If there is ideal voltage source and load is connected to it, being the ideal voltage source it can source upto infinite current to the load and the voltage level will not drop.

Now coming to non-ideal voltage source or Voltage regulator; if the regulator is designed to source upto 100mA, it will regulate the output voltage till the load demands 100mA.
Let's say if load needs 110mA, regulator will loose its regulation and it will start droping to its earlier voltage.

My question is why does it drop? I am not looking for decoupling cap in the answer.

Thanks
-Bharat

bharat wrote on Jul 31^st, 2009, 9:42am:


The output current is supplied by a power transistor. An opamp in a feedback configuration supplies the proper gate-source voltage to this power transistor. As load increases, the opamp increases the gate-source voltage of the power transistor. The opamp gain is finite, so there is a small droop in the output voltage when a current is applied.

The regulator "loses regulation" when the opamp runs out of headroom and cannot increase the gate-source voltage of the power transistor enough to supply the desired current.  

rg