How to get 6.7v out from 7.2v in?

[Hooter]

I have a 7.2v 6800mah Li-ion battery. I would like to get a regulated 6.7v (or very close) out and draw about 870ma. Could I use a LM2940T 5volt fixed output with a resistor (size ?) on the ground pin to maximise output as the dropout of 0.5v is all I need? If so, what size capacitor on output? Is there a better way to achieve this?

 

[ericgibbs]

I have a 7.2v 6800mah Li-ion battery. I would like to get a regulated 6.7v (or very close) out and draw about 870ma. Could I use a LM2940T 5volt fixed output with a resistor (size ?) on the ground pin to maximise output as the dropout of 0.5v is all I need? If so, what size capacitor on output? Is there a better way to achieve this?

hi,
A Schottky diode can be used with a 0.5Vdrop at 870mA for 7.2V to 6.7V

 

[audioguru]

A "7.2V" lithium-ion battery is 8.4V when fully charged and drops to about 6V during a discharge. Then a simple regulator or a diode will not regulate the voltage at 6.7V.

 

[Diver300]

There really isn't much capacity left in a lithium - ion cell at 3.4 V. A low drop regulator will take a pair of cells down to 6.8 V while still giving out 6.7 V, and by that time the voltage is about to collapse.

You could design a regulator that would give 6.7 V out with 6 V in, but I think that it wouldn't gain as much as it would cost in loss of efficiency.