A transient suppressor for 12V systems can be quite useful, especially in automotive/marine environments which have a high degree of short transients and can exhibit load dumps with peak voltages in excess of 100V. This is of course a very nasty environment for electronics, so making a transient suppressor for sensitive/cheap electronics is a good idea.

The LT4356 is a really nice device that manages to pull off a whole lot of functionality, it uses an external mosfet as  a pass element that it uses as a linear regulator when the input voltage exceeds some set threshold, and it turns the output off completely if the input voltage is too high for too long. It also manages overcurrent situations and has an extra internal amplifier that is used in the following circuit as a low-battery cutoff with hysteresis.

The designed circuit is based pretty much entirely on the sample circuits in the datasheet, with the IRFR3710Z mosfet. It limits the output voltage to 16V, and cuts off after about 1-10ms (depending on the voltage and load current). It’s designed for 8A, which at 12V is about 100W, which is sufficient for most applications. This limit is mostly due to the connection interface used (“Cigarette lighter plugs”).

Eagle libraries for the extra components, schematic and board are available here.