Higher Freq 555 timer oscillator

Discussion in 'General Electronics Chat' started by CraigNS, Mar 25, 2012.

  1. CraigNS

    Thread Starter New Member

    Sep 23, 2010
    2
    0
    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
     
  2. w2aew

    Member

    Jan 3, 2012
    219
    64
    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
     
  3. CraigNS

    Thread Starter New Member

    Sep 23, 2010
    2
    0
    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
     
    Last edited: Mar 25, 2012
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