Recently, due to a fire caused by old photovoltaic MJB(Module Junction Box), a situation that paralyzes the photovoltaic system has frequently occurred. Most of the heat sources which cause a fire in the inside of MJB are several to dozens of the diodes preventing the reverse flow of current connected in series to each string. A heating loss occurs due to the forward voltage of the diodes. If the heating loss occurring in the diodes can be reduced, the size of MJB can be reduced. The closed MJB which is able to block sufficiently oxygen supply to an MJB will be very helpful for fire protection. Therefore, this study proposes high-efficiency photovoltaic reverse-current protection device using the synchronous switching rectification method which can greatly reduce the heat generated from the general diodes preventing the reverse flow of current in a photovoltaic MJB.