So in most lithium charging circuits an LM317 is used to provide constant current.... Which makes sense...
The LM317 will output a voltage at the output pin that is proportional to the input voltage...... I was wondering if I charge a normal cell to around 3.7V... what difference would it bring whether the input voltage to the LM317 was 12V or 8V for example.... the current output is the same....
If you disconnect the battery the output of your lm317 with a 12V input is around 11.5V, however when it's 8V your output is around 7.5V....
Does that make a difference at all? when connecting the battery later if not where does the excess voltage go?

Thank you

 

The difference in input voltage should not make a noticeable difference.

Most lithium charging circuits are commercially made and use a dedicated charge controller that charges the battery with a profile that safely charges the cell to capacity.

 

So in most lithium charging circuits an LM317 is used to provide constant current.... Which makes sense...
The LM317 will output a voltage at the output pin that is proportional to the input voltage...... I was wondering if I charge a normal cell to around 3.7V... what difference would it bring whether the input voltage to the LM317 was 12V or 8V for example.... the current output is the same....
If you disconnect the battery the output of your lm317 with a 12V input is around 11.5V, however when it's 8V your output is around 7.5V....
Does that make a difference at all? when connecting the battery later if not where does the excess voltage go?

The output voltage is not proportional to input voltage.
The output voltage is whatever is required to maintain the constant-current through the battery.
If you disconnect the battery, then the output voltage will rise since its trying to maintain the constant current.

When the battery is connected, the excess voltage between the input and the battery is dropped across the LM317.
That's how it regulates the current.

But you only want a constant current up to a certain battery voltage.
Above that you need a constant voltage output.
Otherwise you can have one of those interesting lithium battery fire and explosions that you can see on Youtube .