| 摘要 |
PURPOSE:To reduce current capacities of main switches, by providing the switching circuit for switching, according to the desired output voltage of a switching power supply, the inphase ON-OFF control mode of the two main switching elements of the primary sides of the transformers of respective converters to the ON-OFF control mode wherein the switching phases of the two main switching elements are shifted by 180 degrees from each other, and vice versa. CONSTITUTION:A mode switching circuit for switching the inphase switching mode of two converters to the push-pull switching mode thereof, and vice versa. By providing this mode switching circuit additionally, when there are two sizes respectively in the output voltage and current of a switching power supply, two main switching elements Q1, Q2 are driven in either inphase mode or push-pull mode. Thereby, when the output voltage is small and the output current is large, the utilization factors of the main switching elements can be improved. Also, even when the output voltage is small and even when the output voltage is large and the output current is small, IOmax's can be made equal to each other too, i.e., the utilization factors of the main switching elements Q1, Q2 can be made equal to each other too. Therefore, by decreasing the current capacities of the main switches, the size of the switching power supply can be reduced. |
