oscillator

Do you need the extra functions that a 555 has? If you just need a square wave can you use a crystal oscillator?

Of course, if you don't need it to be variable, a canned oscillator would do nicely.

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Rich Webb   Norfolk, VA

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Do you just need something where you can change the RC and get what
you want or do you need to have it be voltage controlled?

How stable does it have to be?

No just a square wave. Do crytals offer just as good square wave ?

Ken

Not that stable. Actually I wanted to swap that with my 555 chip (with minor changes too) and the output will go to my base of my 2n3055 transistor. At first I was looking the 7555, but that seems to be too much on the border line I dont really want to go digital too like a vibrator.

ken

Ken O wrote: (snip)

So, are you saying you want to switch a 2N3055 on and off up to 20 million times a second?

well the 2n3055 is only good for 3 MHz, I'll have to chosse another chip that does faster. even that , it IS better the 555.

Ken

I think the 2N3055 has a current gain bandwidth product of between 2.5 and 3 MHz. That means that it has a current gain of only 1 at 3 MHz. Are you planning to drive the base with the same current you hope to switch through the collector? You also cannot produce a 3 MHz square wave output that way, because the harmonics of a 3 MHz square wave are

9 MHZ and above, where the current gain is .3 or less. The 555 (as slow as it is) is faster than the 2N3055.

oscilators for higher frequencies are often built using schmitt inverters at these frequencies it's common to use a resonator or crystal to determine the frequecy rather than using a combination of resistor and capacitor.

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Bye.
   Jasen

Yes, do back up a few steps here. What solution or effect are you trying to rig up here, that needs a high(er)-current 20Mhz square wave?

Regards, ws

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change to leews to mail

square

Better. Run one at 40Mhz and divide by two to get a perfect 20MHz.

Sorry for delay in replying