Patent ID: 8259421
Filing Date: 2012-09-04
Classification: H02M,Y02B

Abstract:
1. An apparatus comprising: an abnormal current preventive circuit in a synchronous rectification buck type DC-DC converter for providing a first Nch MOSFET at a low side, connecting a second Nch MOSFET similar to the first Nch MOSFET in parallel to the first Nch MOSFET to detect an abnormal current of the first Nch MOSFET, connecting a detection resistor between a source of the second Nch MOSFET and a ground, inputting a voltage across the detection resistor to a current comparator, and determining by the current comparator an abnormal current by converting the input voltage into a current, and comparing the current with a reference current, thereby determining the abnormal current, wherein the current comparator comprises a first current mirror configured by a first diode connected Nch MOSFET and to which a source is connected to an input terminal and a second Nch MOSFET whose gate is connected to a gate of the first Nch MOSFET; a second current minor configured by a first diode-connected Pch MOSFET and a second Pch MOSFET whose gate is connected to the gate of the first Pch MOSFET; and a current source composed of a floating constant current source for supplying an equal reference current to a drain of the first Nch MOSFET of the first current minor and a drain of the first Pch MOSFET of the second current mirror; a drain of the second Nch MOSFET of the first current mirror is connected to a drain of the second Pch MOSFET of the second current minor, at least one or more inverter is connected to a connection point, output of the inverter is connected to an output terminal of the current comparator, and output of the current comparator is determined by a comparison result between an output current of the second current mirror and an output current of the first current mirror depending on a voltage of the input terminal.