I am designing a circuit to protect a load from over-voltage. The voltage at the load must be around 380VDC and the current consumption will be around 2A. In normal operation the Power Supply must increase the voltage as the load pulls more current so that the voltage drop across the cable is compensated. However, if by any reason the power supply shoots the voltage to 800VDC, the circuit on the load must be opened, avoiding the load to see such a high voltage. The power supply is capable of delivering 8A.

I tried the circuit in the picture, it works pretty well as it opens at 400VDC (triggered by the two zeners in series). But at 500VDC the zeners blow up even with a 150k resistor.

Would a crowbar work in this situation ? I really don't want to use glass fuses to avoid opening the enclosure where the load is installed.

Any ideas?

enter image description here

  • \$\begingroup\$ A crowbar would blow probably blow a fuse somewhere... So I guess you'd have to open a box anyway. \$\endgroup\$ Nov 6, 2018 at 4:54

1 Answer 1


Please Look at the following picture

https://eenews.cdnartwhere.eu/sites/default/files/images/01-edit-photo-uploads/2012/2012-03-march/linear-technology/fig-3a.jpg inside the link http://www.eenewsautomotive.com/content/high-voltage-surge-stoppers-ensure-reliable-operation-during-power-surges/page/0/1

A circuit based on LTC4366 with proper changes could do the job for you. Moreover the circuit could make the output open by proper triggering the SD input.

  • \$\begingroup\$ Sorry for the delay, just had time now to go over it. I tried the LTC4366 and it works very well however there is still something I overlooked and is causing the mosfet to be damaged. \$\endgroup\$
    – JG_Bozza
    Nov 29, 2018 at 19:09
  • \$\begingroup\$ The circuit is very close to your limitations. the chip manufacturer must have proper recommendation for you but If you know the cause of the damage, there is always a way to add some components to prevent it. \$\endgroup\$
    – BD_CE
    Dec 2, 2018 at 4:11

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.