I was measuring voltage on zener diode and found unclear behavior of oscilloscope.
So I have function generator which puts saw wave(or sine, doesn't matter) of 20 Vpp. It goes through 1k resistor to 5.1 zener diode. Like on the picture.
If I probe the diode with DC coupling set on oscilloscope channel - I get expected waveform i.e. voltage cuts on around -0.8 Volt when forward biased and around 5.1 when reverse biased.
But when I use AC coupling on the channel, the waveform looks weird and doesn't maen anything useful at all - now it swings from -2.4 to 3.8 - which is not what you expect from this circuit.
So I get that the waveform we got is not the AC, but rather DC biased AC(though we still have -0.8 volts). But what happens with AC coupled measurement on oscilloscope? Why does it take such a weird shape? Where -2.4V and 3.8V came from?
P.S. Should stop asking silly questions in the middle of the night... AC coupling just dropped the "DC bias" to zero... duh...