LM331 hystersis resistor

Thread Starter

hasanferoz

Joined Mar 8, 2011
25
wat is the function of 47 ohms resistor imean how is it helping in improving the linearity i am talking abt the lm331 figure 3
 

wayneh

Joined Sep 9, 2010
17,496
Different mfgs publish different datasheets, and change them over time. You'll need to post the specific circuit or pdf you are looking at.
 

Ron H

Joined Apr 14, 2005
7,063
The 47Ω resistor causes a square wave to appear across it as the internal current source switches on and off. For example, if the reference current is 100uA (Rref=1.9V/100uA=19kΩ), then the hysteresis will be
Vhys=100uA*47Ω=4.7mV.
This ensures that the comparator switches crisply when the internal current source switches.
 

Thread Starter

hasanferoz

Joined Mar 8, 2011
25
i have one confusion is to why we want 4.7 mv as the hystersis voltage and what will happen if i increase or decrease i mean an i calculate the value of this resistor then wat parameter should i take into consideration
 

Ron H

Joined Apr 14, 2005
7,063
i have one confusion is to why we want 4.7 mv as the hystersis voltage and what will happen if i increase or decrease i mean an i calculate the value of this resistor then wat parameter should i take into consideration
I suspect that the exact amount of hysteresis is not critical, so long as you keep it well below the minimum input voltage. I think that a few millivolts hysteresis would be adequate. More might cause inaccuracies. I don't have real hardware experience with this part.
 
Top