Reliable industrial electronics often have protection circuits to head off any overvoltages on the supply lines and protect the electronics from damage. Overvoltages can arise when fast load changes occur on the power-supply line. Parasitic line inductance may result in high voltage spikes.
This issue can be addressed with an input protection circuit like that shown in Figure 1, which integrates an LTC4380 from Analog Devices. Power switch M1 is in the conductive path. If an overvoltage occurs at VIN, switch M1 is operated in the linear region. It causes M1 to behave as a resistor in the ohmic region, allowing VOUT to be regulated by the voltage drop across MOSFET M1.