The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: Mike Monett
X-Mailer: Mozilla 2.02 (Win16; I)
Subject: Re: Comparator snap on-off ??
Date: Tue, 15 Oct 2002 18:14:20 -0400
NNTP-Posting-Date: Tue, 15 Oct 2002 18:14:19 EDT
Organization: Bell Sympatico
> I understand that the circuit requires hysteresis to function better
> and I have tried to apply it to the circuit. Applying it to the
> inverting input section works fine but when I try to apply it to the
> non-inverting input also it messes the inverting section up. The
> reference levels are provided by a resistor divider network and trim
> pots for fine adjustment. The input signal is provided by the ouptput
> stage of an op-amp that amplifies the thermistor being monitored. The
> level changes very slowly and as such causes oscillation at the
> transition points. What I am ultimately trying to find out is: How can
> I apply hysteresis to both sections at the smae time without
> interaction between the two?? Everything I have tried so far makes one
> section work as desired but not the other. Any ideas ??
As other have mentioned, filter the input signal to reduce the noise
pickup on long leads. The rc time constant can be long since your signal
is changing slowly.
You can add diodes to separate the effect of the positive and negative
hysteresis. These can be arranged to remove the hysteresis when the input
signal is between the limits, and become active when the input signal is
above or below the desired threshold.
Add a resistance to the positive lead of each comparator, and a diode in
series with a resistor from the positive input to the corresponding
The diodes make it easy to calculate the resistor values. Remember to
include 0.6V or so due to the diode forward drop. With care, you can have
make the positive and negative hysteresis values equal.
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup