#### Mikebits

##### Well-Known Member

I assume the 3904 is a current source for the heater, but I am puzzled to what is the feedback path for Op amp A1? The .1uF cap blocks DC feedback and since this is a DC circuit I am at a lost how A1 and its feedback path work. What I am saying is, I do not understand this circuit and its operation. Where the heck is the feedback path for A1?

Thanks