Fairfield Korea Semiconductor Ltd.

Sang-Heum Yeon

Maeng-Ho Seo

Disclosed is an SMPS with a constant power control circuit. The constant power control circuit comprises a current detector located in a secondary coil of a transformer and which detects a current flowing to the secondary coil; a current controller including a first comparator that compares a voltage corresponding to the current detected by the current detector with a predetermined first reference voltage; a load, which is electrically coupled to the secondary coil of the transformer, for receiving the power flowing to the secondary coil; a voltage controller detecting a voltage at the load, comparing the detected voltage with a second reference voltage, and outputting a difference between the voltages; a constant power controller receiving the current detected by the current detector, detecting the voltage of the secondary coil, comparing the detected voltage with the first reference voltage, and outputting a difference between the voltages; 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; and a 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.

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Bucheon, South Korea

Sang-Heum Yeon