555 voltage output low

Discussion in 'General Electronics Chat' started by KLillie, Feb 14, 2015.

  1. KLillie

    Thread Starter Member

    May 31, 2014
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    I was trying to oscillate a 555@ 1MHz. My input voltage was about 8 volts, but my dc peak was around 1 volt. Later I saw that your run of the mill 555 doesn't like to be run much above 350 kHz. Could the frequency have been the cause?
     
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    "Could the frequency have been the cause?" The 555 won't operate properly above about 350KHz. You are trying to run it at 1000KHz. Yes, that is the logical conclusion? :)

    Ken
     
  3. ScottWang

    Moderator

    Aug 23, 2012
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    What is the oscillator used for and does it need to adjustable?
    If the oscillator is not adjustable then you could buy a 10Mhz crystal oscillator module and divide it by 5 and 2 to get a precisely 1Mhz has 50/50 duty cycle.
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    If the oscillator needs to drive only a very light load (a few mA) you could make one simply from a CMOS Schmitt gate such as a CD40106.
     
  5. ScottWang

    Moderator

    Aug 23, 2012
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    It can be done for 6 cheap signal source of square wave oscillators, just adding 6 RC and some 6 pots.
     
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    What?

    Ken
     
  7. ScottWang

    Moderator

    Aug 23, 2012
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  8. ScottWang

    Moderator

    Aug 23, 2012
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    Using One inverter or inverting Schmitt trigger to do the oscillator as this.
    You can using 74HC14 to generate the square wave.
     
  9. ian field

    Distinguished Member

    Oct 27, 2012
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    Apparently (allegedly) the CMOS 555 can do 2MHz, I was told the limit for a bipolar 555 was 100kHz but I'm sure I've had more than that from one - 350kHz isn't that far out if you're not too fussy about squarewaves actually being square.
     
  10. ScottWang

    Moderator

    Aug 23, 2012
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    The datasheet mentioned that the mic1555 can be oscillate reach to 5Mhz when it using RT = 1k, CT = 47pF, Vs = 8V, but I don't have this chip in hand, and it's quite expensive around US$1.23/ 1pcs in Taiwan online store.
     
  11. ian field

    Distinguished Member

    Oct 27, 2012
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    Past experience has made me wary of some datasheet claims.

    Years ago I bought a kit to build a Colour TV pattern generator, both timebases came from 555s - the 50Hz vertical timebase was no problem, but the 15.625 kHz horizontal generator was all over the place.

    The 555 is certainly capable of more than the PAL horizontal frequency, but its getting into the realms of stray reactances around the PCB getting significant compared to the specified values.

    After about a week of experimenting with ways to make the timebase stable, I just gave up and built a TTL timebase generator dividing down from 10MHz.
     
  12. ScottWang

    Moderator

    Aug 23, 2012
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    Using a 40Mhz crystal oscillator module, and get some counter IC as 74HC390, 74HC393, 74HC4040, and some dip switches, some divided by 2, some divided by 5, some divided by 10 then you can get a precisely oscillator.

    I used some crystal oscillator modules as 40Mhz, 32Mhz, 24Mhz and the above method to made a different kinds of frequency precisely oscillator.

    I also made a NE555 oscillator as below.
    [​IMG]
     
  13. KLillie

    Thread Starter Member

    May 31, 2014
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    Good info. Thanks, but I am going to start a new thread. I have a feeling this is going to get crazy.
     
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