I need to use 5VDC in my circuit, so I am planning to design a simple voltage regulator using LM7805 like below:
**broken link removed**
I understand that Vi must be about 3V above the desired output voltage level and below the maximum allowed input voltage level, must be chosen between these two voltage values. What I'm confused is what Vi to supply in order to use LM7805 in the most efficient way.
When we apply an input voltage Vi, does the voltage difference Vx = Vi - Vo appear on LM7805 continuously? If so, it will consume Px = Vx . Ix amount of power and it will be wasted as heat. So we should better supply a Vi voltage which is as low as possible (near 8V for my circuit).
Or, does LM7805 monitor the output voltage level, and pump electrical charge to Co capacitor whenever the voltage level at the output drops down to below a certain level? In this case, applying a high input voltage Vi will not be a much problem as was in the previous case.
How does LM7805 work? Can you please explain me the working principle of LM7805, and specify a Vi value which will make LM7805 work in the most efficient way?