Hysteresis....

Discussion in 'General Electronics Chat' started by Zsonali, Apr 3, 2014.

  1. Zsonali

    Thread Starter New Member

    Apr 3, 2014
    18
    0
    Hi All,
    What is the use of hysteresis? please explain....
     
  2. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
  3. sirch2

    Well-Known Member

    Jan 21, 2013
    1,008
    351
    Sorry but I disagree, hysteresis is deliberately built into most control systems. Consider a heating system controlled by a thermostat, without hysteresis when the room temperature was close to the thermostat set point it would be constantly tripping on and off which would wear out the mechanical parts.

    So hysteresis is built into the thermostat, it switches on at slightly lower than the set point and switches off at slightly higher, this means that there is a gap between it switching off after heating and switching on as the room cools.

    In electronics a schmitt trigger is an example of somewhere where you want hysteresis.
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,984
    3,722
    Probably the most common use of hysteresis is, as previous poster said, when you want to activate a control (logic, comparitor, op amp), at one voltage from "off to on" than the voltage required for "on to off" transitions.

    It helps in temp control to reduce short-cycle situations but it also reduces the impact of noisy signals on logic and comparitors.

    If you have a comparitor circuit with a noisy LO signal of 0-3 volts and a HI signal of 2-5 volts. You can use hysteresis (positive feedback) to insure the lo to high transition happens at 3.5 volts and high to low transition at 1.5 volts.
     
  5. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,127
    266
    I find that hysteresis is a hard concept to convey, I usually try to use something people can relate to physically to explain it.

    Snap-action toggle switches (mechanical hysteresis) are something we have all experienced, the idea that there are two different "snap points" that are not the same turning on or off is easy to grasp.
     
  6. Zsonali

    Thread Starter New Member

    Apr 3, 2014
    18
    0
    Thanks all..... I have something to share.....
    Lets say we have a reference voltage 5 V for a comparator. Now whenever the input to the comparator exceeds 5 V, then only we will get a high at the out put. Now if anyhow, my input contains ripple, then there comes a condition when my input may go below 5V say 4.99 V, then the output is not high but low, then again when my input reaches or exceed 5 V, then my output is high. So, this is the reason why we see a glitch at the output. Now to suppress this to happen, we generally use hysteresis. Where we can change our reference, so that whenever there is a ripple in the input, circuit should not be confused with the glitches..... This is how the Schmitt trigger circuit works..... and that's why we use hysteresis.
    You can write your concerns if I am wrong somewhere....

    Thanks to all !!!!!! :)
     
  7. sirch2

    Well-Known Member

    Jan 21, 2013
    1,008
    351
    Sounds like you have got it
     
  8. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
Loading...