Hi. I am trying to make a circuit that will accept a voltage from 0 to 30v and limit it to 3.3v as a TTL input to my microcontroller. I am using a "classical" (i.e. often used, so I understand) design of two Schottky diodes in series (attached). In LT Spice simulation the voltage is approx 3.4v at the junction of R1/D1/D2. But in real life when I build the circuit, I get voltages all across the board all the way up to a limit of 5.7v for an input above 20v (where it seems to finally stop). Why is it not just staying at 3.4v like in the simulation? Thanks.