secondary synchronous rectifier switches q 5 q 6 consisting of active switches such as mosfets bipolar junction transistors bjts or other types of controllable devices rectify the transformed alternating current back to dc the diodes d 5 and d 6 connected across the synchronous rectifier switches q 5 and q 6 can be either the body diodes of switches q 5 and q 6 or external diodes the control law selector circuitry 305 is responsible for determining when the converter is in a no load light load startup or shutdown mode of operation said differently the control circuitry should distinguish between conditions that indicate a normal positive power flow current sourcing and conditions that indicate potentially substantial negative power flow current sinking thus some negative power flow or reverse current may be allowed depending on the application although at the time of switching modes it is desirable for the instantaneous current flow to be greater than or equal to zero the predetermined threshold level for allowable reverse current flow will vary depending on the particular implementation and the design requirements for example if an output bus is driven high through a low power unit any current sufficient to pull the unit into current limit would disrupt the bus a condition that should be avoided thus the current level required to disrupt the bus is the starting point for designing the threshold level for a typical system one or two amps of reverse current may be allowable the direction and magnitude of power flow at any given time can be determined using any of a number of characteristics of the circuit commonly known in the art to be directly related to the direction of power flow these characteristics include but.