Failsafe circuit with transistor and Photodarlington

[gauchosuizo]

Hi everybody

I want to make the circuit below failsafe. Doe's anybody have any idea? The circuit must be as simple as possible.

Thank you in advance.

Pablo

 

[ghydda]

Failsafe in what respect?
Input surges?
Disconnections due to a bad soldering job?
Shorts?
Reverse supply voltages?

Please elaborate.

 

[eem2am]

it already looks failsafe to me...at least i cant see it exploding anyhow ...as long as you dont put too much input voltage in

 

[gauchosuizo]

Hi

thank you for your answers. The circuit must have a defined state if something would happen. It means, if some part (Transistor, Photodarlington, etc) would break down, the status always must be the same (e.g. high).

Thank you in advance

Pablo