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oscillator

K

Ken O

Jan 1, 1970
0
Hello,

The 555 timer has a maximum frequency of 1MHz.
I would like to know if there is another chip that can go up to in the low
MHz ( about 20MHz).
I need a square output waveform. Basically a beefed up 555 :)

Thanks
ken
 
K

Ken O

Jan 1, 1970
0
CWatters said:
Do you need the extra functions that a 555 has? If you just need a square
wave can you use a crystal oscillator?

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

Ken
 
K

Ken O

Jan 1, 1970
0
---
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?

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
 
J

John Popelish

Jan 1, 1970
0
Ken O wrote:
(snip)
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.

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

Ken O

Jan 1, 1970
0
John Popelish said:
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
 
W

ws

Jan 1, 1970
0
John said:
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.

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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