Patent ID: 6122180
Filing Date: 2000-09-19
Classification: H02M

Abstract:
In a switching mode power supply (SMPS) comprising a rectifier that rectifies alternating current (AC) power to direct current (DC) power, a transformer that induces the rectified power to a secondary coil through a primary coil to transform the power into the power required by the system, a switching element that is electrically coupled to the primary coil, and a pulse duration modulator that controls a switching operation of the switching element, a constant power control circuit, comprising:a current detector, located in the secondary coil of the transformer, detecting the current flowing to the secondary coil;a current controller including a first comparator that compares the voltage corresponding to the current detected by the current detector with a predetermined first reference voltage;a load, electrically coupled to the secondary coil of the transformer to receive the power flowing to the secondary coil;a voltage controller detecting the voltage at the load, comparing the detected voltage with a second reference voltage, and outputting a difference in voltage between the detected voltage and the second reference voltage;a constant power controller receiving the current controlled by the current controller and detecting the voltage of the secondary coil, comparing the detected voltage with the first reference voltage, and outputting a difference in voltage between the detected voltage and the first reference voltage;an amplifier receiving outputs of the voltage detector, the current detector, and the constant power detector, and amplifying the outputs to a predetermined gain value and outputting the result; anda switching controller receiving an output of the amplifier and determining the power of the secondary coil, and controlling the switching duty of the switching element depending on whether the determined power of the secondary coil is above or below the first reference voltage.