Hi all. I want to use a fuse model for short circuit protection in my circuit. The model works fine when a pwl source is used(please see the figure). It goes to open circuit when 100mA is reached and waits for 1u to do so. This is because I adjusted the original library for a quick response, which had this response time equal to 0.5s. When I insert the fuse into the circuit below, however, it can not limit the current flowing through it to 100mA but rather pull it down to 5kA(simulation tool shows 5MegA when both resistors are shorted without the fuse). More interestingly, when two of these are connected in series, the current becomes 2.5kA. Is this behavior related to the internal structure of the fuse where the resistance is gradually increased within some time, which, in this case not sufficient enough to reach megaohms to limit current and behave as an open circuit? The short circuit condition occurs in 1n as the voltage controlled switch is fed with a pulse with this rise time and the fuse may not be as quick as needed. The library file and schematic is attached. Any advice on other short circuit protection setups possibly with realistic models of real parts is appreciated.

 

The short circuit condition occurs in 1n as the voltage controlled switch is fed with a pulse with this rise time and the fuse may not be as quick as needed.

I know of no real situation where a source with that fast a rise-time would need a fuse.
Exactly what real-world circuit are you concerned about?

 

I know of no real situation where a source with that fast a rise-time would need a fuse.
Exactly what real-world circuit are you concerned about?

That 1n rise-time is not the rise-time associated with a real life source. It is the time that it takes for the Vout node voltage to change and current through that net to go MegA levels. Because I model this short circuit occurence with an ideal voltage controlled switch. Instead of a fuse I tried to use a third voltage controlled switch, which is controlled by a behavioral voltage source that outputs 0V when both resistors are shorted and 3V otherwise. Even in this ideal model there is a spike of current reaching Megohms that lasts about 0.5n. Though this is not a circuit to be “realized”, I wanted to use the fuse because it is closer to reality than vcs & bvs setup.

 

huh ? Define clear specs

 

huh ? Define clear specs

I just want to add protection against short circuit, no other specifications on that. I was concerned with all these time parameters because I think fuse not being able to limit the current to 100mA but only pull it down to kA’s was related to them.

 

You can use a fast-blow fuse or a PTC polyfuse which acts like a slow-blow recoverable fuse.