LM311 Balance Pins

[dknguyen]

Does anyone know exactly how the two balancing pins work on the LM311 comparator? All the app note sfrom the all the companies seem to be copy/pasted from the same source and provide sample circuits but they don't ever seem to say what each balance pin actually does and how they interact with each other. (I'm trying to provide hysteresis without linking the inputs and outputs for positive feedback loops.)

 

[Roff]

Did you see Fig. 1 (on p.11) in the **broken link removed**? Read the accompanying text.

EDIT: Q5, along with R1, R2, R3, R4, and any external resistance you provide, in the National schematic forms current sources for Q1 and Q2. The Base-emitter voltages of Q1 and Q2 can be (un)balanced by adjusting these currents. That's what the balance circuit does. Positive feedback from the output to pin 5 also unbalances these currents, causing "offset voltage" in Q1 and Q2, which must be overcome by the input signal in order for switching to occur.

 

[dknguyen]

Did you see Fig. 1 (on p.11) in the **broken link removed**? Read the accompanying text.

Yeah I did. BUt I'm trying to minimize the number of components since I don't need offset adjustment and I am unable to separate out what does the offset adjustment and what is required for the hysteresis.

 

[Roff]

Yeah I did. BUt I'm trying to minimize the number of components since I don't need offset adjustment and I am unable to separate out what does the offset adjustment and what is required for the hysteresis.

Read my edit, although it probably won't help.

 

[Roff]

Yeah I did. BUt I'm trying to minimize the number of components since I don't need offset adjustment and I am unable to separate out what does the offset adjustment and what is required for the hysteresis.

I would start out by eliminating the 5k pot and the 3k resistor, then tweaking the 33k until you get the desired hysteresis.