The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> Question on ideal and non-ideal Voltage Source
https://designers-guide.org/forum/YaBB.pl?num=1249058554

Message started by bharat on Jul 31^st, 2009, 9:42am

Title: Question on ideal and non-ideal Voltage Source
Post by bharat on Jul 31^st, 2009, 9:42am

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

Title: Re: Question on ideal and non-ideal Voltage Source
Post by raja.cedt on Jul 31^st, 2009, 10:50am

hi,
i donno what you are expecting, if you can design regulator with infinite loop gain then you argument is correct, but general voltage regulator's has finite loop gain hence non zero infinite, so max load current spec is there....... does it answer your question?

Thanks,
Rajasekhar.

Title: Re: Question on ideal and non-ideal Voltage Source
Post by RobG on Jul 31^st, 2009, 10:44pm

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

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.

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