Patent ID: 9602012
Date: 2017-03-21
CPC Classifications: H02M

Claim:
1. An apparatus for controlling a switching power supply that causes a transformer to convert an input voltage on a primary side into a direct-current output voltage on a secondary side based on switching of a switching element and to supply the output voltage to load, the apparatus comprising: an output voltage error detection unit configured to output an auxiliary winding voltage generated across an auxiliary winding having the same number of turns as a secondary winding of the transformer a certain period after a secondary conduction period of the transformer starts; a correction amount calculation unit configured to calculate a secondary voltage drop caused by a secondary current flowing in the secondary conduction period based on a primary current flowing through the switching element arranged on the primary side when the secondary conduction period starts and output a result of the calculation as a correction amount to be added to a target value for the output voltage; a reference voltage generation unit configured to generate a reference voltage by adding a voltage corresponding to the correction amount to a target voltage for the output voltage; a control unit configured to perform feedback control to minimize an error between the auxiliary winding voltage obtained after a certain delay period and the reference voltage and generate a feedback signal; and a pulse width modulation (PWM) generation unit configured to control a PWM signal based on the feedback signal, adjust switching of the switching element, and perform a control operation to maintain the output voltage at a constant level.