| 摘要 |
PROBLEM TO BE SOLVED: To provide a half bridge type switching power supply capable of easily preventing a transformer from being eccentrically excited and saturated by influences of a difference between conduction times of two switching elements.SOLUTION: The switching power supply includes: an output voltage monitor part 26 which outputs a control signal Vs to be increased/decreased by amplifying a difference between an output voltage Vo and a target value Vr; a pulse width modulation part 28 which performs modulation upon receiving the control signal Vs, determines on-time ratios Don1 and Don2 and outputs drive pulse-time ratio signals Vd(Don1) and Vd(Don2); and a drive pulse generation part 30 which generates first and second drive pulses Vg1 and Vg2 corresponding to the drive pulse-time ratio signals Vd(Don1) and Vd(Don2). A minimum-time ratio Dmin that is a value greater than zero is set to the pulse width modulation part 28. When the control signal Vs is changed in a direction to reduce the output voltage Vo, the on-time ratios Don1 and Don2 are reduced gradually and, after achieving the minimum-time ratio Dmin, switched to zero.SELECTED DRAWING: Figure 1 |
