I have seen this circuit a few times. It takes a common 3 pin LDO, and adds a PNP transistor between VIN and VOUT, to increase the amount of current it can provide at the regulated voltage. It is present in the On Semi LM7805 datasheet.
At this time I'm looking at the Holtek 7133, a 30mA 3.3V fixed LDO. It also has the same circuit.
With VIN at 5V and Tr1 a common 2n3906 100mA PNP transistor, how would I calculate R1? How much does this change the quiescent current of 5 microamps? What's the minimum VIN required for this to work with this PNP (The LDO only needs a 0.2V drop out at max).
And what is the new maximum current in this configuration? Since R1 limits VIN, I'm assuming that all the load current goes through the PNP, so in this case 100mA, not the LDO's + the PNP's 30mA + 100mA.
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