Turning switch state at two different voltage

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Joined: Wednesday 06 December 2017 9:11
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Turning switch state at two different voltage

Post by tuoer » Wednesday 06 December 2017 9:41

Disclaimer: Sorry t my poor language, English is not my native language. I have a requirement to change the transistor/mosfet switch state at two different voltages.
Below is a small graphical representation. 3.3 v (red) to 4.5 (green). switch08 http://www.kynix.com/Parts/3231374/SWITCH08.html should be open when the voltage is between red line and Green. once the voltage reaches green switch should be close as long as it has not reached the red line level. Once the voltage had reached the red line switch should immediately open and should not close unless it has gone back to the green level.

i was thinking of schmitt trigger with transistor but could not get it. voltage can vary between 3.3 v (red) to 4.5 (green)


I managed to get what is needed with the following circuit, it is powered 4v power supply. following is the schematic. but could not get the upper and lower threshold voltage. currently i am getting 1.5v to 1.8v as threshold. Any suggestion for change in resistance value to shift the threshold to desired value between 3.3v and 3.9v (upper)
Update:fix my diagram
Figure 1. Required schmitt trigger operation. Output turns high when green level exceeded. Output turns low when less than red level.

There are many Schmitt trigger calculators available online such as one by Random Science Tools. Note that there are inverting and non-inverting versions.
The resistor value selection for comparator IC. Most IC has Vcc > 5v. My Vcc is limited to 4 v or lesser. I am using transistor for the design. CMOS comparator are quite expensive also not easily available at my place. I manage to design the requires circuit today but the threshold voltage is between 1.5v to 1.8v. I have used transistor schmitt trigger circuit. How do i shift the threshold volts higher?

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