三端可调集成稳压器通过三极管扩流

shangdawei · 发表于 2014-12-2 09:39:26

The MC7800 series can be current boosted with a PNP transistor. The MJ2955 provides current to 5.0 A.
Resistor R in conjunction with the VBE of the PNP determines when the pass transistor begins conducting;
this circuit is not short circuit proof. Input/output differential voltage minimum is increased by VBE of the pass transistor.

[size=14.3999996185303px] 带过流保护的扩流电路

The circuit of Figure can be modified to provide supply protection against short circuits

by adding a short circuit sense resistor, RSC, and an additional PNP transistor.

The current sensing PNP must be able to handle the short circuit current of the three–terminal regulator.

Therefore, a four–ampere plastic power transistor is specified.

[size=14.3999996185303px]扩大78L××输出电流的电路，并具有过流保护功能。

[size=14.3999996185303px]电路中加入了功率三极管T1，向输出端提供额外的电流IO1，使输出电流IO增加为IO= IO1+ IO2。其工作原理为：

[size=14.3999996185303px]在电路中存在关系式VBE1 =VR1 =VCE3。

[size=14.3999996185303px]正常工作时，T2、T3截止，电阻R1上的电流产生压降使T1导通，使输出电流增加。

[size=14.3999996185303px]若IO过流（即超过某个限额），则IO1也增加，电流检测电阻R3上压降增大使T3导通，导致T2趋于饱和，

[size=14.3999996185303px]使T1管基-射间电压VBE1降低，限制了功率管T1的电流IC1，保护功率管不致因过流而损坏。