I was developing a footwell controller for my car, using RGB LEDs for the lights, an Arduino Nano for RGB controlling and an auxiliary PWM generator
(pure white lights) when the Arduino is off. The two signal sources are complementary.
The problem arises at the end stage when the two signals have to merge to drive the MOSFETs (PWMR, PWMG and PWMB comes from the Arduino):
The square wave coming from AUXPWM after it passes the 1N4148 is completely destroyed, it isn't able to drive the MOSFET anymore. The LTSpice simulation produces this graph from the schematic above:
It's possible to see how the signal is almost flat after passing through the diode. I really cannot understand what is happening here, so am I missing some underlying knowledge or is the simulation plain wrong?
Edit: the MOSFET are N-Channel I did the schematic wrong, sorry