LDO Iq問題

daniel0613

For bipolar transistors, the quiescent current increases proportionally with the output current, because the series pass element is a current-driven device. In addition, in the dropout region the quiescent current can increase due to the additional parasitic current path between the emitterand the base of the bipolar transistor, which is caused by a lower base voltage than that of the output voltage. For MOS transistors, the quiescent current has a near constant value with respect to the load current since the device is a voltage-driven device. The only things that contribute to the quiescent current for MOS transistors are the biasing currents of band–gap, sampling resistor, and error amplifier. In applications where power consumption is critical, or where small bias current is needed in comparison with the output current, an LDO voltage regulator using MOS transistors is essential.

這是我在看LDO文章一段看不太懂..
4 b6 q4 B$ q' T/ C3 [為什麼在Drop-out region時,quiescent current 會變大??
有大大可以解釋一下原理給我 知道嗎?
越詳細越好~謝謝
( U9 a$ o; l# Y$ o, c!!

sea11038

大概的意思，双极的调整管是电流控制器件，静态电流跟输出电流成正比。在Drop-out region時，集射极电压很小，三极管工作在饱和区(不是MOS管的饱和区概念)，放大倍数要下降很多，输出同样的电流就需要更大的基极驱动电流，因此静态电流(主要是耗散在三极管基极的电流)会变大。

daniel0613

請問有公式可以導出來嗎?我還是有點一知半解!!謝謝~

kj.guo

建议你这样想：对于MOS 是电压控制电流 因此gate电流几乎为零
8 |2 f- q# {; }4 N+ b但是BJT是电流控制电流，base 电流就是所说的静态电流（它对电路来说是额外的消耗）