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Power adapter product type
2025-05-13
Self-excited Series Power Adapter
VT is the power adapter switch transistor, controlled by the excitation pulse, operating in cutoff and saturation states. C1 is the filter capacitor in the AC voltage rectification and filtering circuit. VD is the freewheeling diode, which provides a power supply path to the load when the switch transistor is off. L is the energy storage inductor (i.e., the switching transformer). C2 is the filter capacitor at the output of the power adapter.
Operating Process
During the saturation conduction period of the switch transistor VT, the DC voltage Ui at the positive terminal of C1 charges through L → VT → positive terminal of C2 → negative terminal of C2. On one hand, this establishes a DC voltage across C2; on the other hand, the magnetic energy in the energy storage inductor L continuously increases. When the switch transistor VT is off, L induces a voltage with negative polarity on the left and positive on the right, releasing the magnetic energy through the freewheeling diode VD to C2 and the load. The output voltage Uo of the power adapter is determined by the duration of VT's saturation conduction time, which is controlled by the base excitation pulse width. The width of the base excitation pulse is determined by the error sampling and amplification circuit.
In a series power adapter, if there is no freewheeling diode VD, when the switch transistor suddenly changes from saturation conduction to cutoff, the magnetic energy stored in L cannot be released, inducing a very high voltage. This voltage can easily cause the switch transistor VT to break down. When the freewheeling diode VD is connected, during the transition from saturation conduction to cutoff of the switch transistor, the magnetic energy in L is released through VD to C2 and the load circuit. This on one hand reduces the voltage across L, making the collector-emitter voltage drop of the switch transistor equal to the input Ui value with sufficient margin; on the other hand, during VT cutoff, L releases energy through the freewheeling diode VD, supplementing energy to the load circuit during the switch transistor's off period. This results in a smoother output voltage and higher efficiency of the power adapter.
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Phone:19924904787(Clara Xie)
Email:jingyuan1@delipower.ltd
Company Address: Building B, Fengshengyuan Industrial Park, Liaokeng Community, Shiyan Street, Bao'an District, Shenzhen
Factory Address: Buildings 5-8, Changqing Avenue Industrial Park, Lashan Street, Luoping County, Qujing City, Yunnan Province
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