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Electronics Forum / Basics / June 2006oscillator
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 > 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 :) Do you need the extra functions that a 555 has? If you just need a square wave can you use a crystal oscillator? >> Hello, >> [quoted text clipped - 6 lines] > 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 > >> Hello, > >> [quoted text clipped - 9 lines] > No just a square wave. > Do crytals offer just as good square wave ? Better. Run one at 40Mhz and divide by two to get a perfect 20MHz. Sorry for delay in replying >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 :) http://www.linear.com/pc/productDetail.do?navId=H0,C1,C1010,C1096,P2186 Of course, if you don't need it to be variable, a canned oscillator would do nicely. http://www.ecsxtal.com/pdf/ecs-200.pdf  SignatureRich Webb Norfolk, VA >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 :) --- 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? SignatureJohn Fields Professional Circuit Designer > --- > 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 (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? > (snip) >> Actually I wanted to swap that with my 555 chip (with minor changes too) [quoted text clipped - 5 lines] > 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 >>(snip) >> [quoted text clipped - 9 lines] > 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. 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. >>> (snip) >>> [quoted text clipped - 17 lines] > 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 Signaturechange to leews to mail > 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 :) 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. > Thanks > ken SignatureBye. Jasen |
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