Patent ID: 7557545
Filing Date: 2009-07-07
Classification: H02M,Y02B

Abstract:
1. An electronic power unit having a continuous conduction mode in which a current flowing in the load is more than zero and a discontinuous conduction mode in which a current flowing in the load takes a negative value or zero for a specific period, the unit comprising: a first MOS transistor which applies a voltage to the load; a second MOS transistor which remains on while the first MOS transistor remains off and which rectifies the current flowing in the load; a digital control circuit which turns on the first transistor upon a lapse of a first time interval from a time the second MOS transistor is turned off and which turns on the second MOS transistor upon a lapse of a second time interval from a time the first MOS transistor is turned off, the digital control circuit controlling the on-period of the first MOS transistor so that the voltage applied to the load is constant in the discontinuous conduction mode, and determining, while the voltage applied to the load is constant, an optimal value of the first time interval from a duty which is a ratio of the on-period to a sum of the on- and off-periods of the first MOS transistor in one cycle; and a sensor which detects a current flowing in the second MOS transistor or an output voltage of the second MOS transistor; wherein the digital control circuit searches for the first time interval at which the duty is minimum with reference to a time at which an arbitrary current value is detected by the sensor, obtains a time difference between the time that the arbitrary current value is detected and a start time of the first time interval, and outputs a control signal to turn off the second MOS transistor after a lapse of a time difference from the detection of the arbitrary current value by the sensor.