Hello, I am learning electronics. Today I tried 7805 & 7809 voltage regulators with a 12V battery.

*Though my battery is of 12V, currently it has 8.76V in it.

In my first attempt, I connected 7805 with the battery and I got ~ 8.70V in the input terminal and in the output terminal I got ~ 4.98V which is pretty obvious.

But the unexpected things happened when I connected the battery with 7809 voltage regulator.

Here in the output terminal, I got ~ 8.69V. But in the input terminal I got ~ 7.91V.

Now this is pretty unusual to me because I am using a 9V voltage regulator and if I assume that due to the internal resistance of the wire, I am loosing around ~ 0.2V then for 7809 the output reading should be ~ 8.67V!!

My question is where is the (8.67-7.91=) unsolved 0.76V? And why this isn't the case with 7805?

Thanks in advance.

 

Here in the output terminal, I got ~ 8.69V. But in the input terminal I got ~ 7.91V.

Did you measure them both at the same time? If you 12V battery is in such poor condition, the terminal voltage will drop rapidly when any load is connected.
I suggest you get a bettery battery and try again.

 

Did you measure them both at the same time? If you 12V battery is in such poor condition, the terminal voltage will drop rapidly when any load is connected.
I suggest you get a bettery battery and try again.

Ah, ok I think I got the answer. May be the problem is not with the battery.
From the datasheet, I came to know that the minimum input voltage is 11V and that's why 7809 is not regulating the voltage.