I need to design a input overvoltage protection for a 45W DC-DC converter rated for a 9-24V wall wart input (so, 45W / 9V = 5A input current at max). So far I've seen two approaches (schematics below):
- Crowbar circuit. The idea is that the TRIAC (or SCR) in case of an over-voltage will close and therefore short the input power terminals, therefore blowing the fuse and disconnecting the device.
- MOSFET switch. In case of an overvoltage the MOSFET simply opens and the high voltage simply doesn't reach the device.
I am not sure which one should I use and I haven't found anything comparing these approaches to design the overvoltage protection. So, my questions are:
- What are the general pros and cons of each of these circuits?
- What are the guidelines to which circuit one should use in a particular application?
- Which one of these should I use in my case?
- Are there any other overvoltage protection circuits I am missing?
In my particular situation, I am mostly trying to protect the circuitry that the DC-DC converter is powering, since it can be pretty expensive and the DC-DC converter itself. I have no idea about the typical transient voltages when the power is plugged in; mostly I am trying to protect the circuitry from an "idiot user" who might plug something over 24V in the power inlet (I've seen up to 36V common wall warts and I am sure there are ones with even higher voltage), since the DC-DC converter is not designed for it and might output anything it wants at this point.
This is not a medical device, nobody will die if the device fails and (AFAIK) nothing could cause a fire in case of input or output overvoltage except for, maybe, potential tantalum capacitors filtering the power in the downstream circuitry which I do not control; the end user does (the DC-DC converter is for a modular synth system).
I am interested both in an answer for my particular case and in a more broad/common one showing the guidelines for selecting the method of overvoltage protection in any case.