where the current is not too large mosfet 50 operates in its linear region acting like a series resistor having a resistance r ds the voltage drop across mosfet 50 is simply equ2 during a load dump mosfet 50 current saturates becoming a constant current source the current through load 51 does not increase in proportion to the load dump voltage the increase in the saturation current as compared with the normal current is described as follows equ3 this means in effect that with the depletion mode device the percentage increase in current during a load dump can be minimized by running the depletion mode device during normal operation at a higher current density thus in the circuits shown in fig5 a 5d there is a tradeoff between the power loss in mosfet 50 during normal operation and the increase in current through mosfet 50 during a load dump condition fig6 a illustrates the behavior of current as a function of voltage for the resistive approach fig3 a the bipolar transistor approach fig4 a and the depletion mosfet approach shown in fig5 a 5d in all three cases the current does not increase until after the battery voltage exceeds the breakdown voltage of diode d2 i e 20 v assuming that mosfet 50 and resistor 30 are selected to offer the same linear resistance the current then rises linearly until mosfet 50 saturates and limits the current the current through resistor 30 continues to increase linearly the pnp transistor 40 behaves somewhat like mosfet 30 except that the presence of a base current increases the total current through the device fig6 b illustrates power loss as a function of voltage for the same devices the power losses in all three devices increase linearly until the breakdown.