Hint for @Ash

You can use CMOS Schmitt triggers when you don't need precision thresholds. That saves on component count/complexity significantly.

Typical chips: 74HC14 (in 5V logic), 4093, 40106, 4584

CD4093 is 2-input NAND, so it can perform some useful logic functions at the same time.

Medved :

The PNP transistor is pretty much what is done in my 2nd circuit (P-MOSFET here, same idea)



Driving everything with the comparator outputs directly would mean connecting everything to the same point. With open collector comparators this is definitely a problem, as the intermediate voltage on the dividers etc will appear on the gates of the MOSFETs that shut down signals. To make this work at all, voltages of the dividers would have to be carefully considered vs. the MOSFETs Vgs th.... More design constraints and worse reliability

With push/pull comparators this could work, but i dont see a justification

Small signal MOSFETs are cheap, use them to break up everything to separate lines and invert as necessary, each with its own simple design requirement, resulting in fewer constraints and compromises in the design



The protection logic paths have to remain independent, because their outputs control different things in the circuit :

 - Undervoltage and overvoltage shut down all operation modes. They short the gate drive to the MOSFETs (or if a gate driver IC is used, its inputs or enable input)

 - EOL lamp only prevent the 50% opreation - Full power with the remaining lamp is still allowed. So it shut down the switching generator IC only



RRK :
Here i do want some moderate precision for the UV and OV protections. Since i already have Vref and comparators for that, i can as well use the additional comparators in the chip for the other functions



You all may be interested to see the following part of some other project i am currently working on