Hi,
I am attempting to add hysteresis to a comparator input voltage level detector. For this I am using the following Reference Design:
http://www.ti.com/lit/ug/tidu020a/tidu020a.pdf
Page 7 of the above reference gives the design equations (equations 1, 2) for calculating the resistor values for a given high threshold voltage (V_h), low threshold voltage (V_l) and supply voltage (Vcc).
I am simulating such a comparator circuit in LTSpice, with Vcc = 12v, V_h = 5.64v and V_l = 1.4v. As there are only 2 equations and 3 unknowns, the designer must arbitrarily set one of the unknowns to some known value, before solving for the other two. I set Rx = 10k, which gave me Rh = 3.3k and Ry = 2.2k. I then constructed a simple comparator circuit with these resistors, a screendump of the LTSpice simulation is pasted below:
R1 is to pull-up the open collector output of the comparator. I am feeding a 50Hz sinewave, which varies between 0V to 8V into the comparator's inverting input. My problem is that the comparator is not switching low at V_h = 5.64v nor is it switching high at V_l = 1.4v, but instead maintains a constant 6v output, regardless of the voltage at the inverting input. I have also uploaded the LTSpice schematic for your examination.
Many thanks in advance!
I am attempting to add hysteresis to a comparator input voltage level detector. For this I am using the following Reference Design:
http://www.ti.com/lit/ug/tidu020a/tidu020a.pdf
Page 7 of the above reference gives the design equations (equations 1, 2) for calculating the resistor values for a given high threshold voltage (V_h), low threshold voltage (V_l) and supply voltage (Vcc).
I am simulating such a comparator circuit in LTSpice, with Vcc = 12v, V_h = 5.64v and V_l = 1.4v. As there are only 2 equations and 3 unknowns, the designer must arbitrarily set one of the unknowns to some known value, before solving for the other two. I set Rx = 10k, which gave me Rh = 3.3k and Ry = 2.2k. I then constructed a simple comparator circuit with these resistors, a screendump of the LTSpice simulation is pasted below:
R1 is to pull-up the open collector output of the comparator. I am feeding a 50Hz sinewave, which varies between 0V to 8V into the comparator's inverting input. My problem is that the comparator is not switching low at V_h = 5.64v nor is it switching high at V_l = 1.4v, but instead maintains a constant 6v output, regardless of the voltage at the inverting input. I have also uploaded the LTSpice schematic for your examination.
Many thanks in advance!
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