Hi,

I've been trying to create an oscillator using a 555 timer in astable mode. I want an output freq. of about 150 khz. Using a scope I can see as I start reaching the higher frequencis my ac waveform is left riding on a dc bias and by the time I get to 150 khz I'm only getting about 30 mv change in my oscillation and it's quite a messy sawtooth.

Is this just a limitation of some cheaper 555 timers? I've read online where people have used these for freq. up to 300khz.

Craig

 

The 555 really isn't suitable for frequencies higher than about 100kHz in many cases. If all you want is an oscillator - then a simpler and easier solution for higher frequency oscillators would be to make a simple inverter-based ring oscillator. See this appnote:
http://www.fairchildsemi.com/an/AN/AN-118.pdf

 

Thanks for your reply.

Ya, I knew I could make one with a schmidt trigger, but don't have one lying around. Maybe I can scrounge it out of something.. otherwise I'll have to order and wait.

Good to know about the 555 limitations I guess. Kind of slow really.

Another option I guess could be a frequency doubler... hmmm