overvoltage protection

[rcpilot]

Hi
I have a voltage sensitive control panel that requires no more than 3 volts dc, I was looking at one of these http://www.ebay.co.uk/itm/221555525923 the seller says it can be set to output 3 volts, the converter would be powered from a 12 volt battery, if I put a 0.1amp fuse in the output line to the control panel it will protect it from a rise in amperage but I also want to protect the control panel from overvoltage should anything go wrong with the converter, I have seen circuits that can do this but they omit values for the components, also what ever I use it must be fast so as not to damage the control panel and it's subsiduaries, we are talking alot of money here.
Help most appreciated

[Richard]

Do an internet search for "scr crowbar schematic"

[piratepaul]

Opamps.