| US 7,557,545 B2 | ||
| Electric power unit operating in continuous and discontinuous conduction modes and control method therefor | ||
| Toshiyuki Naka, Fuchu (Japan); Akio Nakagawa, Chigasaki (Japan); and Kazutoshi Nakamura, Yokohama (Japan) | ||
| Assigned to Kabushiki Kaisha Toshiba, Tokyo (Japan) | ||
| Filed on Jul. 13, 2006, as Appl. No. 11/485,466. | ||
| Claims priority of application No. 2005-206086 (JP), filed on Jul. 14, 2005; and application No. 2006-187292 (JP), filed on Jul. 07, 2006. | ||
| Prior Publication US 2007/0013351 A1, Jan. 18, 2007 | ||
| Int. Cl. G05F 1/618 (2006.01) | ||
| U.S. Cl. 323—223 [323/283; 323/285] | 12 Claims |
| 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.
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