operation of zener diode in this circuit

[love_electronic]

Kindly tell me the operation of diode D9 (27v) in this circuit.

 

[abdulwahababid]

is there any source on left side of the circuit.???
and second 12v is DC or AC. I had never used this software

 

[love_electronic]

12v DC source is on the left side. yes its 12v DC
R19 is connected with microcontroller

 

[abdulwahababid]

I think the only need of zener in that particular point is dissipation because for switching purpose single Diode is enough.

 

[siddarth.ghaste]

This arrangement will allow for flyback voltage to go higher, therefore helping to dissipate stored energy in coil much faster and dramatically decreasing relay release time. Zener diode voltage should be lower than transistor breakdown voltage, which you can find in that transistor’s datasheet.

 

[ngochaigv888]

It is used for voltage more 27V crossing to diode D8. I think voltage smaller not fight back
sorry. my english bad.