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LM111 Comperator Application

Idan Ozana
Intellectual 480 points
Other Parts Discussed in Thread: LM111

Hi,

I want to use the LM111 Voltage Comparator but in order to do so, I need you to clarify the following points (Attached Simulation):

1. Simulation is not pin compatible to the component datasheet (simulation missing pin 6: BALANCE/STROBE and pin 5: BALANCE).

2. How can I create hysteresis of ~2.5V and ~1V (I have 0V-5V square wave input)? Is it possible to do so if my load will be ~1k ohm? (My attention is to connect the LM111 output pin to cathode of the High Speed opto-coupler. The anode will be connected to 12V through 1kohm serial resistor)

3. Why 10V zener diode, become active at 6V? (Change the amplitude to 10V with DC of 10V)

4. Do you see any reason to split the R1 resistor into two resistors: before and after the zener (adding addition resistor next to the LM111 + pin)?

2313.Noname.TSC

Idan

  • 0
    TI__Guru**** 166196 points

    Idan,

    For hysteresis the output is feed back to the non inverting input through a resistor.
    Zeners can pass small amounts of current long before the rated breakdown voltage.
    I tried adding hyteresis in the TINA circuit, but it did not work correctly.
    I will test it in the Lab Wednesday.

  • 0 in reply to Ron Michallick
    TI__Guru**** 166196 points

    Idan,

    This circuit worked in the lab, but it did not simulate well. The output switchs states at 1V and 2.5V.

    The output swing at the 1k resistor will be 10.2V =  12V - 1.8V.
    The input trip point swing is 1.5V = 2.5V - 1V.
    So the attenuation from input to 1k resistor is 6.8 = 10.2V/1.5V, so I chose 10k and 58K (10/68=1/6.8)
    For the inverting input, I used Vin =1V and 1k voltage = 12V which is 1V + 10/68*11V (2.62V) on pin 3. 
    I added a divider to put 2.62V on pin 2.

     

    lm111.TSC