寄生电容影响升压变压器的设计

　　升压设计中最关键的部件之一像图1是变压器。变压器的寄生组件，可以使他们偏离它们的理想特性和寄生电容与二次关联可引起大共鸣开关电流前沿的电流尖峰波形。这些尖峰可以导致调节器显示表现为义务的不稳定的操作条件周期不稳定。这种影响是非常高的加剧电压设计。重视变压器设计将治愈这个问题。

　　图2显示了高频电流路径的寄生电容。在操作假设分析中输入和输出电压在交流地。因此，该寄生电容并联。变压器的次级提供这些电容器的交流电流路径。流经次级产品的电流N倍于初级电流。由于寄生电容匝数比增大，初级电流逐渐变大。

　　The operation waveforms for this circuit are shown in Figure 3. When the switch （VSW pin—Trace A） is turned “on” the primary is pulled to ground. The secondary cannot instantly follow this action because of the loading effects of its parasitic capacitors. The effects of the parasitic capacitance can easily be seen in the leading edge of the switch current waveform （Trace B）。 This current spike is caused by the loading effect of the secondary parasitic capacitances. The secondary output （Trace D） swing can exceed 600V. As such， a large amount of charge （Q = C • V） is needed to swing this node during the switching transients.