| 摘要 |
There is described a control circuit for use with a switching-mode power supply which circuit operates to store the duration of the last drive pulse and to control the next drive pulse so that it is prevented from exceeding the stored value by a given increment. In this manner the increment is selected such that one maintains close drive symmetry for the output drive transistors in all modes of operation. According to the operation, a given number of cycles are required before a minimum drive pulse to an output transistor can become a maximum. Thus, one never exceeds the duty cycle or the drive symmetry between the drive signals in a push-pull switch mode power supply by more than a predetermined increment. This assures complete drive symmetry and hence results in increased power supply efficiency while preventing the undesirable saturation of the output transformer.
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