Inverting Schmitt Trigger using 741

Dear all,

I am now desperate of solving this last problem in my assignment, it now took me 2hours to figure this out but no luck. I am still confused after searching the net and all i found is non-inverting. If you guys can help me i will really appreciate it.

The problem is to design an "inverting" Schmitt Trigger circuit using 741 OP amp with the supply of 9V to have UTP = 0v and LTP = -3v.

The UTP = 0v makes me confused. It is breaking my head. Will someone explain to me how to get the Resistors with the UTP = 0v? I know this is a newbie question but please help me..

The lousy old 741 opamp was designed for and is spec'd for only a 30V supply. So many of them do not work from a 9V battery that drops to 6.0V during its life.
Its inputs do not work if they go below +3V or are higher than +6V in your circuit that is powered from +9.0V and 0V.

The 741 opamp will work in your circuit if it has +9V and -9V supplies.

iamboo said:

Dear all,

I am now desperate of solving this last problem in my assignment, it now took me 2hours to figure this out but no luck. I am still confused after searching the net and all i found is non-inverting. If you guys can help me i will really appreciate it.

The problem is to design an "inverting" Schmitt Trigger circuit using 741 OP amp with the supply of 9V to have UTP = 0v and LTP = -3v.

The UTP = 0v makes me confused. It is breaking my head. Will someone explain to me how to get the Resistors with the UTP = 0v? I know this is a newbie question but please help me..

Click to expand...

Hello,


If you have a stable 9v to work with and you use a different op amp like the LM358 you can use the first circuit shown in the attached diagram. If you are using the 741 though you may have to bias the input up a little so that it comes within the common mode range of the 741 and that is the second circuit shown below.
Both circuits are shown with the input set point around 3v but you can adjust as needed. The second circuit assumes the input source impedance is much less than 10k, but you can raise that by raising the impedance of the associated network of 10k and 30k.
The teacher may not care as much about the input common mode range of the 741 so you'll have to ask.