双极晶体管怎么并联连接

如果平衡电阻与发射极串联，则双极晶体管（BJT）可以并联连接。
随着温度的升高，BJT通常会变得更具导电性。
以下MMBT2222A数据表中的示例显示了该器件的典型增益如何随温度在允许的工作范围内变化而变化3至5倍。
这导致并联工作的BJT中的热不稳定性，因为即使两个晶体管及其相关的基极电阻完全相同（这是不可能的），它们之间的任何微小温差都会导致其中一个开始传导更大部分的共用
电流，它会使它变得更热，并携带更多的共享电流，甚至变得更热，直到某些东西最终破裂。
通常，如果平衡电阻器与发射器而不是基极串联放置，则BJT可以更可靠地并联操作。
即使是这里的小电阻也会强烈抵消不平衡的趋势，因为流过任何一个晶体管的电流的增加导致所施加的基极 - 发射极电压降低。
这反过来减少了流动的基极电流量，因此减少了受影响的晶体管承载的共用电流部分。
这种技术通常被称为“发射器退化”。



以下为原文

        Bipolar Transistors (BJTs) can be connected in parallel if balancing resistors are placed in series with the emitter.
BJTs generally tend to become more conductive as their temperature increases.  The example below from MMBT2222A datasheet shows  one how this device’s typical gain can change by a factor of 3 to 5 times as its temperature varies over the allowed operating range.  This causes thermal instability in BJTs operated in parallel, because even if the two transistors and their associated base resistors are perfectly identical (which is impossible), any slight temperature difference between them will cause one of them to begin conducting a greater portion of the shared current, which will cause it to become hotter, and carry even more of the shared current, and become even hotter still, until something eventually breaks.

Typically, BJTs can be more reliably operated in parallel if balancing resistors are placed in series with the emitter, rather than the base.  Even a small resistance here will strongly counteract the tendency for imbalance, because an increase in current flowing through any one transistor causes the applied base-emitter voltage to decrease.  This in turn reduces the amount of base current that flows, and therefore the portion of the shared current that the affected transistor carries.  This technique is commonly known as “Emitter Degeneration.”