Analysis of the switch input circuit composed of four diodes

bigbat

Analysis of the switch input circuit composed of four diodes [Copy link]

This is a switch input circuit composed of four diodes that I saw on the Internet. The analysis is as follows: 1. When SW1 is open, R7-D5-R5 forms a path, the voltage at point A is about 10V, point B is about 3.3V, point C is basically around 3.3V, and the VPIN state is high. 2. When SW1 is closed, R7-D6 forms a path, the voltage at point A is about 0V, point B, R5-R6 form a path, about 0V, point C is basically around 0V, and the VPIN state is low. Discussion: What is the role of C1 here? What is the role of D6?

masterliu

C1 may be the influence of the circuit's own noise or the noise in the power supply on the circuit, so it plays a filtering role; I can't see what the use of D6 is.

bigbat

The function of D6 is to limit the voltage. When the circuit is connected to a voltage higher than 12V, diode D6 is in a biased state, the circuit is 12V input, and no one knows what voltage SW1 will be connected to.