# calculating the thresholds for a schmitt trigger

Discussion in 'Homework Help' started by saksoook, Jul 13, 2011.

1. ### saksoook Thread Starter New Member

Jul 13, 2011
1
0
hello,
please i need help with analyzing this circuit it has a comparator with open drain output, so it acts as a schmitt trigger and i know that when the input is greater than the high threshold the output will be low (0 volt) but if the input is less than the low threshold the output will be high (5 volt) but the problem is i do not know how to calculate these threshold levels. you will find attached an image of the circuit. thank you. ​

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2. ### Georacer Moderator

Nov 25, 2009
5,151
1,266
I was actually examined on this today!

Suppose your comparator output is open. You can find the voltage on V+ if you analyze the divider formed by the resistances R1, R2 and R3 you can find the upper threshold. The divider has 5V on one end and 10V at the other.

Similarly, if the output is at 0V, do the same for the resistors R1 and R2, powered only by the 10V source. This will give you the lower threshold.