Apparatus For Bi-Directional Power Switching In Low Voltage Vehicle Power Distribution Systems

Abstract

A plurality of modules each including at least a pair of series connected power MOSFETs are configured between a plurality of DC voltage sources, and a plurality output terminals for connection to respective loads, are controlled for selectively applying power to the loads via time delay switching incorporating forward biased intrinsic diodes of the MOSFETs in a given current path during initial application of power to a load, whereby a predetermined period of time after turning on one of the series connected MOSFETs, the associated other MOSFET is turned on to shunt its intrinsic diode for reducing the resistance in the current path to maximize current flow. The configuration of the plurality of power MOSFETs is also controlled for selectively providing bi-directional current flow between said plurality of DC voltage sources.

What is claimed is: 
     
         1 . In a low voltage high current DC power distribution system, the method comprising the steps of:
 connecting an output of a primary battery to a drain electrode of a first power MOSFET switch;   connecting a source electrode of said first power MOSFET switch to a source electrode of a second power MOSFET switch;   connecting a drain electrode of said second power MOSFET switch to an output of a secondary battery;   comparing the voltage level of said primary battery to that of said secondary battery; and   operating a controller in a first mode to sense when the voltage level of the primary battery is greater than that of the secondary battery, for applying a control signal to a gate electrode of said first power MOSFET switch for turning it on to connect said primary battery through the relatively high resistance of a body diode of said second power MOSFET switch to said secondary battery, and after a predetermined period of time applying a control signal to a gate electrode of said second power MOSFET switch to turn it on to shunt its body diode with its relatively low resistance channel, for substantially reducing the resistance in the current path between said primary and secondary batteries.   
     
     
         2 . The method of  claim 1 , further including the step of:
 operating said controller in a second mode to sense when the voltage level of the secondary battery is greater than that of said secondary battery, for applying a control signal to a gate electrode of said second power MOSFET switch for turning it on to connect said secondary battery through the relatively high resistance of a body diode of said first power MOSFET switch to said primary battery, and after a predetermined period of time applying a control signal to a gate electrode of said first power MOSFET switch to turn it on to shunt its body diode with its relatively low resistance channel, for substantially reducing the resistance in the current path between said primary and secondary batteries.   
     
     
         3 . The method of  claim 2 , further including the step of:
 operating said controller in a third mode to sense when the voltage levels of the primary and secondary batteries are equal, for simultaneously applying control signals to the gate electrodes of said first and second power MOSFET switches for turning them on to establish a relatively low resistance current path between said primary and secondary batteries.