To convert an output current flowing in a power MOS transistor constituting a power element in a power circuit of a switching control system to a voltage and detect it with high precision and high sensitivity, without generating power loss and voltage loss ad depending upon current mirror operation which is liable to deterioration in detection accuracy.
This current detecting circuit 2 is provided with a first MOS transistor Q1 interposing between a voltage detecting point 'out' and the drain of a power MOS transistor Qm, and a second MOS transistor Q2 interposing between the voltage detecting point 'out' and the source of the power MOS transistor Qm. The first MOS transistor Q1 is made to be turned on/off with the same phase as the on/off of the power MOS transistor Qm. The second MOS transistor Q2 is made to be turned on/off with a phase reverse to that of the on/off of the power MOS transistor Qm.
YOKOTA KENICHI
CHIBA MAKOTO
HITACHI TOBU SEMICONDUCTOR LTD