How do i make this circuit work?

Thread Starter


Joined May 17, 2008
I am aware the components are over their voltage limits. The top comparator (tp1) has a 15V output while the bottom comparator (tp2) has a 5V output. What causes this?

The green trace is a square wave and the blue trace is the inverted square wave. Everything is good except i can't figure why one is of higher voltage then the other(and how to fix it).

Sorry if this is a noob question, but i can't figure it out for the life of me.



Joined Jul 17, 2007
You don't have current limiting resistors on the bases of either of the transistors.

The top LT1720 has to supply the top transistor with 70mA of current through it's base, since there is no limiter.

The bottom LT1720 doesn't have to supply ANY current through the other transistor's base, since it's never really conducting any current.

I don't know why you're supplying 15v to a comparator that has an absolute maximum rating of 7v. That doesn't make sense.

BTW, your green trace is from TP1, and the blue trace is from TP2.

Try the attached modification.


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