- Joined Oct 21, 2015
The circuit shown below is taken from this whole design. I understand the main idea. They want to measure some voltage condition and trigger something else with the comparator. R39 and C38 form a low pass filter. R37 is the pull-up resistor as the comparator's output is open collector. D19 and D20 are protection diodes as the input goes positive and negative. What I don't understand is the arrangement of the resistors R36, R38, R35, and R40. Why are R36 and R38 referenced to ground in the midpoint? According to the reference design, the input AC voltage is 230 VAC 50/60 Hz. I know this is something basic, but I'm just confused.