R2 values from the table to make a functional oscillator. You would have to extrapolate to pick likely values to work with a 3.6 MHz crystal. Or use values posted elsewhere in this thread for use with 4 MHz crystals (close enough). Good luck!

[edit] the ringing in your scope picture is probably an artifact of power and ground routing to the oscillator components and/or the scope probe. Can we see a picture? What's the nominal bandwidth (not the sampling rate) of the scope? Does it have a menu option to artificially reduce the bandwidth?