Hello, I have a relay based circuit as shown below and the full schematics is in the attached document.
The circuits based on PC375 relay, how does it work?
Why they need all of those diodes and resistors?
There is no spice model so i am having trouble to know if this acctually will work.
https://pickercomponents.com/pdf/Relays/PC375.pdf

 

What is it supposed to be guarding the power supply against?? Understanding the function helps with analysis quite a bit.

 

The circuits based on PC375 relay, how does it work?

It appears when turned ON it switches the 24 volt supply and 15 volt supply through the relay contacts.
The CON_ON switch provides bias to Q6 to activate relay LS1 and maintains that bias through the 24 volt contact when the CON_ON switch is released.
Are you wanting to use that circuit for some other purpose?

 

Certainly the circuit is drawn to make analysis more difficult than it needs to be. The Zener diode, D5, is to protect the gate of the mosfet from excess voltage. The three diodes, D17, D19, D20 compose a wired-OR function allowing any one signal to pull down the logic level on the other side, which connects to an unknown entity.

 

Certainly the circuit is drawn to make analysis more difficult than it needs to be. The Zener diode, D5, is to protect the gate of the mosfet from excess voltage. The three diodes, D17, D19, D20 compose a wired-OR function allowing any one signal to pull down the logic level on the other side, which connects to an unknown entity.

That unknown entity (LS2) is a relay with 12 volts going through a NC contact providing 12 volts to relay coil LS1.
Energizing LS2 through anyone of those "OR" circuits disconnects LS1.
J29 is a mystery as I see no reference to T_RF. Must complete the connection to the coil of LS2 somehow.