Uses for Relaxation Oscillators

Discussion in 'General Electronics Chat' started by b2386, Feb 9, 2010.

  1. b2386

    Thread Starter New Member

    Feb 9, 2010
    Hi all,

    I am writing a technical paper for school in which I must compare two different relaxation oscillators and pick which one is better for a specific application. However, I am having difficulty finding where such a device is used. Google retrieves some general information but nothing too specific. Any info will be appreciated.
  2. sgardner025

    Active Member

    Nov 5, 2009
    We just did a lab at school where we used a relaxation oscillator to fire a SCR.
  3. Wendy


    Mar 24, 2008
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    Intermittent windshield wiper controls used a UJT relaxation oscillator to operate the relay that ran the wipers.
  5. Wendy


    Mar 24, 2008
    The neon circuit used to be used for road markers, due to their long life. Later they were exchanged for lamps that flashed, as opposed to staying on. Both are relaxing oscillators.
  6. KL7AJ

    Senior Member

    Nov 4, 2008
    Relaxation oscillators have been used in everything from Morse code practice oscillators to TV horizontal oscillators, and radars. They are used whenever you want a semi-regular period and aren't too concerned about a clean waveform.

    The most interesting application I've seen is a relaxation oscillator used for a comb generator for a PLL local oscillator. (This was used in an early 1960s National HRO-500 of the first synthesized receivers ever manufactured)

  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
    Real men don't need combs, either.:D
  8. Wendy


    Mar 24, 2008
    Except for their beards (I've seen your picture).

    Senior Member

    May 26, 2009
    Woah! I'm a man! :D

    My parents are always nagging me to comb my hair; questioning the fact of whether I stick my finger in the socket every morning! Need I say more?

  10. Darren Holdstock

    Active Member

    Feb 10, 2009
    There's a use right there. You can make a crude static electricity meter with a small neon bulb in parallel with a capacitor - hold one terminal in the hand, and wave the other in a static field, and the faster it flashes, the stronger the charge.

    I've seen neons used as ROs in cheap xenon strobe circuits too; they make for a very irregular time period that can be improved immensely by replacing the neon with a diac.

    I've designed capacitive discharge ignition circuits with a resistor, a cap and a SIDAC. The latter is a bit like a 2-legged triac that collapses to a very low impedance when a threshold voltage is exceeded. They can pass huge currents, wonderful things.

    Whatever happened to those 4-legged unijunction transistors? All I knew about them was that they made simple but effective ROs, and now they seem to have disappeared before I had the chance to use one in anger.
  11. studiot

    AAC Fanatic!

    Nov 9, 2007
    Can't say I agree with that one.

    What about an RC phase shift or Wein oscillator?
    These are RC feedback oscillators that require an amplifier.

    Not all relaxation oscillators require amplification or have feedback.

    A relaxation oscillator is basically a two state device configured so that achieving one state triggers a progression towards the other. The time spent in each state may be significantly different so the waveform can be highly asymmetrical. This characteristic brings about the most important uses of a relaxation oscillator. Either the short or long part of the cycle can be used.

    Raster scanning devices have a working long scan time followed by a rapid flyback time.
    Light flashers often have a long charge time at low current followed by a short intense discharge of light.