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开关电源设计：何时选择BJT优于MOSFET？

开关电源设计：何时选择BJT优于MOSFET？

浏览：35次 | 提问时间： 07-24 09:16

MOSFET、IGBT、BJT各自适合于哪些应用？开关电源的主要用途是不是保持输出电压的稳定？

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笑靥 07-24 09:17

开关电源电气可靠性设计1供电方式的选择集中式供电系统各输出之间的偏差以及由于传输距离的不同而造成的压差降低了供电质量，而且应用单台电源供电，当电源发生故障时可能导致系统瘫痪。分布式供电系统因供电单元靠近负载，改善了动态响应特性，供电质量好，传输损耗小，效率高，节约能源，可靠性高，容易组成N＋1冗余供电系统，扩展功率也相对比较容易。所以采用分布式供电系统可以满足高可靠性设备的要求。2.2电路拓扑的选择开关电源一般采用单端正激式、单端反激式、双管正激式、双单端正激式、双正激式、推挽式、半桥、全桥等八种拓扑。单端正激式、单端反激式、双单端正激式、推挽式的开关管的承压在两倍输入电压以上，如果按60％降额使用，则使开关管不易选型。在推挽和全桥拓扑中可能出现单向偏磁饱和，使开关管损坏，而半桥电路因为具有自动抗不平衡能力，所以就不会出现这个问题。双管正激式和半桥电路开关管的承压仅为电源的最大输入电压，即使按60％降额使用，选用开关管也比较容易。在高可靠性工程上一般选用这两类电路拓扑。2.3控制策略的选择在中小功率的电源中，电流型PWM控制是大量采用的方法，它较电压控制型有如下优点：逐周期电流限制，比电压型控制更快，不会因过流而使开关管损坏，大大减小过载与短路的保护；优良的电网电压调整率；迅捷的瞬态响应；环路稳定，易补偿；纹波比电压控制型小得多。生产实践表明电流控制型的50W开关电源的输出纹波在25mV左右，远优于电压控制型。硬开关技术因开关损耗的限制，开关频率一般在350kHz以下，软开关技术是应用谐振原理，使开关器件在零电压或零电流状态下通断，实现开关损耗为零，从而可将开关频率提高到兆赫级水平，这种应用软开关技术的变换器综合了PWM变换器和谐振变换器两者的优点，接近理想的特性，如低开关损耗、恒频控制、合适的储能元件尺寸、较宽的控制范围及负载范围，但是此项技术主要应用于大功率电源，中小功率电源中仍以PWM技术为主。

鱼 07-24 09:25

首先是恰当地选用合适的元器件：①尽量选用硅半导体器件，少用或不用锗半导体器件。②多采用集成电路，减少分立器件的数目。③开关管选用MOSFET能简化驱动电路，减少损耗。④输出整流管尽量采用具有软恢复特性的二极管。⑤应选择金属封装、陶瓷封装、玻璃封装的器件。禁止选用塑料封装的器件。⑥集成电路必须是一类品或者是符合MIL－M－38510、MIL－S－19500标准B－1以上质量等级的军品。⑦设计时尽量少用继电器，确有必要时应选用接触良好的密封继电器。⑧原则上不选用电位器，必须保留的应进行固封处理。⑨吸收电容器与开关管和输出整流管的距离应当很近，因流过高频电流，故易升温，所以要求这些电容器具有高频低损耗和耐高温的特性。在潮湿和盐雾环境下，铝电解电容会发生外壳腐蚀、容量漂移、漏电流增大等情况，所以在舰船和潮湿环境，最好不要用铝电解电容。由于受空间粒子轰击时，电解质会分解，所以铝电解电容也不适用于航天电子设备的电源中。

蛊惑我的温柔 07-24 09:34

元器件可靠性问题即基本失效率的问题，这是一种随机性质的失效，与质量问题的区别是元器件的失效率取决于工作应力水平。在一定的应力水平下，元器件的失效率会大大下降。为剔除不符合使用要求的元器件，包括电参数不合格、密封性能不合格、外观不合格、稳定性差、早期失效等，应进行筛选试验，这是一种非破坏性试验。通过筛选可使元器件失效率降低1～2个数量级，当然筛选试验代价(时间与费用)很大，但综合维修、后勤保障、整架联试等还是合算的，研制周期也不会延长

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