| 摘要 |
PURPOSE: A switching mode power supply is provided to reduce power consumption due to a transformer during waiting power and reduce noise during initial operation and over current protection. CONSTITUTION: A switching mode power supply comprises an RFI filter(10), a rectifying and smoothing unit(20), a pulse transformer(30), a rectifying and smoothing unit(40), an output(50), a feedback(60), a breaker(70), an output control circuit(80) and a switching unit(90). The output control circuit(80) includes a pulse controller(81), an over current protecting unit(82), an output controller(83), a voltage controller(84), a frequency skipping unit(85) and a soft starting unit(86). The pulse controller(81) outputs a pulse to the switching unit(90). The over current protecting unit(82) detects variation of the pulse due to output load of the pulse transformer(30). The output controller(83) sets on/off duty cycle of the pulse transformer(30). The voltage controller(84) adjusts the width of the pulse. The frequency skipping unit(85) lowers a switching frequency in a waiting mode. The soft starting unit(85) avoids maximum current at the first side of the pulse transformer(30).
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