Schmitt trigger output shape dependence on resistors values

Schmitt trigger thershold in a circuit

hi
from site: **broken link removed**
the subject is about schmitt trigger threshold. with looking the image( that i attached it), the below text is written:

The above diagram reproduces the basic Schmitt trigger circuit of Richard Piotter. It consist of two inverters (NPN and PNP) which give a double inversion to the input signal. The output of the second stage is fed back and summed with the input signal and a resistor to ground. Think of those resistors as forming a voltage divider which determines the input voltage required to cross the 0.6 V threshold of the NPN base emitter junction to turn the transistor on of off. With the values given the positive going threshold is 1.95 V and the negative going threshold is 1.34 V assuming a Vcc of 5V. The output signal at the PNP collector is non-inverting with respect to the input signal.


please explain to me how the values 1.95v and 1.34 are obtained?(the value of right -below resistor is 47 k)
thanks

hi
i see a circuit( attached) in net for schmitt trigger and i simulate it on ltspice.
in deriving the thresholds values of schmitt-trigger is concluded that the thershold values are independent of resistor values. so i changed the resistor values but the out put was changed. ( simulation results attached)
please explain to me whats the reason of changing output ?
thanks
View attachment schmit_trigger_opamp1_stim.pdfView attachment schmit_trigger_opamp1_schem.pdf

A usual simplification is to assume OP output saturation voltage being independent of output current. But that's not the case. In addition, an OP has maximum output current limits, e.g. implementing current limiting for overload protection.

With 200 ohm load resistance, the required output current is above specified 10 mA, surely no useful circuit dimensioning. I'm not even sure, if a real OP works with this resistor values. Try with factor 10 higher resistors and you see only moderate variation.

hi
i see a circuit( attached) in net for schmitt trigger and i simulate it on ltspice.
in deriving the thresholds values of schmitt-trigger is concluded that the thershold values are independent of resistor values. so i changed the resistor values but the out put was changed. ( simulation results attached)
please explain to me whats the reason of changing output ?
thanksView attachment schmit_trigger_opamp1_stim.pdfView attachment schmit_trigger_opamp1_schem.pdf

LT1013 is modeling a real amplifier, not an ideal. With too low resistor values the IC cannot maintain enough feedback current, because the output current of the amplifier is limited by the output short protection.
And threshold is not independent from resistor values, only the ratio of the resistor values doesn't matter, very important difference.
Try ideal OPAmp in LTSpice, you won't see difference.