LM 317 is a good IC Voltage regulator for small power supplies.

FIG. 1
shows another application of LM317 as ** "Constat Current source"** for

"NiCd" battery charging

How is it the "R" value?

that means 700 x 10% = 70 mA or 0.07 A... =>

R = 1.25 / 0.07 => R = 17.85 OHM

The commercial resistors have standard values 10, 12, 15, 18, 22, 27, 33 ....

so, the closer value for 17.85 is a 18 Ohm resistor .

1) input voltage must be 5-6 Volts higher... i.e. for a 7.2 V battery

case the input voltage must be 12.2 V or higher.

2) For currents above 50 mA, LM317 needs a Hotsink but keep in mind:

the central conductor has an internal - connection with metal- body of IC .

DON'T put the IC-body direct to a GND-metal box for hotsink without isolation!

In this case we have short-circuit between pin2 of LM317 and ground (--)

Finally, during charging "NiCd" batteries have a thermal-loss of about 40-50 %.

That means a higher total charging period... i.e. for a

not enough a 10 hours period (10 x 70 mA =700 mAh) but a 14-15 hours period

(total battery capacity "plus" thermal loss).

The following table has various Battery capacities and "R" values

Battery capacity |
"R" value |
Time period |