I am wanting to calculate the hysteresis of a non-inverting Schmitt Trigger using a LM358 on the circuit below:

According to the resistor/voltage divider, the voltage drop across R1 will be about 8.16 volts and the reference voltage at node A will be about 3.84 volts (12v minus 8.16v)

The voltages at node B will vary between 0 volts and 6 volts.

I have found the links below to calculate the voltage high and voltage low outputs.

1. http://www.pcbheaven.com/drcalculus/index.php?calc=st_nonsym_sp

2. http://hyperphysics.phy-astr.gsu.edu/hbase/Electronic/schmitt.html#c2

3. https://howtomechatronics.com/how-it-works/electrical-engineering/schmitt-trigger

Using the boxes in link 1 and using values of 'Supply voltage' = 5 volts, R1 = 10k, R2 = 10k, R3=10k

I am getting:

V High=

V Low=

and using the same values 'Supply voltage' = 5 volts, R1 = 10k, R2 = 10k, R3=10k in link 2

I am getting:

the trigger voltage will be

= 3.3333 Volts

and it will hold until the signal drops to

= 0 Volts

When I enter values into these input boxes on these websites I am getting different results or am I missing something!?

So if I use the boxes in link 1 for my circuit ..that is Supply voltage = 12, R1 = 10k, R2 = 4.7k, R3 (RFB) = 220k

I get..

V High=

V Low=

whereas when I enter the values in link 2 I get...

V2 =

V'2 =

Also I do not understand what the '

look under

can someone enlighten me?

So basically what is the correct formula?

According to the resistor/voltage divider, the voltage drop across R1 will be about 8.16 volts and the reference voltage at node A will be about 3.84 volts (12v minus 8.16v)

The voltages at node B will vary between 0 volts and 6 volts.

I have found the links below to calculate the voltage high and voltage low outputs.

1. http://www.pcbheaven.com/drcalculus/index.php?calc=st_nonsym_sp

2. http://hyperphysics.phy-astr.gsu.edu/hbase/Electronic/schmitt.html#c2

3. https://howtomechatronics.com/how-it-works/electrical-engineering/schmitt-trigger

Using the boxes in link 1 and using values of 'Supply voltage' = 5 volts, R1 = 10k, R2 = 10k, R3=10k

I am getting:

V High=

**3.333333 Volt**V Low=

**1.666667 Volt**and using the same values 'Supply voltage' = 5 volts, R1 = 10k, R2 = 10k, R3=10k in link 2

I am getting:

the trigger voltage will be

and it will hold until the signal drops to

When I enter values into these input boxes on these websites I am getting different results or am I missing something!?

So if I use the boxes in link 1 for my circuit ..that is Supply voltage = 12, R1 = 10k, R2 = 4.7k, R3 (RFB) = 220k

I get..

********= the same,**~~~**= differentV High=

**3.953673 Volt ******V Low=

**3.781774 Volt ~~~**

whereas when I enter the values in link 2 I get...

V2 =

**3.953 volts**********V'2 =

**3.6098 volts****~~~**Also I do not understand what the '

**||**' means in the formulas in link 3look under

**Non-Symmetrical Schmitt Trigger**can someone enlighten me?

So basically what is the correct formula?

Last edited: