Patent ID: 8710756

Claim:
An active constant power supply apparatus for supplying constant power to a load, the active constant power supply apparatus comprising: an AC power supplier for supplying AC power; a rectifying circuit which receives the AC power from the AC power supplier and rectifies the received AC power; a driving coil connected in series to the load receiving power from the rectifying circuit; a power switch for switching on/off a current passing through the driving coil and the load; a free-wheeling diode, both ends of which are connected to an outer terminal and an input terminal of the load, respectively, so that the free-wheeling diode is connected to the load in parallel, the free-wheeling diode being installed such that the current flows from the output terminal of the load to the input terminal of the load to discharge the current charged in the driving coil to the load when the power switch is switched off; a pulse-type driving signal generator connected to a gate terminal of the power switch to control the switching on/off operation of the power switch; a turn-off decider which generates a turn-off signal when the current flowing along the driving coil has a value higher than a designed value, so as to switch off the power switch; and a pulse width controller which measures an adjustment term ranging from a switch-on time of the driving signal generator to a switch-off time of the turn-off decider in a unit of one period of a rectifying voltage while the power is being supplied to the load to acquire and store a minimum adjustment term, and controls a driving pulse width of the driving signal generator such that the driving pulse width coincides with the adjustment term in and after a next cycle of power supply, wherein the pulse width controller includes a pulse width measurement comparator (or a pulse width adjustment decider), a start point is set as a time at which the current flowing through the driving coil is 0 A, an end point is set as a time during which the pulse width measurement comparator is operated in a level less than the designed value, and the pulse width controller measures a gradient of the current flowing through the driving coil based on the start point and the end point and sets the adjustment term according to the gradient of the current or sets the adjustment term such that the pulse width measurement comparator has a predetermined frequency of operations.