| 摘要 |
PROBLEM TO BE SOLVED: To simplify a control circuit by suppressing a phase delay, and to improve response characteristics as a power supply, while restraining an amount of change in duty to input voltage width and improving efficiency by extending a duty at high-voltage input to reduce an effective current.SOLUTION: In a switching power supply, a step-up converter section A is connected to a forward converter section B in series. In the step-up converter section A, a fundamental formula, Vout=1/(1-D)×Vin, is established when an input voltage, an output voltage, and the duty, namely a ratio of on time to switching time, are set to Vin, Vout, and D, respectively. In the forward converter section B, a fundamental formula, Vout=n×D×(1-D)×Vin, is established when a ratio of the secondary winding number of a transformer to the primary winding number is set to n. The switching of the step-up converter section A is controlled so that one of them is invariably turned on except an off period (dead time period). Further, a rectifying device is added to the step-up converter section to restrain a backflow of current, thus allowing the step-up converter section A to operate only in a discontinuous mode. |
